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Abstract

The build-up dose in an area like skin is very difficult to determine due to contributions from electron contamination which cannot be accounted for by the ionization chamber. Precise measurements in the build-up region are important to prevent tumors and cervical lymph. The Treatment Planning Systems (TPS) lack dose accuracy in the stated region. This study focuses on utilizing EBT2 Gafchromic Dye films to determine dose in the build-up region from a 6 MV photon beam generated from a VARIAN linear accelerator. This technique was also used to measure the depth-dose profile for each irradiation setting. The measured skin doses were then compared against the predicted values from the TPSs. EBT2 films along a beam axis prove to generate good and continuous sensitometric curves (depending on the scanner resolution) and show better agreement over other irradiation settings when films are at the isocentre or perpendicular to the incoming beam. Good agreements (~3%) in the percentage depth dose, at depths greater than 2 cm, were shown between the TPS, EBT2 and ROOS chambers. At the tail of the curve where the dose is low, the percent dose difference analysis would show higher values (from 8 to 10%). Results also show that in order to obtain very precise measurements, care must be taken during the irradiation and scanning of EBT2 films. Reasons for disagreement between different dosimetric techniques and features of differing scanning systems for analyzing EBT2 films were discussed.