energy optimization and calculation of dose absorption enhancement factor in photon activation therapy

introduction: secondary radiation such as photoelectrons, auger electrons and characteristic radiations cause a local boost in dose for a tumor when irradiated with an external x-ray beam after being loaded with elements capable of activating the tumor, e.g.; i and gd. materials and methods:  in this investigation, the mcnpx code was used for simulation and calculation of dose enhancement factor for a tumor loaded with activating elements. the designed model comprised the x-ray source, phantom (target tissue and loaded tumor with activating agent), detector, interactions modeling and results. the source was defined as monochromatic and plane surface situated at 50 cm (z = 50). phantom geometry was a 10 × 10 × 10 cm3 cube centered at (0, 0, 0) with a 2.2 × 2.2 × 2.2 cm3 cubic tumor with a center located at 3 cm depth inside the phantom results: dose enhancement factor and optimum energy in radiotherapy are evaluated using the photon activation therapy method. result show that the dose enhancement factor increases with activating concentration in the tumor. the maximum dose enhancement factor for iodine in the tumor occurs for photons in the energy range of 50-60 kev. dose uniformity is less for lower energy photons within the activated region inside the tumor. results indicate that the dose enhancement factor varies linearly with the activating concentration agent. discussion and conclusion: in this study, the obtained results point out a considerable enhancement in dose in the presence of activating agents in the tumor regions.