Investigation of depth dose distribution from electron beam at shallow depth by means of Gafchromic EBT3 polymer films and ionization chamber

Abstract

Introduction Radiochromic film Gafchromic EBT3 can be used in the geometry when it is parallel to the beam axis allowing obtain absorbed dose depth distribution in a phantom during “single shot” of an accelerator. This method is useful for characterization of the electron beams of intraoperative accelerators because for this modality one needs a precise knowledge of the dose depth distribution starting from the phantom surface. Purpose The purpose of this work is to compare experimentally and in simulation depth dose curves obtained using Gafchromic EBT3 film and ionization chamber. Materials and methods The experimental comparison of the depth dose curves was carried out using 6 and 9 MeV electron beams of Elekta Synergy accelerator and 6 MeV electron beam of intraoperative therapy betatron. The dose distributions were measured by ionization chambers and by Gafchromic EBT3 films in different phantoms. The Monte-Carlo simulation of the process was carried out using PCLab software developed at Tomsk Polytechnic University that allows simulation of the beam interaction with the matter. Results Experimental results show that percentage depth dose measured by the film at the shallow depths is less than the one measured by ionization chamber. Simulation results show the same difference. The simulation also shows that depth dose distribution “measured” by the film is close to the one in the pure water. Conclusion Results show that depth dose distribution from electron beam in water measured by radiochromic film is more precise at shallow depths than the one measured by ionization chamber.