Room: AAPM ePoster Library
Purpose: Classical techniques require two gantry angles to compose a total skin electron therapy (TSET) treatment. Our goal is to reduce the treatment time by using one gantry angle. Monte Carlo (MC) simulations were used to design an electron compensator mounted in the accessory slot in a linac to generate a homogeneous dose distribution.
Methods: A previously-validated MC model of an electron accelerator was further validated for long source-to-surface distances (SSD) using profile measurements. The gantry angle and the collimating jaws were set to 90° and 40x40cm², respectively. The secondary scattering foil was removed to reduce bremsstrahlung production. A phantom was modeled at 300cm SSD to mimic a patient treatment. The electron compensator was mounted in the accessory slot, and was composed of several layers of aluminum foils with different dimensions. The treatment head was simulated with 9 MeV electrons and profiles and depth dose curves were calculated in water. The thickness of each aluminum foil and the step size was modified until an optimal dose distribution was achieved.
Results: The profiles measured to validate the MC model are within 3% of calculations for most of the points. Using the aluminum compensator resulted in a homogeneous dose distribution across the lateral profile, with a maximum 10% dose variation along 120cm vertical direction. Using the compensator, the depth dose curve shifted ~0.5cm towards the surface. The bremsstrahlung background was on the order of ~1.2%. The removal of the secondary scattering foil reduced the bremsstrahlung background by ~0.2%.
Conclusion: Monte Carlo simulations were used to study and design a compensator that could be placed in the accessory slot to obtain a homogeneous dose distribution for TSET. The preliminary results with the aluminum compensator revealed an ideal dose distribution and a method to reduce the treatment time.