AbstractID: 8228 Title: Verification of Dose in Region above D_max for Clinical Photon Beams Using an Extrapolation and a Parallel Plate Chamber, Compared with Monte Carlo Simulation
Accurate quantification of dose distribution of high energy photons in the build-up region is essential to avoid under dosage or over dosage of subcutaneous skin and superficial tissues. Due to the existence of high dose gradient and charge particle non-equilibrium in the region before maximum depth dose, it is preferable to measure the percentage depth dose values using a parallel plate or an extrapolation chamber. In this study, the characteristics of dose in the region above dose max for high-energy photon beams is extensively studied. Beam, a general purpose
Monte Carlo code is used to model and simulate the Linac. The generated phase space files of transported particles were used to calculate the dose distribution in a phantom of voxel size 0.2cm
3
. The present study indicates that data measured with extrapolation and parallel plate chamber agrees favorably with the Monte Carlo data, both of which indicating that the surface dose is significantly higher at the skin and a few mm beneath, as compared to the conventionally accepted percentages. The maximum percentage difference was 6% at 0.5mm close to the surface of the phantom while other data points were within 3%.