Browsing by Subject "Total body irradiation"
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Item Open Access Evaluation of the Total Body Irradiation Treatment Planning Using Eclipse(2019) Zeng, QiPurpose: Total Body Irradiation (TBI) is typically performed at extended source-to-skin distance (SSD), and the treatment planning is done by simple point dose calculation based on measurement data. The goal of this study is to validate the use of a computerized treatment planning system (TPS, Eclipse) in TBI planning. Typical TPS is commissioned with beam data collected at standard SSD of 100 cm. Extrapolation is required when planning treatments at extended SSDs beyond 400 cm. This requires comprehensive validation.
Methods: Rectangular water phantoms of different sizes were created in Eclipse. Various dosimetric factors including absolute output at extended SAD, phantom scatter factors, off-axis ratios, TMRs, spoiler factors, and compensator transmission factors were calculated in Eclipse using Analytical Anisotropic Algorithm (AAA, V10) and compared with the TBI commissioning measurements at the same geometry. Homogeneous patient phantoms approximating patient body sizes were created with MATLAB and imported into Eclipse. Dose distributions were calculated in Eclipse, and representative point doses were compared with measurements obtained during treatment and those from standard manual calculation.
Results: Dosimetric factors calculated in Eclipse showed good agreement with TBI commissioning measurements. The differences were all within 2% in the range of clinical situations, with most of them within 1%. When comparing in vivo dose measurements and Eclipse calculations, umbilicus (central axis) dose showed better agreement than the lung. Along the midline, doses at head and umbilicus agreed better with prescribed dose than doses at neck, lung, and lower legs.
Conclusion: This work demonstrates that Eclipse can be used for TBI planning at extended SSD with beam data from standard SSD. The Eclipse provides not only dose at certain points, but also full 3D dose distributions that allow more detailed evaluation of the patient treatment plan, hence reducing the need for time-consuming in vivo dose measurements.
Item Open Access Harnessing T Cell Generation and Metabolism to Modulate T Cell Recovery Following Radiation Exposure and Bone Marrow Transplantation(2022) Zou, YujingTotal body irradiation (TBI) causes profound suppression of hematopoiesis and T cell depletion, increasing chances of morbidity associated with opportunistic infections in the lymphopenic condition. Currently, therapeutic options for improving recovery of the T cell compartment following radiation exposure are not available. Although mouse and nonhuman primate studies have demonstrated prolonged effects of TBI on T cell reconstitution, there is a lack of understanding in the kinetics and metabolic signatures of radioresistant T cells actively undergoing homeostatic proliferation. Furthermore, whether kinetics of systemic T cell recovery recapitulates T cell recovery in circulation remains unknown. In the current study, we performed comprehensive immunophenotyping and single-cell sequencing analyses of radioresistant T cells, as well as imaging of T cell recovery in vivo, to determine preferentially upregulated pathways during T cell recovery. We identified T cell populations unique to TBI treatment that upregulate components essential to support oxidative phosphorylation, a mitochondria-dependent metabolic process. We further investigated mechanisms of recovery in donor T cells following TBI exposure in the bone marrow transplant setting. We demonstrated that recovery of alloreactive donor T cells was highly dependent on aerobic glycolysis, which can be manipulated to reduce graft-versus-host-disease and preserve the functional recovery of non-alloreactive donor T cells. We then examined the effect of NT-I7, a long-acting recombinant human IL-7, in mediating T cell reconstitution due to its role in integrating metabolic requirements with pathways critical for T cell survival and growth. We found that NT-I7 led to accelerated T cell recovery following TBI through both thymic-dependent and independent pathways. More importantly, NT-I7 promoted functional T cell recovery. Taken together, these findings reveal unique kinetics and mechanisms of T cell recovery in response to radiation. The study also identified NT-I7 as a potential therapeutic treatment during T cell lymphopenia by supporting critical mechanisms utilized in T cell recovery.
Item Open Access Investigation of AP/PA Recumbent Technique for Total Body Irradiation(2020) Liang, XiaominPurpose: Total body irradiation (TBI) is to deplete patient’s bone marrow and suppress the immune system by delivering uniform dose to patient’s whole body with a relatively low dose rate. The widely used total body irradiation (TBI) protocol in many institutions is to extend the source to surface distance (SSD) to over 400 cm in a large treatment room. The TBI techniques currently used at Duke University Medical Center is anteroposterior (AP)/posteroanterior (PA) technique and bilateral technique. Though bilateral technique TBI is executed with simpler treatment planning and setups in a more comfortable position, it could not provide adequate shielding to lungs and kidneys using blocks like AP/PA TBI technique. However, the whole process of block fabricating and verification is labor-consuming and time-costing. This project aims to develop a better AP/PA TBI treatment method in recumbent position, which provides better sparing for lungs and kidneys in any treatment room.
Methods: In this study, we considered different treatment techniques (three-dimensional conformal radiation therapy (3DCRT) and intensity-modulated radiation therapy (IMRT)), different treatment position (on the floor or on the couch), and different setups (gantry rotation and platform movement). TBI treatment plans were simulated in Eclipse treatment planning system by using both water equivalent phantom and patient CT image. Prescription for the treatment plans was 200 cGy per fraction with 4 fractions. The dose homogeneity should within ±10% of the prescription dose. Dose constraints for kidney and lung are 25% of the prescription dose. In 3DCRT TBI, we applied multi-leaf collimators (MLCs) for OARs shielding and used boost field to provide adequate dose to lungs and kidneys. For IMRT TBI, an iterative optimization algorithm was generated for increasing dose uniformity. By using IMRT, dynamic multi-leaf collimators (DMLCs) provided shielding for kidneys and lungs, which were considered in fluence map optimization. Volume dose and dose profiles were used to analyze the dose uniformity. Measurements with solid water phantom in treatment room were performed to verify the simulation results. IMRT QA with portal imager was performed for phantom.
Results: 3DCRT could not ensure the dose homogeneity and dose deliver accuracy at the same time. To ensure the dose homogeneity in 3DCRT TBI, patient/platform position should be changed between field or applying customized wedge to compensate the inverse square law. For IMRT, the optimization algorithm has excellent performance for both phantom and patients. The dose homogeneity in the mid-plane of both phantom and patients were less than ±5% of the prescription dose after a few iterations. Lungs and kidneys could receive around 25% prescription dose. The simulation and measurement results agree with each other. No additional physical compensators or partial transmission blocks were needed. Portal dose and predict dose perfectly agreed with each other. CR film worked well in positioning. Surface dose enhancement under blocked field was observed.
Conclusion: IMRT technique performed much better than 3DCRT in TBI treatment. In this study, we develop an AP/PA recumbent position IMRT TBI technique that could be used in any linac room. This technique can ensure high dose homogeneity, provide better sparing to lungs and kidneys, and reduce the complexity of TBI treatment planning without the need of labor-intensive compensators and partial transmission blocks.
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.