Browsing by Subject "Dosimetry"
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Item Open Access A Dose Monitoring Program for Computed Radiography(2012) Johnson, JoshuaRecently, there has been a lot of effort placed on monitoring patient dose from medical procedures. The majority of people's concern has been focused on computed tomography because of the higher amounts of patient dose associated with CT exams. Our institution currently has dose monitoring programs for CT, nuclear medicine, and digital projection radiography. However, there is currently no established way to track patient dose for computed radiography. The current method of tracking computed radiography is to track exposure indicators which are not directly meaningful to patient dose. In order to address this issue, I have expanded on the exposure indicator tracking by adding a conversion for estimated patient effective dose in computed radiography.
Item Open Access An Evaluation and Comparison of Beam Characteristics, Stray Radiation Room Surveys, Organ Dose, and Image Quality of Multiple Intra-Operative Imaging Devices for Orthopedic Lumbar Spinal Surgery(2015) Womack, Kenneth RolandPurpose:
The overall purpose of this study was a comparison of radiation exposure for patients and staff during intra-operative imaging for orthopedic lumbar spine surgery. In order to achieve this, we: (1) Characterized each x-ray machine for physics performance, (2) Measured occupational radiation exposure inside the surgical suite for multiple intra-operative imaging devices utilizing currently in place clinical protocols for abdominal/spinal imaging, and (3) Measured specific organ doses for a phantom of three different Body Mass Indices (BMI) for each machine. We also compared the dose changes relative to changes in BMI as well as surgical image quality changes relative to BMI. This served as the majority of the first phase of a two phase project. The purpose of the second phase of the project will be to optimize scan parameters for surgical hardware placement in terms of image quality and organ dose for the devices that allow for modifications of scanner settings.
Materials and Methods:
(1) X-Ray quality control meters were used to verify particular beam characteristics and additional information was calculated from the beam data. Both a small volume ionization chamber as well as Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) dosimeters were used to validate linear response of new design X-Ray tubes. (2) Both handheld ionization chamber survey meters as well as Geiger-Muller based personal dose meters were used to measure stray radiation for room surveys in locations representative of typical radiation worker positions during intra-operative imaging. (3) MOSFET dosimeters were placed in an adult male anthropomorphic phantom representing a normal BMI. 20 MOSFETs were used in nine organs with two small volume ion chambers used for skin surface dosimetry. Two additional layers of adipose equivalent material were progressively added to the phantom to represent BMI values of overweight and obese.
Results:
(1) The maximum tube potential, half value layer (HVL), effective energy, and soft tissue f-factor for each machine is as follows: IMRIS VISIUS iCT: 118.4 kVp, 7.66 mm Al, 53.64 keV, and 0.934 cGy/R; Mobis Airo: 122.3 kVp, 7.21 mm Al, 51.31 keV, and 0.925 cGy/R; Siemens ARCADIS Orbic 3D: 83 kVp, 7.12 mm Al, 32.76 keV, and 0.914 cGy/R; GE OEC 9900 Elite: 75 kVp, 4.25 mm Al, 46.6 keV, and 0.920 cGy/R. (2) The highest exposure rates measured during clinically implemented protocols for each scanner are as follows: IMRIS VISIUS iCT: 800 mR/hr; Mobis Airo: 6.47 R/hr; Siemens ARCADIS Orbic 3D: 26.4 mR/hr. (3) The effective dose per scan of each device for a full lumbar spine scan are as follows, for normal, overweight, and obese BMI, respectively: IMRIS VISIUS iCT: 12.00 ± 0.30 mSv, 15.91 ± 0.75 mSv, and 23.23 ± 0.55 mSv; Mobius Airo: 5.90 ± 0.25 mSv, 4.97 ± 0.12 mSv, and 3.44 ± 0.21 mSv; Siemens ARCADIS Orbic 3D: 0.30 ± 0.03 mSv, 0.39 ± 0.02 mSv, and 0.28 ± 0.03 mSv; GE OEC 9900 Elite: 0.44 mSv, 0.77 mSv, and 1.14 mSv.
Conclusion:
(1) The IMRIS VISIUS iCT i-Fluoro capable CT scanner and Mobius Airo mobile CT scanner have similar beam characteristics with significantly different tube parameter modulation protocols. Siemens ARCADIS Orbic 3D and GE OEC 9900 offer comparable beam characteristics but different imaging methods. All scanners performed within factory specifications. (2) The IMRIS VISIUS iCT should not be used in i-Fluoro mode for surgical procedures active during scanning due to the 1.42 cGy/s point dose rate in the beam field. The high exposure rate from the Mobius Airo is offset by short scan times and can be mitigated by ensuring enforcement of currently established radiation protection regulations and policies. Minimal stray radiation is measured from the Siemens ARCADIS Orbic 3D. (3) The differences in tube modulation of the CT scanners means the Mobius Airo offers a significantly reduced effective dose with increasing patient BMI over the IMRIS VISIUS iCT. Effective dose from the CT scanners varies as much as one to two orders of magnitude higher than the C Arms, but the Siemens ARCADIS Orbic 3D offers unusable image quality for patients with higher than normal BMI. Based off of physician reported usable surgical image quality of Mobius Airo, this device is recommended for continued integration and implementation during routine surgical procedures for patients of all BMI in orthopedic lumbar spine surgery.
Item Open Access An Investigation of GRID and Spatially Fractionated Radiation Therapy: Dosimetry and Preclinical Trial(2021) Johnson, Timothy RexPurpose: To develop and implement novel methods of extreme spatially fractionated radiation therapy (including GRID therapy) and subsequent evaluation in pre-clinical mice trials investigating the potential of novel radiation treatments with potential for promoting anti-cancer immunogenic response.
Methods: Spatially fractionated GRIDs were designed and precision-milled from 3mm thick lead sheets compatible with mounting on a 225 kVp small animal irradiator (X-Rad). Three pencil-beam GRIDs created arrays of 1mm diameter beams, and three “bar” GRIDs created 1x20mm rectangular fields. GRIDs projected 20x20mm fields at isocenter and beamlets were spaced at 1, 1.25, and 1.5mm, respectively. Output factors, peak-to-valley ratios, and dose distributions were determined with Gafchromic film. The bar GRID with 1mm beamlet spacing (50:50 open:closed ratio) was selected for the pre-clinical trial. Soft-tissue sarcoma (p53/MCA) was transplanted into C57BL/6 mice’s flanks. Four treatment arms were compared: unirradiated control (n=18), conventional radiation therapy (n=16), GRID therapy (n=17), and hemi-irradiation (n=17) where one-half of the beam was blocked. All irradiated mice received a single fraction of 15 Gy to irradiated regions. To date, this is the first study to compare GRID treatment against conventional RT at the same dose.
Results: Very high peak-to-valley ratios were achieved (bar GRIDs: 11.9±0.9, 13.6±0.4, 13.8±0.5; pencil-beam GRIDs: 18.7±0.6, 26.3±1.5, 31.0±3.3). Pencil-beam GRIDs spared twice the number of intra-tumor immune cells as bar GRIDs but left more of the tumor untreated (2-3% vs 14-17% area receiving 95% prescription, respectively). Penumbra was halved when GRIDs were 50% closer to treatment isocenter. The GRID selected for mouse trials was capable of sparing approximately 15% of intra-tumor CD8+ and CD4+ T cells. Preliminary results indicate mean times to tumor quintupling were: 12, 13, 14, and 20 days for unirradiated, GRID, hemi-irradiated, and conventional treatment groups, respectively. To date, all tumors have quintupled except for nine in the AP control group.
Conclusions: Peak-to-valley ratios with kV grids were substantially superior to MV grids, which historically achieve ratios between 2.5 and 6.5. In data collected to date, GRID and hemi-irradiation did not significantly delay tumor growth as compared to an unirradiated control (P = 0.122 and P = 0.2437, respectively, P-values from logrank analysis). Differences between GRID and hemi-irradiation were not statistically significant (P = 0.5257). To date, the AP control group has performed significantly better than all other groups (P<0.001). These results do not corroborate the success of hemi-irradiation in Markovsky et al. 2019. GRID treatments may be more effective if a substantially higher dose and/or multiple fractions were employed.
Item Open Access Chest Phantom Development for Chest X-ray Radiation Protection Surveys, Internal Beta Dosimetry of an Iodine-131 Labelled Elastin-Like Polypeptide, and I-131 Beta Detection Using a Scintillating Nanoparticle Detector(2018) Hyatt, Steven PhilipProject 1: Chest Phantom Development for Chest X-ray Radiation Protection Surveys
Purpose: Develop an acrylic phantom to accurately represent an average adult’s chest for use in radiographic chest unit radiation protection surveys.
Materials and Methods: 6 sheets of 3.81 cm thick acrylic were cut and assembled to form a 30.5 x 30.5 x 20.3 cm hollow box phantom. The acrylic served as tissue equivalent material and the hollow center simulated lungs in a human patient. Six sheets of 1 mm thick aluminum were cut to line the inner walls of the acrylic phantom to potentially boost scatter radiation. Three phantoms underwent posterior-anterior (PA) and lateral chest protocol radiographic scans: the acrylic phantom (with and without the aluminum lining), a 3 gallon water bottle filled with water, and an adult male anthropomorphic phantom. The phantoms were set up as though they were adult patients and scanned with automatic exposure control. Scatter radiation was measured with ion chamber survey meters at 4 points within the room for each phantom and protocol. The scatter data from the acrylic phantom and water bottle were compared to the anthropomorphic phantom to determine which one more accurately represented an adult patient.
Results: For the PA protocol, the average percent difference in measurements between the acrylic phantom and anthropomorphic phantom was 33.3±28.8% with the aluminum lining and 33.0±21.2% without the lining. The percent difference between the water bottle and anthropomorphic phantom was 66.5±42.0%. For the lateral protocol, the average percent difference in measurements between the acrylic phantom and anthropomorphic phantom was 157.6±5.6% with the aluminum lining and 143.0±17.6% without the lining. The percent difference between the water bottle and anthropomorphic phantom was 78.3±22.8%.
Conclusions: The acrylic phantom provided a more accurate comparison to the anthropomorphic phantom than the water bottle for the PA protocol. For the lateral protocol, neither the acrylic phantom nor water bottle provided an adequate comparison to the anthropomorphic phantom.
Project 2: Internal Beta Dosimetry of an Iodine-131 Labelled Elastin-Like Polypeptide
Purpose: Develop a model and simulation to better understand the dosimetry of an I-131 labeled elastin-like polypeptide (ELP) brachytherapy technique.
Materials and Methods: To develop the model, an average scenario based on mouse trials was explored. A 125 mg tumor was approximated as a sphere, with the I-131 ELP injected into its center. The ELP solidifies into a spherical depot – approximately 1/3 the volume of the tumor – and becomes a permanent brachytherapy source. The injected activity of I-131 was 1.25 mCi. I-131 primarily emits β radiation with an average energy of 182 keV, therefore it was determined that all such emissions were confined within the bounds of the tumor. Gamma emissions associated with I-131 were ignored as they were determined to have enough energy to escape the bounds of the tumor without any interaction. This model was implemented into a simulation using the Monte Carlo program FLUKA. From this simulation, the absorbed dose to the tumor and ELP depot, along with the dose profile, was calculated.
Results: The tumor received an absorbed dose of 72.3 Gy while the ELP received 1.14×10^3 Gy. From the dose profile, it was determined that 99% of the absorbed dose to the tumor was highly localized to a 0.3 mm region surrounding the ELP depot.
Conclusions: The model and simulation provided a better understanding of the dosimetry underlying the novel ELP brachytherapy technique. Results obtained demonstrated that the ELP method delivers doses that are comparable to current conventional brachytherapy techniques.
Project 3: I-131 Beta Detection Using a Scintillating Nanoparticle Detector
Purpose: Determine if a scintillating nanocrystal fiber optic detector (nano-FOD) could detect β emissions from I-131.
Materials and Methods: The nano-FOD’s β response was tested using a source vial containing 101 mCi of I-131 in 2 mL of stabilizing solution. A glass vial containing the I-131 was placed inside a lead pig for shielding. A 1 mm diameter hole was drilled through the tops of the vial and pig to allow insertion of the nano-FOD. Measurements were taken every day over a 17 day period by repeatedly submerging the nano-FOD in the I-131 solution and recording the voltage signal it produced. The activity at the time of measurement was calculated based on the time and date of data acquisition. The net signal and signal-to-noise ratio (SNR) were then calculated and plotted as functions of I-131 concentration.
Results: The nano-FOD produced a measurable response when exposed to the β emissions of I-131. The net signal and SNR both demonstrated a linear correlation with the concentration of I-131.
Conclusions: The nano-FOD was demonstrated to be capable of β detection with a linear correlation to activity. If the signals measured can be calibrated to radiation exposure, then the nano-FOD has promising applications as a novel β detector.
Item Open Access Clinical and Research Applications of 3D Dosimetry(2015-01-01) Juang, TitaniaQuality assurance (QA) is a critical component of radiation oncology medical physics for both effective treatment and patient safety, particularly as innovations in technology allow movement toward advanced treatment techniques that require increasingly higher accuracy in delivery. Comprehensive 3D dosimetry with PRESAGE® 3D dosimeters read out via optical CT has the potential to detect errors that would be missed by current systems of measurement, and thereby improve the rigor of current QA techniques through providing high-resolution, full 3D verification for a wide range of clinical applications. The broad objective of this dissertation research is to advance and strengthen the standards of QA for radiation therapy, both by driving the development and optimization of PRESAGE® 3D dosimeters for specific clinical and research applications and by applying the technique of high resolution 3D dosimetry toward addressing clinical needs in the current practice of radiation therapy. The specific applications that this dissertation focuses on address several topical concerns: (1) increasing the quality, consistency, and rigor of radiation therapy delivery through comprehensive 3D verification in remote credentialing evaluations, (2) investigating a reusable 3D dosimeter that could potentially facilitate wider implementation of 3D dosimetry through improving cost-effectiveness, and (3) validating deformable image registration (DIR) algorithms prior to clinical implementation in dose deformation and accumulation calculations.
3D Remote Dosimetry: The feasibility of remote high-resolution 3D dosimetry with the PRESAGE®/Optical-CT system was investigated using two nominally identical optical-CT scanners for 3D dosimetry were constructed and placed at the base (Duke University) and remote (IROC Houston) institutions. Two formulations of PRESAGE® (SS1, SS2) were investigated with four unirradiated PRESAGE® dosimeters imaged at the base institution, then shipped to the remote institution for planning and irradiation. After each dosimeter was irradiated with the same treatment plan and subsequently read out by optical CT at the remote institution, the dosimeters were shipped back to the base institution for remote dosimetry readout 3 days post-irradiation. Measured on-site and remote relative 3D dose distributions were registered to the Pinnacle dose calculation, which served as the reference distribution for 3D gamma calculations with passing criteria of 5%/2mm, 3%/3mm, and 3%/2mm with a 10% dose threshold. Gamma passing rates, dose profiles, and dose maps were used to assess and compare the performance of both PRESAGE® formulations for remote dosimetry. Both PRESAGE® formulations under study maintained high linearity of dose response (R2>0.996) over 14 days with response slope consistency within 4.9% (SS1) and 6.6% (SS2). Better agreements between the Pinnacle plan and dosimeter readout were observed in PRESAGE® formulation SS2, which had higher passing rates and consistency between immediate and remote results at all metrics. This formulation also demonstrated a relative dose distribution that remained stable over time. These results provide a foundation for future investigations using remote dosimetry to study the accuracy of advanced radiation treatments.
A Reusable 3D Dosimeter: New Presage-RU formulations made using a lower durometer polyurethane matrix (Shore hardness 30-50A) exhibit a response that optically clears following irradiation and opens up the potential for reirradiation and dosimeter reusability. This would have the practical benefit of improving cost-effectiveness and thereby facilitating the wider implementation of comprehensive, high resolution 3D dosimetry. Three formulations (RU-3050-1.7, RU-3050-1.5, and RU-50-1.5) were assessed with multiple irradiations of both small volume samples and larger volume dosimeters, then characterized and evaluated for dose response sensitivity, optical clearing, dose-rate independence, dosimetric accuracy, and the effects of reirradiation on dose measurement. The primary shortcoming of these dosimeters was the discovery of age-dependent gradients in dose response sensitivity, which varied dose response by as much as 30% and prevented accurate measurement. This is unprecedented in the standard formulations and presumably caused by diffusion of a desensitizing agent into the lower durometer polyurethane. The effect of prior irradiation on the dosimeters would also be a concern as it was seen that the relative amount of dose delivered to any given region of the dosimeter will affect subsequent sensitivity in that area, which would in effect create spatially-dependent variable dose sensitivities throughout the dosimeter based on the distributions of prior irradiations. While a successful reusable dosimeter may not have been realized from this work, these studies nonetheless contributed useful information that will affect future development, including in the area of deformable dosimetry, and provide a framework for future reusable dosimeter testing.
Validating Deformable Image Registration Algorithms: Deformable image registration (DIR) algorithms are used for multi-fraction dose accumulation and treatment response assessment for adaptive radiation therapy, but the accuracy of these methods must be investigated prior to clinical implementation. 12 novel deformable PRESAGE® 3D dosimeter formulations were introduced and characterized for potential use in validating DIR algorithms by providing accurate, ground-truth deformed dose measurement for comparison to DIR-predicted deformed dose distributions. Two commercial clinical DIR software algorithms were evaluated for dose deformation accuracy by comparison against a measured deformed dosimeter dose distribution. This measured distribution was obtained by irradiating a dosimeter under lateral compression, then releasing it from compression so that it could return to its original geometry. The dose distribution within the dosimeter deformed along with the dosimeter volume as it regained to its original shape, thus providing a measurable ground truth deformed dose distribution. Results showed that intensity-based DIR algorithms produce high levels of error and physically unrealistic deformations when deforming a homogeneous structure; this is expected as lack of internal structure is challenging for intensity-based DIR algorithms to deform accurately as they rely on matching fairly closely spaced heterogeneous intensity features. A biomechanical, intensity-independent DIR algorithm demonstrated substantially closer agreement to the measured deformed dose distribution with 3D gamma passing rates (3%/3mm) in the range of 90-91%. These results underscore the necessity and importance of validating DIR algorithms for specific clinical scenarios prior to clinical implementation.
Item Open Access Effects of High Volume MOSFET Usage on Dosimetry in Pediatric CT, Pediatric Lens of the Eye Dose Reduction Using Siemens Care kV, & Designing Quality Assurance of a Cesium Calibration Source(2017) Smith, Aaron KennethProject 1: Effects of High Volume MOSFET Usage on Dosimetry in Pediatric CT
Purpose
The objective of this study was to determine if using large numbers of Metal-Oxide-Semiconducting-Field-Effect Transistors, MOSFETs, effects the results of dosimetry studies done with pediatric phantoms due to the attenuation properties of the MOSFETs. The two primary focuses of the study were first to experimentally determine the degree to which high numbers of MOSFET detectors attenuate an X-ray beam of Computed Tomography (CT) quality and second, to experimentally verify the effect that the large number of MOSFETs have on dose in a pediatric phantom undergoing a routine CT examination.
Materials and Methods
A Precision X-Ray X-Rad 320 set to 120kVp with an effective half value layer of 7.30mm aluminum was used in concert with a tissue equivalent block phantom and several used MOSFET cables to determine the attenuation properties of the MOSFET cables by measuring the dose (via a 0.18cc ion chamber) given to a point in the center of the phantom in a 0.5 min exposure with a variety of MOSFET arrangements. After the attenuating properties of the cables were known, a GE Discovery 750 CT scanner was employed using a routine chest CT protocol in concert with a 10-year-old Atom Dosimetry Phantom and MOSFET dosimeters in 5 different locations in and on the phantom (upper left lung (ULL), upper right lung (URL), lower left lung (LLL), lower right lung (LRL), and the center of the chest to represent skin dose). Twenty-eight used MOSFET cables were arranged and taped on the chest of the phantom to cover 30% of the circumference of the phantom (19.2 cm). Scans using tube current modulation and not using tube current modulation were taken at 30, 20, 10, and 0% circumference coverage and 28 MOSFETs bundled and laid to the side of the phantom. The dose to the various MOSFET locations in and on the chest were calculated and the image quality was accessed in several of these situations by taking the standard deviation of a large regions of interest in both the lung and the soft tissue of the chest to measure the noise.
Results
The proof of concept experiment found that the main cable of the MOSET, not the ends closest to the reading tip, is the most attenuating part of the cable. The proof of concept also found that increasing the number of MOSFET layers to 1, 2, 3, and 4 layers decreased the dose to the center of the phantom by 17.92, 28.04, 39.98, 42.49% respectively. Increasing the percent of the block phantom covered to 10, 30, and 50% coverage decreased the dose to the center of the phantom by 17.92, 17.80, and 18.17% respectively.
Project 2: Pediatric Lens of the Eye Dose Reduction Using Siemens Care kV
Purpose
The Siemens Care kV is a software that recommends a tube potential (kV) setting for CT scans based on the thickness of the anatomy being scanned in order to reduce dose on a patient to patient basis. Pediatric cranial scans at Duke do not use this software nor do they use tube current modulation. Dose to the lens of the eye in pediatric patients can lead to lens opacity later in life [10]. The goal of this project was to determine if Care kV can be used in pediatric cranial scans to reduce the dose to the lens of the eye while maintaining adequate image quality.
Materials and Methods
A Siemens SOMATOM Force CT scanner performing a routine cranial scan protocol was used in concert with two Atom Dosimetry Phantoms (1-year-old and 5-year-old) and MOSFET dosimeters to determine the effect changing the reference tube potential of the Care kV software would have on dose and image quality (measured with CNR). The settings used with Care kV were off, and semi reference tube potential 120, 110, and 100 kV.
Results
Dose to the lens of the eye was reduced for the 1-year old phantom by 9.601, 17.572, and 19.724% by using Care kV with tube potential set to 120, 110 and 100 kV respectively. Dose to the lens of the eye was reduced for the 5-year old phantom by 1.060, 8.859, and17.854% by using Care kV with tube potential set to 120, 110 and 100 kV respectively. Soft tissue CNR was reduced for the 1-year old phantom by 8.812, 11.001, and 5.018% by using Care kV with tube potential set to 120, 110 and 100 kV respectively. Soft tissue CNR was reduced for the 5-year old phantom by 3.473, 5.517, and 3.248% by using Care kV with tube potential set to 120, 110 and 100 kV respectively. Bone CNR was reduced for the 1-year old phantom by 4.447, 8.175, and 10.046% by using Care kV with tube potential set to 120, 110 and 100 kV respectively. Bone CNR was reduced for the 5-year old phantom by 4.782, 7.966, and 11.715% by using Care kV with tube potential set to 120, 110 and 100 kV respectively.
Project 3: Designing Quality Assurance for Cesium Calibration Source
Purpose
North Caroline regulations state that survey meters must be traceable to NIST. The Cs-137 Calibration source used by Duke was installed in 2005 and has since not been measured except for routine calibration of survey meters. The goal of this project was to measure the geometry and dose rate of the source and make a recommendation as to how and how often quality assurance measurements should be made with a NIST traceable ion chamber.
Materials and Methods
Gafchromic XR QA2 radiochromic film was placed in the source beam to measure the angle of the source collimator. Two 0.18 cc and a 6 cc ion chamber were used in a variety of combinations of distance from source and attenuation to determine the exposure rate of the calibration source and compare it to the current calibration table in use.
Results
The collimator angles for the top, bottom, left, and right were calculated to be 12.13, 9.648, 11.58, and 11.58, respectively. The two 0.18 cc ion chambers deviated from the table values by more than 30% for every measurement. The 6 cc ion chamber deviated from the calibration table in use by 9.55, 8.13, 3.36, and 3.72% for 30 cm no attenuation, 30 cm 2x attenuation, 100 cm no attenuation, and 100 cm 2x attenuation measurements respectively.
Item Open Access Estimating Effective Dose from Phantom Dose Measurements in Atrial Fibrillation Ablation Procedures and Comparison of MOSFET and TLD Detectors in a Small Animal Dosimetry Setting(2011) AndersonEvans, Colin DavidAtrial Fibrillation (AF) is an ever increasing health risk in the United States. The most common type of cardiac arrhythmia, AF is associated with increased mortality and ischemic cerebrovascular events. Managing AF can include, among other treatments, an interventional procedure called catheter ablation. The procedure involves the use of biplane fluoroscopy during which a patient can be exposed to radiation for as much as two hours or more. The deleterious effects of radiation become a concern when dealing with long fluoroscopy times, and because the AF ablation procedure is elective, it makes relating the risks of radiation ever more essential.
This study hopes to quantify the risk through the derivation of dose conversion coefficients (DCCs) from the dose-area product (DAP) with the intent that DCCs can be used to provide estimates of effective dose (ED) for typical AF ablation procedures. A bi-plane fluoroscopic and angiographic system was used for the simulated AF ablation procedures. For acquisition of organ dose measurements, 20 diagnostic metal-oxide-silicon field effect transistor (MOSFET) detectors were placed at selected organs in a male anthropomorphic phantom, and these detectors were attached to 4 bias supplies to obtain organ dose readings. The DAP was recorded from the system console and independently validated with an ionization chamber and radiochromic film. Bi-plane fluoroscopy was performed on the phantom for 10 minutes to acquire the dose rate for each organ, and the average clinical procedure time was multiplied by each organ dose rate to obtain individual organ doses. The effective dose (ED) was computed by summing the product of each organ dose and the corresponding tissue weighting factor from the ICRP publication 103. Further risk calculations were done according to the BEIR VII Phase 2 report to obtain relative and lifetime attributable risks of cancer for an average AF ablation procedure.
The ED was computed separately for the biplane fluoroscopic and angiographic system's `low' and `normal fluoro' automated settings, yielding 27.9 mSv and 45.6 mSv respectively for an average procedure time of88.1 minutes. The corresponding DAP was 48.7 Gy cm2 and 79.1 Gy*cm2 for low and normal settings respectively. The independently measured DAP was found to be within 0.1 % of that measured by the fluoroscopy system's onboard flat panel detectors. DCCs were calculated to be 0.573 and 0.577 for the respective low and normal settings. The results proved to be very closely matched, which was to be expected. However, the results are higher than some other published DCCs for the same type of procedure. The calculated cancer risks were fairly low due to the age of most patients (less than 5 excess incidents of cancer per 100,000 exposed for stomach colon liver; incidence of lung cancers estimated at 130-300 per 100,000 exposed), but concern remains that longer procedures could increase the risk of erythema or other serious skin injuries.
The second section of this thesis study involves the quantification and distribution of radiation dose in small animals undergoing irradiation in a orthovoltage x-ray unit. Extensive research is being done with small animals, particularly mice and rats, in fields such as cancer therapy, radiation biology and radiological countermeasures. Results and conclusion are often drawn from research based solely on manufacturer's specifications of the delivered dose rate without independent verification or adequate understanding of the machines' capabilities. Accurate radiation dose information is paramount when conducting research in this arena.
Traditional methods of dosimetry, namely thermoluminescence dosimeters (TLDs) are challenging and often time consuming. This section hopes to show that in place of TLDs, MOSFETs can provide accurate, precise dose information comparable with TLDs and ionization chambers. Measurements of all three dosimeters are compared in a small animal irradiator in phantoms and in vivo. Measurements done with MOSFETs are shown to deviate by 2.5% from that of the ADCL calibrated ionization chamber while TLDs showed a 7% deviation. Dose distributions within a phantom are also measured using radiochromic film to estimate the attenuation and show that dose is not uniform throughout the mouse. A dose decrease of approximately 30% is observed in a water phantom, which was only slightly mitigated by a hardening the beam with additional filtration. A Bland-Altman plot was created to show that the MOSFETs and TLDs used to make the dose measurements are statistically equivalent. The results show that all measurements made over a range of doses fall within 1.96 standard deviations of the mean.
Item Open Access Improvements in Small Animal Dosimetry: CIX3 Irradiator Characterization, Novel Phantom Investigation, and Shepherd Cs-137 Irradiator Dose Uniformity Analysis(2023) Filip, Kevin TProject 1 (Chapter 2): X-Strahl CIX3 CharacterizationPurpose: In Fall 2021 Duke University purchased an Xstrahl CIX3 Cabinet Xray Irradiator. A characterization of this machine was performed to determine its dosimetry characteristics and best practices for radiobiological studies at Duke. Basic irradiator acceptance tests were expanded on to fully characterize this new machine. Two unique aspects of this machine were of particular interest. First a unique (non-uniform) filter design was investigated to determine if it has unintended side effects on field conformity. Second the lack of accessible cable ports made thermoluminescent dosimeters (TLDs) the primary dosimeters for experiments. For this reason additional investigations were conducted characterizing TLDs. Materials and Methods: To assess the dosimetric properties of this new machine the following parameters were investigated: output consistency, beam quality, field uniformity, and exposure rates. Output consistency was measured by comparing expected and observed max energy in kVp using a Piranha X-ray multimeter. Beam quality was measured as half value layer of aluminum and compared to expected results from Spekcalc. Spekcalc was used to determine energy fluence and mean energy of the spectrum. Field uniformity was assessed using Gafchromic ™ EBT3 film on an Epson Expression 10000 XL scanner with lateral response artifact correction factors and film calibrated using a NIST traceable 0.18 cc ion chamber. Exposure rates were characterized using a NIST traceable 0.18cc ion chamber and varying filtration, tube energy (kVp), and tray position for all available configurations. TLD energy response, positional response, and batch correction factor techniques were characterized on this machine. Energy response was determined by irradiating TLD’s to a range of energies (70-300 kVp) and the charge response reliv ative to the exposure (50 R) received was determined. Positional response in the field was investigated using the Duke Radiation Dosimetry Laboratory (DRDL) TLD holder and Gafchromic ™ EBT3 film. The relative exposure each TLD received was determined and compared to the ion chamber exposure. Results: The CIX3 had consistent energy output as measured by max energy conformance. The average difference from input voltage to output voltage was 0.84 % with the worst being 1.6 % (150 kVp, 1 mm copper Filtration). Theoretical estimations (Spekcalc) of the beam quality had good agreement with measured half value layers (using Piranha) with an average difference of 1.36 % and worst error of 2.99 % across the energy ranges sampled (50-150 kVp). Field uniformity results indicated general conformance to machine data (90 % within 25.9 cm diameter field) but some non-uniformities were identified. Areas of higher dose (105-110%) relative to the center were observed in the upper right quadrant of the field (from beam eye perspective). TLD energy response followed expected over-response in lower energy ranges, reducing to a normal response as energy increases. The highest over response was at 70 kVp, a 15 % over response compared to 300 kVp (the max energy of the CIX3). The film study to determine TLD positional response determined there were unequal exposures to the 50 TLDs. The trend observed an increase in exposure consistent with the field uniformity results in which the dose relative to the center of the field increased by 5-10 % towards the upper right quadrant. This effect was more pronounced at the lower energy level sampled (90 kVp). Conclusions: The full characterization of the CIX3 was very important to understand the nuances of the new machine. Conformance in beam quality results gave good indications that the machine is operating as designed and radiobiological studies expect to have consistent results between experiments under like conditions. The unique field uniformity results observed could help inform future experimental planning. More importantly it is an extremely important finding for TLD dose calibration. Since TLDs experience at most 6-7 % over exposure compared to the ion chamber it is important to use these findings in future calibrations. Project 2 (Chapter 3): Dose Depth of Small AnimalWater Phantom Purpose: Much is understood about the midpoint dose estimation of small animal phantoms and it has been the focus of DRDL to conduct dosimetry using this value. However, little data was available on the dose depth profile of small animal phantoms. This investigation sought to fill in that dose depth data, compare doses under varying experimental conditions in order to fully understand how the dose is distributed along the beam axis for small animal phantoms. Materials and Methods: A small animal water phantom (50 cc water vial) was characterized on the CIX3 using Gafchromic ™ EBT3 film. Film was calibrated using a NIST traceable 0.18 cc ion chamber. The phantom was irradiated with strips of film (15 total) varying filtration and whether a backscatter plate (uniform piece of acrylic) was included. The film was scanned and analyzed using Film QA software and aggregated dose depth profiles were determined using R Studio and Excel. Results: The dose depth of the phantom was characterized with a coefficient of variation of about 2-3 % across all depths and configurations. The inclusion of the backscatter plate improved the dose uniformity by an average of 2.14 % with most improvements coming from the bottom half of the phantom (closest to the backscatter plate). Average dose rates under each configuration were determined. The midpoint dose rate was found to have good conformance (within 0.5%) to the averaged dose rate across the depth. The dose rate increased by 33 % when using the backscatter plate due to the increased backscatter spectrum and the inverse square law effects. Conclusions: This data gave increased certainty in using the midpoint dose as a surrogate measure for whole body dose averages in small animal phantoms. The improvement in dose uniformity when using the backscatter plate seems like a promising addition to future experimental configurations. However in application the size of the backscatter plate makes it unusable for large experiment samples and it should be implemented only in specific studies as determined during the dosimetry consult with DRDL. Project 3 (Chapter 4): Novel Mouse Phantom Investigation Purpose: In recent years DRDL developed a novel mouse phantom based on feedback from researchers. This novel phantom flattened the mouse to mimic a mouse laying on an irradiation platform, especially when sedated. This investigation sought to determine if the novel ’flat’ phantom made of polymethyl methacrylate (acrylic) (PMMA) had a significant difference in dosimetry when compared with a standard cylindrical phantom made of soft tissue equivalent material. Materials and Methods: To compare the dosimetric differences each phantom a FLUKA Monte Carlo simulation was compared with experimental results from TLDs on the CIX3. In the simulation the dose was compared using a midpoint dose volume. In the experimental design TLDs were used to determine the dose at the midpoint of each phantom. The dose rates were analyzed and compared to determine if there was a significant difference. Results: The Monte Carlo results indicated there were very slight differences between phantom rates. The cylinder phantom had a dose rate of 1.83±0.038 Gy/min while the flat phantom had a midpoint dose of 1.81 ± 0.045 Gy/min, 1.1 percent lower than the cylindrical phantom. An unpaired t-test was performed to determine if the samples were different and was found to give a p-value of 0.71 which gives a high probability that the sampled data are not significantly different. The experimental results were found to be similar. The cylinder phantom had a dose rate of 1.77 ± 0.05 Gy/min while the flat phantom had a midpoint dose of 1.81 ± 0.045 Gy/min, 2.25 percent higher than the cylindrical phantom. Again a t-test was performed and these were determined to not be significantly different (p = 0.31). Conclusions: The flat phantom therefore is very similar to the dosimetry found in the cylinder phantom. Small variations due to material properties, height of phantom, scatter material, and attenuating material all balanced out to provide dosimetry properties that are similar. This means that the cheaper to manufacture flat phantom is just as good as the much more expensive cylinder phantom and both can be used for small animal dosimetry. Project 4 (Chapter 5): Shepherd Mk I - 68A Dose Uniformity Purpose: In 2009 a study was conducted to determine the dose uniformity in a Shepherd Mk I-68A Cs-137 irradiator. Since then vast improvements have been made on film design and software to analyze scanned film with improved accuracy. A follow up study was designed to revisit this previous characterization and update the dose uniformity of the irradiator cavity using these new dosimeters and techniques. Materials and Methods: Gafchromic ™ EBT3 film was calibrated using a NIST traceable 0.18 cc ion chamber on the Shepherd irradiator in each of the three positions available. Large film sheets were then irradiated in a 2 mm acrylic holder in all positions under rotating and non-rotating configurations. The scanned film was analyzed using FilmQA software, R studio, and Excel to determine the dose uniformity relative to the dose in the center. Results: An ion chamber sample was compared to the film results and found to be in good agreement (within 1 %) which indicated the film was appropriately irradiated, scanned, and calibrated. Rotating dose distributions in positions 2 and 3 were nearly equivalent to manufacturer predicted isodose distributions with noted discrepancies at the edges of the field. At a height of 15 cm to achieve dose uniformity of 100 % ± 5 % the rotating tray has a usable radius of 7 cm from the center in position 2 and 8 cm in position 3. Stationary dose distributions were compared to previous uniformity and found to be in general agreement in the center. However the isodose mapping previously characterized did not include a scanner lateral response artifact correction factor which indicated a better uniformity than what was found in this experiment. Position 1 results were similar to previous dose distributions and most importantly confirmed the positioning of the source in the chamber. Conclusions: The updated dose uniformity data provides QA feedback as part of a larger dosimetry program for Duke University. These results indicated that this irradiator was and still is performing as expected and no mechanical failures have caused a source to become misaligned or any major changes to the expected dosimetry.
Item Open Access Investigation of High Resolution 3D Rodent-morphic Dosimetry, and Cost-Effective Optical-CT using Fresnel Lenses(2014) Bache, StevenMicro-irradiators enable exploration of the efficacy of novel radiation treatment approaches by providing the capability to reproduce realistic treatment delivery in small animal models. An approach of current topical interest is hypofractionated stereotactic body radiation therapy (SBRT), and the study of associated tumor and normal tissue radio-biology. Rodent SBRT is extremely challenging, requiring the precise delivery of radiation beams on the order of several millimeters. At present there are no methods to comprehensively verify these delivery techniques due to the requirements for ultra-high resolution and ability to measure the dose in 3 dimensions (3D).
This work introduces a potential solution to the rodent SBRT verification challenge: radiochromic rodent-morphic 3D dosimeters compatible with ultra-high resolution optical computed tomography (optical-CT) dose read-out. Rodent-morphic dosimeters were produced by 3D-printing molds of rodent anatomy directly from X-ray CT data, and using these molds to create tissue-equivalent phantoms both with and without high-Z spinal inserts for cone-beam CT targeting. Feasibility was evaluated through a series of irradiations, including a 180-degree spinal arc treatment. Dose distributions were measured in high-resolution (0.5mm isotropic voxels) with an in-house built optical-CT system, which determined dose from the change in optical density throughout the dosimeters from pre-and post-irradiation scans. Optical-CT data was calibrated to absolute dose using a calibration curve determined from irradiating small volumes of radiochromic material from the same batch as the rodent-morphic dosimeters to known doses in a 6MV beam (negligible energy response was assumed). Independent verification of absolute dose at a point was made with a novel scintillator comprised of europium and lithium doped yttrium oxide nanocrystals, with a sub-mm active length. Independent verification of the dose distribution was performed using EBT2 radiochromic film positioned in the dosimeters, which had been sliced in half. Contrast-to-noise ratio between high-Z spinal inserts and tissue-equivalent PRESAGE material was found to be ~10, sufficient for bony alignment and isocenter targeting with on-board CBCT image guidance. Absolute dose calculated at isocenter through optical-CT was found to agree with nano-detector measurement within 3%, while relative dose distributions in two orthogonal planes were found to agree with film within 4%. PRESAGE rodent-morphic dosimeters demonstrated much promise in the verification of precise radiation treatment given by the X-Rad 225Cx micro-irradiator.
Practical challenges involved in optical-CT imaging were addressed through the investigation of an in-house Fresnel-based optical-CT system with considerably less refractive index-matching fluid. The "DFOS" (Duke Fresnel-based Optical-CT System) system differed from current optical-CT systems by replacing cumbersome convex telecentric lenses with a lighter and much less expensive Fresnel system. A second major modification was the replacement of the refractive index-matching fluid bath with a solid polyurethane tank. PRESAGE radiochromic dosimeters were irradiated with orthogonal parallel-opposed treatments and a brain IMRT treatment and dose distributions were readout by the DFOS system and compared to both treatment planning software prediction and other in-house optical-CT systems. Gamma index passing rate at the 3%/3mm threshold for the two parallel-opposed and brain IMRT treatments were 89.3%, 92.1%, and 87.5%, respectively. The DFOS system showed promise for 3D dosimetry, but the performance is still substantially inferior at present to the gold-standard systems.
Item Open Access Investigation of Presage 3D Dosimetry as a Method of Clinically Intuitive Quality Assurance and Comparison to a Semi-3D Delta4 System(2015) Crockett, EthanThe need for clinically intuitive metrics for patient-specific quality assurance in radiation therapy has been well-documented (Zhen, Nelms et al. 2011). A novel transform method has shown to be effective at converting full-density 3D dose measurements made in a phantom to dose values in the patient geometry, enabling comparisons using clinically intuitive metrics such as dose-volume histograms (Oldham et al. 2011). This work investigates the transform method and compares its calculated dose-volume histograms (DVHs) to DVH values calculated by a Delta4 QA device (Scandidos), marking the first comparison of a true 3D system to a semi-3D device using clinical metrics. Measurements were made using Presage 3D dosimeters, which were readout by an in-house optical-CT scanner. Three patient cases were chosen for the study: one head-and-neck VMAT treatment and two spine IMRT treatments. The transform method showed good agreement with the planned dose values for all three cases. Furthermore, the transformed DVHs adhered to the planned dose with more accuracy than the Delta4 DVHs. The similarity between the Delta4 DVHs and the transformed DVHs, however, was greater for one of the spine cases than it was for the head-and-neck case, implying that the accuracy of the Delta4 Anatomy software may vary from one treatment site to another. Overall, the transform method, which incorporates data from full-density 3D dose measurements, provides clinically intuitive results that are more accurate and consistent than the corresponding results from a semi-3D Delta4 system.
Item Open Access Investigations into the Feasibility of Optical-CT 3D Dosimetry with Minimal Use of Refractively Matched Fluids(2014) Chisholm, KelseyPurpose: Optical-CT imaging with radiochromic dosimeters is a powerful method of evaluating 3D dose distributions at high resolution and sensitivity. Current optical-CT systems require large quantities of refractively matched fluid surrounding the dosimeter in order to minimize refraction artifacts. The use of a refractively matched solid polyurethane solid-tank, in place of a fluid bath, has the potential to greatly increase practical convenience, reduce cost, and improve the efficacy of flood corrections. This thesis aims to investigate the feasibility of solid-tank optical-CT imaging for 3D dosimetry, and to use computer simulation to investigate optimal design and scanning parameters.
Methods: A Matlab based ray-tracing simulation platform, ScanSim, was used to model a parallel-source imaging system through a cubic polyurethane solid-tank containing a central cylindrical hollow into which cylindrical PRESAGE® radiochromic dosimeters can be placed. A small amount of fluid surrounds the dosimeter in the tank. ScanSim's capabilities were expanded from previous work to include the geometry and physics of dry scanning. Two imaging methods were investigated, representing a telecentric detector and an ideal detector: in the latter, all light rays are collected and used in reconstruction. In order to characterize the efficacy of these systems, and dependence on refractive index (RI) mismatches between dosimeter, solid-tank, and fluid, simulations were run for a variety of dosimeter (RI = 1.5-1.47), and fluid (RI = 1.55-1.0) combinations. Additional simulations examined the effect of increasing gap size (1-5mm) between the dosimeter and solid-tank well. For the telecentric setup, the effects of changing the lens tolerance (0.5-5.0 degrees) were also investigated. The metric for evaluation of efficacy is the usable radius, which is defined as the distance from the dosimeter center where the measured and true (known) dose differs by less than 2%.
Results: As the refractive index mismatch between the dosimeter and tank increases from 0-0.02, the telecentric system showed a significant decrease in the usable radius from 97.6% to 50.2% compared to a decrease from 97.6% to 96.4% for the ideal system. When the three media are perfectly matched, the telecentric system and ideal system perform identically. For mismatched dosimeter and solid-tank in a telecentric system, the optimal fluid match has a refractive index lower than either the tank or dosimeter, decreasing non-linearly from 1.5-1.34 as the dosimeter-tank refractive mismatch increases from 0 to 0.02. Media mismatches between the dosimeter and solid-tank also exacerbate the effects of changing the gap size, with no apparent quantifiable relationship. Generally, the optimal fluid match is closer to the dosimeter RI when the gap size is large (>3mm). Increasing the telecentric lens tolerance improves the usable radius for all refractive media combinations, and approaches the behavior of the ideal system for tolerances >5.0°.
Item Open Access Monte Carlo Analysis and Physics Characterization of a Novel Nanoparticle Detector for Medical and Micro-dosimetry Applications(2015) Belley, Matthew DavidThe outcomes for both (i) radiation therapy and (ii) preclinical small animal radio- biology studies are dependent on the delivery of a known quantity of radiation to a specific and intentional location. Adverse effects can result from these procedures if the dose to the target is too high or low, and can also result from an incorrect spatial distribution in which nearby normal healthy tissue can be undesirably damaged by poor radiation delivery techniques. Thus, in mice and humans alike, the spatial dose distributions from radiation sources should be well characterized in terms of the absolute dose quantity, and with pin-point accuracy. When dealing with the steep spatial dose gradients consequential to either (i) high dose rate (HDR) brachytherapy or (ii) within the small organs and tissue inhomogeneities of mice, obtaining accurate and highly precise dose results can be very challenging, considering commercially available radiation detection tools, such as ion chambers, are often too large for in-vivo use.
In this dissertation two tools are developed and applied for both clinical and preclinical radiation measurement. The first tool is a novel radiation detector for acquiring physical measurements, fabricated from an inorganic nano-crystalline scintillator that has been fixed on an optical fiber terminus. This dosimeter allows for the measurement of point doses to sub-millimeter resolution, and has the ability to be placed in-vivo in humans and small animals. Real-time data is displayed to the user to provide instant quality assurance and dose-rate information. The second tool utilizes an open source Monte Carlo particle transport code, and was applied for small animal dosimetry studies to calculate organ doses and recommend new techniques of dose prescription in mice, as well as to characterize dose to the murine bone marrow compartment with micron-scale resolution.
Hardware design changes were implemented to reduce the overall fiber diameter to <0.9 mm for the nano-crystalline scintillator based fiber optic detector (NanoFOD) system. Lower limits of device sensitivity were found to be approximately 0.05 cGy/s. Herein, this detector was demonstrated to perform quality assurance of clinical 192Ir HDR brachytherapy procedures, providing comparable dose measurements as thermo-luminescent dosimeters and accuracy within 20% of the treatment planning software (TPS) for 27 treatments conducted, with an inter-quartile range ratio to the TPS dose value of (1.02-0.94=0.08). After removing contaminant signals (Cerenkov and diode background), calibration of the detector enabled accurate dose measurements for vaginal applicator brachytherapy procedures. For 192Ir use, energy response changed by a factor of 2.25 over the SDD values of 3 to 9 cm; however a cap made of 0.2 mm thickness silver reduced energy dependence to a factor of 1.25 over the same SDD range, but had the consequence of reducing overall sensitivity by 33%.
For preclinical measurements, dose accuracy of the NanoFOD was within 1.3% of MOSFET measured dose values in a cylindrical mouse phantom at 225 kV for x-ray irradiation at angles of 0, 90, 180, and 270˝. The NanoFOD exhibited small changes in angular sensitivity, with a coefficient of variation (COV) of 3.6% at 120 kV and 1% at 225 kV. When the NanoFOD was placed alongside a MOSFET in the liver of a sacrificed mouse and treatment was delivered at 225 kV with 0.3 mm Cu filter, the dose difference was only 1.09% with use of the 4x4 cm collimator, and -0.03% with no collimation. Additionally, the NanoFOD utilized a scintillator of 11 µm thickness to measure small x-ray fields for microbeam radiation therapy (MRT) applications, and achieved 2.7% dose accuracy of the microbeam peak in comparison to radiochromic film. Modest differences between the full-width at half maximum measured lateral dimension of the MRT system were observed between the NanoFOD (420 µm) and radiochromic film (320 µm), but these differences have been explained mostly as an artifact due to the geometry used and volumetric effects in the scintillator material. Characterization of the energy dependence for the yttrium-oxide based scintillator material was performed in the range of 40-320 kV (2 mm Al filtration), and the maximum device sensitivity was achieved at 100 kV. Tissue maximum ratio data measurements were carried out on a small animal x-ray irradiator system at 320 kV and demonstrated an average difference of 0.9% as compared to a MOSFET dosimeter in the range of 2.5 to 33 cm depth in tissue equivalent plastic blocks. Irradiation of the NanoFOD fiber and scintillator material on a 137Cs gamma irradiator to 1600 Gy did not produce any measurable change in light output, suggesting that the NanoFOD system may be re-used without the need for replacement or recalibration over its lifetime.
For small animal irradiator systems, researchers can deliver a given dose to a target organ by controlling exposure time. Currently, researchers calculate this exposure time by dividing the total dose that they wish to deliver by a single provided dose rate value. This method is independent of the target organ. Studies conducted here used Monte Carlo particle transport codes to justify a new method of dose prescription in mice, that considers organ specific doses. Monte Carlo simulations were performed in the Geant4 Application for Tomographic Emission (GATE) toolkit using a MOBY mouse whole-body phantom. The non-homogeneous phantom was comprised of 256x256x800 voxels of size 0.145x0.145x0.145 mm3. Differences of up to 20-30% in dose to soft-tissue target organs was demonstrated, and methods for alleviating these errors were suggested during whole body radiation of mice by utilizing organ specific and x-ray tube filter specific dose rates for all irradiations.
Monte Carlo analysis was used on 1 µm resolution CT images of a mouse femur and a mouse vertebra to calculate the dose gradients within the bone marrow (BM) compartment of mice based on different radiation beam qualities relevant to x-ray and isotope type irradiators. Results and findings indicated that soft x-ray beams (160 kV at 0.62 mm Cu HVL and 320 kV at 1 mm Cu HVL) lead to substantially higher dose to BM within close proximity to mineral bone (within about 60 µm) as compared to hard x-ray beams (320 kV at 4 mm Cu HVL) and isotope based gamma irradiators (137Cs). The average dose increases to the BM in the vertebra for these four aforementioned radiation beam qualities were found to be 31%, 17%, 8%, and 1%, respectively. Both in-vitro and in-vivo experimental studies confirmed these simulation results, demonstrating that the 320 kV, 1 mm Cu HVL beam caused statistically significant increased killing to the BM cells at 6 Gy dose levels in comparison to both the 320 kV, 4 mm Cu HVL and the 662 keV, 137Cs beams.
Item Embargo Monte Carlo Investigation of Dosimetry Under Partial Transmission Blocks in Total Body Irradiation Treatment(2023) Li, PeixiongPurpose: Total body irradiation (TBI) is commonly performed using opposing photon beams of maximum field size at extended SSD. Partial transmission blocks (PTB) are utilized to shield critical organs such as the lungs and kidneys. Both phantom measurement and convolution algorithms confirmed that PDD under PTB deviates significantly from those regions without the blocks. The relationship is complex and depends on many factors. In this study, we investigated the dosimetry under the PTB using the Monte Carlo tool.Methods: The photon phase space (PSP) for Truebeam linac from MyVarian was used as input in the EGSnrc package. The PSP was analyzed and separated into primary (originating from the target) and scatter ( extra-focal source originating from flattening filter) components. It was hypothesized that they behave differently in the presence of PTB which is responsible for the uncommon dosimetry. In this study, a virtual filter was developed to simulate the PTB of any transmission factors in EGSnrc. Further, a concept of scatter photon enhancement ratio (SPER=〖scatter〗_PTB/(〖primary〗_PTB+〖scatter〗_PTB )/〖scatter〗_open/(〖primary〗_open+〖scatter〗_open ) ) was proposed to quantify how the scatter photons’ dose contribution changes with SSD, block size, block-to-patient distance, and transmission factor. Results: Scatter accounts for 12% for 6X, but only 5% for 6XFFF. MC result of the virtual PTB filter agrees well with the measurement for PDD (<1.5%). For a clinical PTB of size 6x12 cm2 at the surface, the SPER at 5cm depth increases from 2.01 to 3.27 when SSD 100 to 400cm; decreases from 3.38 to 1.09 when block-surface-distance 15010cm; and decreases from 8.38 to 2.60 when PTB transmission factor 0 to 30%. Conclusion: The dosimetry under PTB for TBI can be explained by the different behavior of the primary and scatter photon components. MC allows the separation and independent investigation of each component. For in vivo dose measurement under PTB, the measurement needs to be interpreted carefully using the correct dosimetry.
Item Open Access Neutron Dosimetry of Mice Using Monoenergetic Neutron Beams(2011) Fallin, Brent AlanIn 2009 the researchers at Triangle Universities Nuclear Laboratory (TUNL) participated in a series of experiments with the Radiation Countermeasures Center of Research Excellence (RadCCORE). This thesis project is a component of the research done at TUNL that was partially supported by the RadCCORE collaboration. The primary goals of this work are: (1) to measure the neutron fluence (and hence the dose) from the standard neutron beam source at TUNL delivered to a small animal target to an accuracy of better than ± 10% and (2) to develop techniques for real time monitoring of the absolute dose delivered to small animal targets from neutron beam irradiation. These two projects are interconnected as the development of the real-time monitoring techniques depends on the results of the absolute fluence measurements.
Measuring the absolute neutron beam fluence necessitates the use of a reaction in which the neutron cross section is accurately known over the relevant energy range and a detection technique which is insensitive to gamma-rays or is capable of distinguishing gamma-rays from neutrons. In this work, neutron activation of aluminum and gold foils was used to make absolute measurements of the fast neutron (En ~ 10 MeV) fluence. Neutron activation of gold foils was also used to make a relative measurement of the thermal neutron fluence. The neutrons produced nuclear reactions in the foils, converting a small quantity of the stable atoms in the foils into radioactive ones which subsequently generate gamma-rays in their decay process. The activated foils are then removed from the beam and placed in front of a high-purity germanium (HPGe) detector that measures the energy spectrum of the gamma-rays emitted by the foil. By counting the number of gamma-rays detected over a set time, the incident neutron fluence at the foil location was determined using the known reaction cross sections. The measured neutron fluence was used to calculate the imparted dose to live mouse targets via the muscle tissue neutron kerma factors. Liquid and plastic scintillation detectors were also used to monitor the relative neutron flux in real time during the experiments. These relative detectors were subsequently calibrated using flux results obtained from the foil activation measurements and were used for real time dose monitoring.
The neutron beam produced at TUNL also has an intrinsic gamma component that adds to the dose received by a small animal target. The gamma contribution to imparted dose is generally taken to be around 10% or less for neutron beams created by linear accelerators utilizing the 2H(d,n)3He reaction, but no confirming measurements of this type have been performed at TUNL prior to this work. To verify this claim, an experiment was conducted to quantify the gamma-ray contribution to the target dose at several incident neutron energies and gas cell pressures.
The dosage from the mixed beam was measured using two ionization chambers that have different sensitivities to neutron and gamma radiation. The chambers were placed in the neutron beam, and the total charge induced in the ionization chamber by the mixed radiation field was monitored. The percent gamma-ray contribution to total target dose was calculated utilizing the procedures outlined in AAPM Report No. 7 and Attix.
Using the foil activation technique, the neutron fluence incident on target and dose delivered were measured to within ± 10%. The target dose estimated using the scintillation detectors was found to be accurate to within ± 20%. The results of the ion chamber measurements imply the gamma-ray component of the neutron beam at TUNL contributes less than 5% to the total target dose. Given the large difference in quality factors between gamma-rays (=1) and fast neutrons (~10), the contribution by gamma radiation to the total equivalent dose was determined to be negligible.
Item Open Access Neutron Stimulated Emission Computed Tomography: Optimization of Acquisition Parameters Using Resolution and Dosimetry in the Context of Liver and Breast Cancers(2013) Raterman, Gretchen MaryProposed is a method for investigating optimal acquisition parameters in NSECT, neutron stimulated emission computed tomography, for good image quality and low dose for diagnosing liver and breast cancers. These parameters include the number of angles, number of translations per angle, beam width, and beam width spacing. These parameters will affect dose, which will increase with increasing total neutron flux. Therefore, a balance must be achieved for the parameters mentioned above, to yield a desired dose limit and tolerable spatial resolution necessary for liver and breast cancer diagnosis.
Using Monte Carlo simulation toolkit GEANT4, the effects of beam spread due to neutron elastic scatter was explored. Then, a geometrical water torso phantom with slanted edge solid iron phantom was run for different acquisition parameters, and an MTF was taken to determine resolution for each set. For dose considerations, two anthropomorphic voxelized phantoms, one with liver cancer lesions, and one with breast cancer lesions, were scanned with the same parameter sets, and organ doses and DVHs, dose volume histograms, was computed for each set. In addition, images of the phantom in the lesion plane were reconstructed for those parameter sets showing best resolution and lowest dose.
It is found that beam spread due to elastic scatter off of Hydrogen atoms is negligible for all beam widths. For optimal resolution in the primary breast phantom, it was found that acquisition parameters of a 5 mm beam, with no gaps, with any of the five angles provided the superior resolution. For the optimal resolution in the liver, it was found that down sampling angles and introducing gaps between projections greatly affected image accuracy and resolution. Also, the 5 mm beam width provided better geometrical accuracy, but the 1 cm bream width provided slightly better resolution.
Organ doses are computed for the primary organ and organs at risk for each parameter set at 500 K neutrons per projection. For a scan of the full volume of the liver, liver organ doses ranged from 25.83 to 0.19 mSv. For the same scan, the organ doses for the heart ranged from 0.18 to 0.05 mSv. For a scan with the same pool of acquisition parameters of the full volume of the breast, breast organ doses ranged from 49.87 to 0.38 mSv. Furthermore, the DVHs for both scans showed a very steep drop-off at low dose bins for secondary organs at risk and a reasonable drop-off for the primary organ.
In choosing the optimal acquisition parameters using both resolution and dose, a metric equal to resolution times dose is used, in which low values are optimal. An upper threshold for the metric was chosen based on dose values in currently used medical imaging modalities. A pool of optimal parameter sets was then identified using the metric. To further identify the optimum, a metric estimating geometrical accuracy of the reconstructed square was used. For the breast scan, the optimal parameter set was a 1 cm beam width, with 0 mm a gap, with 12 angles. For the liver scan, the optimal parameter set was a 1 cm beam width, with a 0 mm gap, with 36 angles.
Finally, reconstructed images of the anthropomorphic scans using the super sampled geometry in the liver scan showed one lesion, using images of iron and phosphorous. With more degraded image quality, reconstructed images of the breasts using the super sampled geometry showed only the three cm lesion accurately. The images reconstructed from the optimal set identified for liver scans also showed the larger lesion, except with some noise from the presence of iron and phosphorous in other organs. The images reconstructed from the optimal set identified for the breast scans had a similar result to that of the super-sampled case, albeit with lower contrast. The least sampled case for both scans were found to be diagnostically useless. From these anthropomorphic images, this work demonstrates that in-vivo imaging of breast and liver cancers may be potentially possible with NSECT at a low dose.
Item Open Access Organ Localization: Moving Toward Patient Specific Prospective Organ Dosimetry for CT(2012) Rybicki, KevinPurpose: Radiation doses from computed tomography (CT) examinations have come under public and governmental scrutiny because of several recent misadministrations of radiation across the country. Current CT dosimetry methods in the clinic use standardized cylindrical water phantoms to measure radiation dose across various scanning protocols and different scanner manufacturers. These methods and equipment are too generalized to provide accurate risk assessment for patients of varying ages, genders, and anatomies. The advent of computer models based on real CT imaged anatomy has made patient specific and organ specific dosimetry achievable.
With a population of both pediatric and adult patient models comprised of a wide range of anatomies, Monte Carlo based dose calculations can be cataloged. A patient can receive a prospective dose estimation from a phantom within our population that best exhibits the patient's age and anatomical characteristics. Knowledge of organ size and location is essential to finding a proper match between the patient and the computer model. To this end, very little information is currently available regarding organ size and location across a diverse human population. The purpose of this study was to develop a predictive model to ascertain organ locations and volumes for pediatric and adult patients.
Methods: This study included 51 adults and 40 pediatrics from which Extended NURBS-based Cardiac-Torso (XCAT) phantoms were generated. Large organs were manually segmented from clinical CT data. The remaining organs and other anatomical structures were created by transforming an existing human model template to fit the framework of the segmented structures. The maximum and minimum points of the organs were recorded with respect to the axial distance from the tip of the sacrum. The axial width and midpoint for each organ were then determined. The organ volumes were also calculated. All three organ parameters were plotted as functions of patient age and weight for adults and patient age for pediatrics.
Results: The adult patients showed no statistically significant correlation between organ parameters and age and BMI. There were slight, positive linear trends with organ midpoint (max r2=0.365, mean r2=0.185) and organ volume (max r2=0.510, mean r2=0.183) versus adult patient weight. The height correlations were also positive for midpoint (r2=0.485, mean r2=0.271). Gaussian fits performed on probability density functions of adult organs resulted in r2-values ranging from 0.945 to 0.996. Pediatric patients demonstrated strong cube root relationships with organ midpoints (max r2=0.857, mean r2=0.790) and organ widths (max r2=0.905 , mean r2=0.564) versus age. Pediatric organ volumes showed positive linear relationships versus age (max r2=0.983, mean r2=0.701).
Conclusions: Adult patients exhibited small variations in organ volume and location with respect to weight, but no meaningful correlation existed between these parameters and age. Once adulthood is reached, organ morphology and positioning seems to remain static; however, clear trends are evident between pediatric age and organ volumes and locations. Such information can aid in the selection of an appropriate computer model that has the highest probability of mirroring the anatomy of a patient undergoing a clinical exam. Applications could also extend into comparing PET versus CT determination of organ volume and location.
Item Open Access Synthesis, Characterization, and Spectroscopy of Lanthanide-Doped Inorganic Nanocrystals; Radiant Flux and Absolute Quantum Yield Measurements of Upconversion Nanocrystals, and Fabrication of a Fiber-Optic Radiation Detector Utilizing Synthetically Optimized, Linearly Responsive Nanoscintillators(2013) Stanton, Ian NicholasThe ability to interrogate structure-function photophysical properties on lanthanide-doped nanoscale materials will define their utility in next-generation applications and devices that capitalize on their size, light-conversion efficiencies, emissive wavelengths, syntheses, and environmental stabilities. The two main topics of this dissertation are (i) the interrogation of laser power-dependent quantum yield and total radiant flux metrics for a homogeneous, solution phase upconversion nanocrystal composition under both continuous wave and femtosecond-pulsed excitation utilizing a custom engineered absolute measurement system, and (ii) the synthesis, characterization, and power-dependent x-ray excited scintillation properties of [Y2O3; Eu] nanocrystals, and their integration into a fiber-optic radiation sensing device capable of in vivo dosimetry.
Presented herein is the laser power-dependent total radiant flux and absolute quantum yield measurements of homogeneous, solution-phase [NaYF4; Yb (15%), Er (2%)] upconversion nanocrystals, and further compares the quantitative total radiant flux and absolute quantum yield measurements under both 970 nm continuous-wave and 976 nm pulsed Ti-Sapphire laser excitation (140 fs pulse-width, 80 MHz). This study demonstrates that at comparable excitation densities under continuous-wave and fs-pulsed excitation from 42 - 284 W/cm2, the absolute quantum yield, and the total radiant flux per unit volume, are within a factor of two when spectra are integrated over the 500 - 700 nm wavelength regime. This study further establishes the radiant flux as the true unit of merit for quantifying emissive output intensity of upconverting nanocrystals for application purposes, especially given the high uncertainty in solution phase upconversion nanocrystal quantum yield measurements due to their low absorption cross-section. Additionally, a commercially available bulk [NaYF4; Yb (20%), Er (3%)] upconversion sample was measured in the solid-state to provide a total radiant flux and absolute quantum yield standard. The measurements were accomplished utilizing a custom-engineered, multi-detector integrating sphere measurement system that can measure spectral sample emission in Watts on a flux-calibrated (W/nm) CCD-spectrometer, enabling the direct measurement of the total radiant flux without need for an absorbance or quantum yield value.
Also presented is the development and characterization of a scintillating nanocrystalline composition, [Y2-xO3; Eux, Liy], in which Eu and Li dopant ion concentrations were systematically varied in order to define the most emissive compositions under specific x-ray excitation conditions. It is shown that these optimized [Y2-xO3; Eux, Liy] compositions display scintillation responses that: (i) correlate linearly with incident radiation exposure at x-ray energies spanning from 40 - 220 kVp, and (ii) manifest no evidence of scintillation intensity saturation at the highest evaluated radiation exposures [up to 4 Roentgen per second]. X-ray excitation energies of 40, 120, and 220 kVp were chosen to probe the dependence of the integrated emission intensity upon x-ray exposure-rate in energy regimes where either the photoelectric or the Compton effect governs the scintillation mechanism on the most emissive [Y2-xO3; Eux, Liy] composition, [Y1.9O3; Eu0.1, Li0.16]. These experiments demonstrate for nanoscale [Y2-xO3; Eux], that for comparable radiation exposures, when scintillation is governed by the photoelectric effect (120 kVp excitation), greater integrated emission intensities are recorded relative to excitation energies where the Compton effect regulates scintillation (220 kVp excitation).
The nanoscale [Y1.9O3; Eu0.1, Li0.16] was further exploited as a detector material in a prototype fiber-optic radiation sensor. The scintillation intensity from a [Y1.9O3; Eu0.1, Li0.16]-modified optical fiber tip, recorded using a CCD-photodetector or a Si-photodiode, was correlated with radiation exposure using a Precision XRAD 225Cx small-animal image guided radiation therapy (IGRT) system, an orthovoltage cabinet-irradiator, and a clinical X-ray Computed Tomography (CT) machine. For all x-ray energies tested from 80 - 225 kVp, this near-radiotransparent device recorded scintillation intensities that tracked linearly with total radiation exposure, highlighting its capability to provide alternately accurate dosimetry measurements for both diagnostic imaging and radiation therapy treatment. Because Si-based CCD and photodiode detectors manifest maximal sensitivities over the emission range of nanoscale [Y1.9O3; Eu0.1, Li0.16], the timing speeds, sizes, and low power-consumption of these devices, coupled with the detection element's linear dependence of scintillation intensity with radiation dose, demonstrates the opportunity for next-generation radiation exposure measuring devices for in/ex vivo applications that are ultra-small, inexpensive, and accurate.
Item Open Access The development, characterization, and clinical investigation of a novel reusable radiochromic sheet for 2D dose measurement(2019) Collins, Cielle ElysePurpose: Radiochromic film remains a useful and versatile clinical dosimetry tool. While simple to use, current film options are single use, with no forms of reusable film available commercially. Here we introduce a novel 2D radiochromic sheet, derived from Presage material, which optically clears after irradiation and can be reused. We evaluate the sheets for potential as an economic alternative to radiochromic film and also as a radiochromic bolus with capability for dose measurement.
Methods: A novel derivative of reusable Presage® was manufactured into thin sheets of 5mm thickness. The sheets contained 2% cumin-leucomalachitegreen-diethylamine (LMG-DEA) and plasticizer (up to 25% by weight). A series of radiation experiments were performed to characterize the radiation response of the sheets irradiated with megavoltage radiation from a Varian medical accelerator over time and in different settings. The local change in optical-density (OD), before and after radiation, was obtained by scanning the sheets with a flat-bed film scanner and extracting the red channel of the RGB image. Repeat sheet scanning enabled investigation of the temporal decay of OD. Additional studies investigated dose sensitivity, consistency of response through repeat irradiations, intra and inter-sheet reproducibility, multi-modality response (electrons and photons), and temperature sensitivity (temperature range 22°C to 36°C) of the Presage® sheets. Clinical utility of the sheets was investigated through application to IMRT treatment plans (prostate and a TG119 commissioning plan), and a chest wall electron boost treatment. In the latter test, the sheet performed as a radiochromic bolus.
Results: The radiation induced OD change in the sheets was found to be proportional to dose and to decay to baseline after ~24 hours with a decay constant of 6.0 hours-1 (standard deviation 0.33). After this time the sheet could be reused and had similar sensitivity (within 1% after the first irradiation) for at least 8 irradiations. Importantly, the sheets were not observed to carry any memory of previous irradiations within measurement uncertainty. The consistency of dose response from photons (6MV and 15MV) and electrons (6-20MeV) was found to be within 1%. The dose sensitivity of the sheets was observed to have a temperature dependence of 0.0012 ΔOD/°C. For the IMRT QA verification test, good agreement was observed between the Presage sheet and EBT film (gamma pass rate of 97% at 3% 3mm and 99% at 5% 3mm dose-difference and distance-to-agreement tolerance, with a 10% threshold). For the TG-119 tests the gamma agreement was 93% pass rate at 5% 3mm, 10% threshold, when compared with Eclipse. For the electron cutout treatment, both Presage and EBT agreed well (within 2% RMS difference) but differed from the Eclipse treatment plan (~7% RMS difference) indicating some limitations to the Eclipse modeling in this case.
Conclusion: The reusable Presage sheets show promise as an economic alternative for film applications and as a radiochromic bolus for in-vivo dose measurement. The preliminary work presented in this thesis indicates that these sheets have the capability to improve care in the most well-equipped clinics in the world, as well as provide a fast, inexpensive, and easy to use dosimeter to clinics in low-income countries in desperate need of versatile resources. This work is still a preliminary study of feasibility, where the central current limitations include the narrow nature of application testing and lack of inter-batch comparison. Further work is recommended to establish use in a wide variety of clinical applications, establish a material more closely reflecting flexible bolus, and push the extent of the potential for reusability in the sheets.
Item Open Access Validation of Isodose Curves for AIRO Mobile CT, P-32 Pure-Beta and I-131 Mixed Beta/Gamma Detection Utilizing Nano-Fiber Optic Detector(2019) Smiley, Brianna RochelleProject 1: Validation of Isodose Curves for AIRO Mobile CT
Purpose: Validate isodose curves provided by the manufacturer for the Airo Mobile CT to determine if, indeed, it is safe for those who are operating the machine.
Materials and Methods: To determine the maximum number of scans per year allowed, hospitals rely on the data provided by the manufacturer. It is not common practice to verify the data provided for CT scanners. To validate the information provided by the manufacturer, the same CT settings were utilized for testing. The manufacturer settings were 120 kV, 100 mA and 1.92 sec and a 32 cm body CTDI phantom was used to generate scatter patterns. Replicating these conditions, two ion chambers were used to collect measurements of scattered radiation at different distances around the MobileCT gantry.
Results: Following the manufacturer settings, the average percent difference between the manufacturer data and the data collected in this experiment was 24.16 ± 15%.
Conclusions: The results provided information that confirmed the validity of the data provided by the manufacturer. Through this verification, it was shown that the scattered air kerma determined through experimentation was comparable to the data provided by the manufacturer.
Project 2: P-32 pure-beta detection utilizing nano-fiber optic detector
Purpose: Determine if the nano-fiber optic detector is capable of detecting pure β emissions by placing it in contact with P-32 in liquid solution.
Materials and Methods: The P-32 was placed into a vial with 2 mL of stabilizing solution. The vial was placed in a lead pig that was modified with a 1 mm opening on the lid for the nano-FOD to be inserted through. Measurements of the nano-FOD’s response to pure beta emissions were collected by submerging the nano-FOD into a vial containing 76.2 mCi of liquid P-32 and evaluating the voltage output that was produced. For P-32, this was done over a 45-day period to determine if the nano-FOD was able to accurately measure activity over time. From the data collected, the net signal and signal-to-noise ratio (SNR) were calculated and compared to the P-32 concentration, which showed a linear correlation when plotted.
Results: The nano-FOD was able to demonstrate a noticeable response when inserted into the P-32 solution. The data from the net signal allowed for the determination of the experimental half-life which was 13.46 ± 0.87 days. When compared to the published half-life of P-32, which is 14.29 days, the percent difference between the experimental and published half-life was 5.8%.
Conclusions: The results from this data collection provide confirmation that the nano-FOD device can be utilized as a real-time β detector. Using Monte Carlo simulations, the signals measured with the nano-FOD have been calibrated to radiation exposure, proving the nano-FODs ability to be utilized as a novel β detector.
Project 3: I-131 mixed-beta and gamma detection utilizing nano-fiber optic detector
Purpose: Determine if the nano-fiber optic detector is capable of accurately detecting mixed β and γ radiation by placing it in contact with I-131.
Materials and Methods: The I-131 was placed into a vial with 2 mL of stabilizing solution. The vial was placed in a lead pig that was modified with two openings on the lid for each of the nano-FODs to be inserted through. The first opening was used to insert directly into the I-131 solution to be exposed to both the β and γ emissions. The second opening led the nano-FOD into a Lucite sheath that blocks all β emissions, so that only the γ component was detected by the nano-FOD. Measurements of the nano-FOD’s response to mixed β and γ emissions were collected by submerging the nano-FOD into the vial containing 105 mCi of liquid I-131 and evaluating the voltage output that was produced. For I-131, this was done over a 20-day period to determine if the nano-FOD was able to measure activity over time for both the mixed signal and the gamma signal.
Results: The signal produced by the nano-FOD from being exposed to the mixed beta and gamma emissions of I-131 shows the nano-FODs capability of detecting radiation in mixed fields. The net signal over time provided an experimental half-life comparable to that of the published half-life of I-131.
Conclusions: The nano-FOD is capable of functioning in a mixed field. The post-processing data analysis for this nano-FOD needs modification and will provide insight into the future of utilizing the nano-FOD in mixed fields.
Item Open Access Validation of the dosimetry for a Lay-down Total Skin Irradiation techniques by Monte Carlo Simulation(2019) Li, RuiqiTotal skin irradiation (TSI) with electron beam has been very effective for patient with Mycosis fungoides. We recently developed and implemented a technique of laying down position for patients who are too frail for the standard standing position. In this study, we validated these measurements with Monte Carlo (MC) simulation which can provide more information on dose distributions and guidance on further optimization of the technique. The laydown technique consists of 6 equi-spaced beam directions relative to the patient cranial-caudal axis, similar to the standup technique. For the AP/PA directions (vertex fields), patient is placed directly under the gantry at 195cm source-to-skin distance (SSD) and 3 overlapping fields with gantry angles 60˚ apart are used. For the four oblique directions, patient is repositioned on the floor parallel to the gantry rotation axis at SSD of 305 cm with gantry at 300˚. A customized 0.25 mm Cu filter was placed in the linac interface mount to further broaden the beam. Each treatment fraction consists of 10 fields and 3 of them are unique. The Monte Carlo simulation was performed within the EGSnrc environment, using the phase space file provided by the linac vendor. The following quantities were studied and compared with the measurements: for each field/direction at the treatment SSDs, the percent depth dose (PDD), the profiles at the depth of maximum, and the absolute dosimetric output on the flat water phantom; the composite dose distribution on a cylindrical phantom of 30 cm diameter. Cu filter increases the beam FWHM by 44% but also reduces the output by 60%. The central regions within ±10% of the prescription dose were 170×70 cm2 for vertex fields and 140×80 cm2 for oblique fields. Profiles and output factors for both vertex fields and oblique fields agreed within 3% between MC and measurements. Vertex fields has dmax at (0.55: MC; 0.67: measurement)cm and R80 at (1.15; 1.40)cm, oblique field has dmax at (1.05; 0.86)cm and R80 at (1.55; 1.40)cm. When all fields are combined on the cylindrical phantom, the dmax shifted toward surface region. The composite dose distribution has the surface dose at (99.0; 95.2) %, dmax at (0.15; 0.15)cm, and R80 at (0.55; 0.75)cm. The maximum X-ray contamination at the central axis was (2.2; 2.1)%, and reduced to 0.2% at 40 cm off the central axis. Cylindrical phantom of 20 cm and 40 cm diameters for patient size simulation shows the surface dose of 93% and 103%, compared to 30 cm diameter. The Monte Carlo results in general agree well with the measurement, which provides secondary support in our commissioning procedure. In addition to those measurable quantities, the Monte Carlo simulation can provide further information such as the full dose distribution of the patient phantom, and the ability to investigate and optimize techniques such as different filter design, SSD and field size variations.