Room: Exhibit Hall | Forum 9
Purpose: The standard total skin irradiation (TSI) procedure at our clinic is based on the Stanford technique with patients standing and rotating in 6 positions at extended SSD. It works well except when patients are too frail to safely stand for a prolonged time. We recently developed and implemented a technique for these patients in a laying down position.
Methods: A poly-carbonate platform with recessed side wheels was constructed to place patient as close to the floor as possible. A customized Cu scattering filter was constructed and placed in interface mount to broaden the beam. For AP/PA position, the platform is placed under the linac and three overlapping subfields with gantry angles 60Ëš apart are used. For the oblique fields, the platform is wheeled out and rotated 90Ëš at 305 cm SSD and gantry at 300Ëš. EBT3 films were sandwiched in cylindrical phantoms to measure the PDDs. Additionally, OSLDs were placed on the Rando phantom to verify dose distributions.
Results: Imaging show excellent uniformity of the Cu filter which increases the dose profile FWHM by 42%. Optimal beam weighting of 1.0:0.22:1.0 was found for the subfields of AP/PA position to produce the most flat profile at dmax. The composite PDD from all six directions on the cylindrical phantom shows that the dmax at 0.15 cm, surface dose at 95% and R50 at 1.5 cm. The X-ray contaminant is 2.2%. OSLD results are comparable with the standing technique. In-vivo dose measurements from the first 2 patients agree with the expectations. Treatment time is ~22 minutes excluding initial preparations.
Conclusion: We have commissioned and implemented clinically an efficient floor-based TSI technique for frail patients. Extensive dosimetric measurements have been performed to derive planning parameters and to verify the dose distributions. This is a viable alternative to the standing up technique.
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