S2022
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Material/Methods:
The patient was diagnosed with subcutaneous panniculitis-like T-cell lymphoma, and the subcutaneous target was prescribed to 2000 cGy in 10 fractions, every other day. Simulation and treatment were performed in two patient orientations, namely head-first supine and feet-first supine. A rotating table overlay was used to transition between the two orientations. We used the VMAT technique on a Varian TrueBeam linear accelerator. 5 isocenters were needed (3 for the head-first supine, and 2 for the feet- first supine), with >2 cm overlap between beams of adjacent isocenters. No physical bolus was placed for treatment. To improve robustness near the skin surface, a virtual bolus was used for optimization and then removed for final dose calculation. A dry run was performed prior to treatments. On Fractions 1 and 8, thermoluminescent dosimeters (TLD) measurements with 3 mm bolus were acquired at 17 and 6 different sites, respectively. Results:
QA of the treatment plan showed gamma compliance at more than 95%. The duration of one fraction did not exceed 75min. Conclusion: The proposed treatment for simultaneous TBI and TSI is technically demanding but feasible using the VMAT technique. It can be assumed that the use of a thicker layer of neoprene would improve this result. The use of fluence widening protects the patient from possible set-up variations. A large advantage of this technique is the possibility of obtaining a dose distribution at an acceptable level, which is safe for the patient in terms of dosimetry, in a relatively short treatment time. Keywords: simultaneous, TBI, TSI Feasibility Assessment of the Planning and Treatment of Total Subcutaneous Irradiation (TSQI) Tze Yee Lim 1 , Bouthaina Dabaja 2 , Dershan Luo 1 , Sara Thrower 1 , Dong Joo Rhee 1 , Tucker Netherton 1 , He Wang 1 , Xin Wang 1 1 Department of Radiation Physics, University of Texas MD Anderson Cancer Center, Houston, USA. 2 Department of Radiation Oncology, University of Texas MD Anderson Cancer Center, Houston, USA Digital Poster Highlight 5051 Purpose/Objective: We investigated the feasibility of the planning and treatment of Total Subcutaneous Irradiation (TSQI), whereby the subcutaneous layer throughout the body is irradiated. This target, being of annular shape (in axial view) and close to skin, is challenging to plan, set up, and treat.
The patient was able to tolerate the lengthy treatments (107±34 mins/fraction). On Fraction 1, the average TLD measurement was 108.3±6.0% of prescription dose. Full dose was able to be achieved on the skin without the use of a physical bolus, which would have been difficult to encompass the whole body with no air gaps. By Fraction 8, there was a noticeable discrepancy in patient separation at the abdomen based on cone-beam CT imaging. This was due to patient weight loss, primarily in the abdominal region. The patient separation in other areas of the body remains largely unaffected. The TLD measurements on Fraction 8 indicated 119.9±8.4% of the prescription dose at the abdomen. A verification
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