Browsing by Subject "Interventional Radiology"

Project 1 (Chapter 2): Dose Verification andMonte Carlo Modeling of an Image-GuidedSmall Animal Radiotherapy Irradiator

Purpose: Preclinical trials play a crucial role in advancing the understanding of cancer biology and developing effective therapeutic interventions. The purpose of this project is to simulate and validate beam output of a Small Animal Radiotherapy Research Platform (SARRP, xStrahl) with both physical dosimetry and Monte Carlo simulation models.

Materials and Methods: The SARRP console was set up to deliver an intended dose of 8Gy (4 Gy anterior-posteriorly (AP), 4 Gy posterior-anteriorly (PA)) in 142 seconds to a flat mouse phantom. The x-ray irradiation parameters were set to 13 mA, 220 kVp, with a 33.725 cm source to surface distance. Beam filtration included 0.8 mm Be (inherent) and 0.15 mm Cu (added), with collimation set to 40x30 mm. Dose verification was conducted through two methods: utilizing an energy-calibrated MOSFET dosimeter and employing Monte Carlo Simulations using Monte Carlo N- Particle Transport (MCNP). MOSFET Calibration encompassed four setups to ensure precision. The first two involved calibrating the MOSFET with an ion chamber in air at 0 degrees (Setup 1) and 180 degrees (Setup 2). The subsequent two setups calibrated the MOSFET positioned inside the phantom (Setups 3 and 4) with an ion chamber in air. After the calibrations, the MOSFET, placed inside the phantom, received the intended 4 Gy dose for verification. The MCNP simulation comprised two stages: a point source simulation and a simulation of the x-ray tube. For the point source, the SARRP geometry was replicated, with the x-ray tube modeled as a collimated point source. The x-ray tube simulation entailed modeling components of the xray tube. Validation methods included comparing energy spectra, Half Value Layer (HVL) testing, and film analysis of the anode heel effect.

Results: In the dose verification, Setup 1 exceeds the intended 4 Gy dose by 7.72%, while Setup 2 underdoses by 2.96%, resulting in a cumulative overdose of 2.38% for Setups 1 and 2. Setup 3 aligns with the intended 4 Gy dose, underdosing slightly by 0.14%, while Setup 4 underdoses by 2.31%. The cumulative dose for Setups 3 and 4 totals 7.90 Gy, indicating a 1.27% underdose. The two calibration techniques demonstrate a difference of 3.6%. Calibration in air is the preferred method due to the ionization chamber also being present in air. Point Source Simulation yielded doses of (4.27 ± 0.02) Gy (AP) and(3.77 ± 0.02) Gy (PA). X-ray Tube Simulation resulted in (3.95 ± 0.02) Gy (AP). Energy spectrum of the MCNP model showed good agreement with the manufacturer model in key spectral characteristics (peaks, mean energies). HVL comparison showed good agreement with only a 0.5% difference between simulated and experimental half value thicknesses. The anode-heel effect analysis was inconclusive.

Conclusions: The dose verification processes establish the SARRP’s efficacy in delivering the intended radiation dose. The integration of advanced measurement techniques set a benchmark for small animal dosimetry and ultimately strengthens the reliability of radiation doses in preclinical studies.

Project 2 (Chapter 3): Investigation of Occupational Radiation Exposure to InterventionalRadiologists from Use of Fluoroscopic Imaging

Purpose: The purpose of this project is to investigate radiation exposure among Interventional Radiology (IR) physicians using fluoroscopic imaging through experimental data collection and retrospective analysis, with objectives to understand Automatic Exposure Rate Control mechanisms, assess exposure rates to operators, and identify trends amongIR physicians.

Materials and Methods: Three interventional fluoroscopes were investigated: Philips AlluraClarity Xper FD 20/15, Philips Allura Xper FD20, and GE Discovery IGS 740. Two phantoms were employed to replicate patient and operator. The “patient” phantom was comprised of water-equivalent slabs (5cm thick, 30cm x 30cm). The “operator” phantom (Atom Dosimetry Labs Adult Male phantom) was placed beside the table and covered with a 0.25 mm lead apron. A Ludlum 9DP pressurized ion chamber was positioned at collar level of the operator phantom. Parameters varied included patient thickness (20cm-40cm), collimation, and fluoroscopy and acquisition modes. Exposure (mR) to “operator”were measured and normalized to number of x-ray pulses. Retrospective analysis used Radiation Dose Structured Report data for an 8-month period. Physician caseload, averageCumulative Air Kerma (CAK) by physician, and total CAK by physician were determined.

Results: Based on measured data, acquisition mode exhibits longer pulse widths (7.20x-31.3x) and higher tube current (1.48x-7.58x) compared to fluoroscopy for all units. Tube voltage increases with phantom thickness in both fluoroscopy and acquisition mode for all units. Increasing phantom size and collimated field size elevate the operator exposure rate for all C-arms. Larger field sizes contribute to higher exposure rates compared to small field sizes (4.91x-6.27x fluoroscopy, 5.51x-8.23x acquisition). Additionally, acquisition mode contributes to higher exposure rates (23.4x–107.1x) than fluoroscopy. Analysis of proceduraldata identified trends in case distribution and dose to patients across physicians.

Conclusions: Overall, patient size, collimation settings, and fluoroscopy vs. acquisition mode were identified as significant contributors to operator exposure rates. Outliers among IR physicians highlighted the need for targeted interventions to mitigate excessive radiation exposure.

AbstractProject 1: Measuring the Effects on Operator Dose of Changing Clinical Settings Purpose: This study was initiated as part of a multi-faceted investigation of occupational dose to Interventional Radiologists consequential to their role as operators of fluoroscopy equipment. This project aims to qualitatively evaluate general dose reduction techniques, including clinical protocol settings on different interventional fluoroscopes to determine the specific impact on operator dose at Duke University Hospital. Materials and Methods: For each unit, analogous baseline settings were selected with a general abdominal protocol. The patient table was set to a source-to-object distance (SOD) of 62.23 cm (24.5 in) and a patient phantom was placed in the beam as a scatter medium similar to a typical patient abdomen. An anthropomorphic “operator” phantom was draped with a lead apron and positioned to one side of the patient table with an ion chamber placed at collar level. The ion chamber was placed such that the center of the active volume was 38.1 cm (15 in) lateral to and 63.5 cm (25 in) inferior from the center of the flat-paneled detector. A series of scans was taken on each unit, with each one having a selected variable changed, and the exposure readings from the ion chamber were recorded for comparison. Results: The effects on operator exposure rate of personnel height, contour shield use, cine mode, magnification, low dose mode, and source-to-image distance (SID) were analyzed. Operator height was found to have a larger effect on exposure rate reduction with distance than anticipated. Use of the contour shield reduced the operator exposure rate by over 90% on each unit. Use of cine mode drastically increased the exposure rate to the operator, while magnification, low dose mode, and decreasing SID all resulted in lower exposure rates. Conclusions: Operators can utilize these results to contextualize the effects of their own dose reduction techniques. Knowledge and familiarity of the techniques which offer the best exposure rate reduction can guide radiation protection practices among staff and help to optimize occupational doses. Project 2: Developing a Conceptual Framework for Analyzing the Radiation Dose Structured Report Purpose: When investigating occupational dose to Interventional Radiologists, it is important to be able to accurately compare metrics related to dose from historical procedures. The Radiation Dose Structured Report (RDSR) provides characteristic data from historical procedures. With an appropriate framework for analyzing RDSR data, performance metrics between operators or units can be compared, and identified trends can be used to develop dose reduction techniques specific to the organization. Materials and Methods: RDSR data from five interventional fluoroscopy systems (K1 – K5) was extracted for a three-year period from July 2019 through August 2022, and multiple metrics of comparison were selected for analysis. To determine differences in machine output, air kerma rates of similar procedures were compared, as well as the overall machine utilization for each year. Differences in operator-selectable variable were compared through air kerma rate per procedure, fluoroscopy time per procedure (limited to central line procedures), and operator caseload makeup. Results: Machine comparison of air kerma rates showed a consistently higher median and variability on the Philips Allura systems compared to the other three units. The Philips AlluraClarity unit in suite K2 was noticeably under-utilized by Interventional Radiology staff due to it being the primary fluoroscope used by Neurosurgery staff who were outside the scope of this investigation. Operator air kerma rates were compared from August 2021 through August 2022 and largely showed similar median values and variability. Fluoroscopy time per procedure fit to lognormal distributions and compared through their distribution parameter μ showed a median value which dipped during the second year for most providers. One operater also had a consistently higher median time per procedure for all three years. Conclusions: The analysis described by this framework provides a means of utilizing RDSR data to compare performance of interventional procedures. Continual local analysis of these metrics can be used to guide operator training to ensure that occupational doses are optimized to be as low as reasonably achievable. This is an initial approach that can be expanded through investigation and further characterization of procedure data included in the RDSR.