Research on photo neutron dose to patient by (n, p) reaction from a 15 MV linear accelerator

Abstract

Introduction: Photoneutron produced during radiotherapy treatment was measured and the possibility for the radiation yield by the (n, p) reaction within the body was calculated. Materials and Methods: Photoneutron spectrum was measured using Columbia Resin (CR 39) film from a Siemens Primus Plus Linear accelerator and the possibility for the radiation yield by the (n, p) reaction within the body was calculated during radiotherapy treatment. Results---The photoneutron spectrum was measured with CR 39 SSNTD and automatic track counting software. The interaction cross section for the (n,p) reaction for each energy and element were determined and radiation yield was calculated.For hydrogen, there is no (n,p) reaction. The (n,p) reaction is absent in C12for neutron of energy below 13.5 MeV. Oxygen has (n,p) reaction above 10 MeV. Nitrogen has a low threshold and there is no threshold for potassium and calcium. Conclusion---From the result, it is clear that (n, p) reactions are significant and even though the dose from these reactions is low, the impact will be severe due to the high LET nature of proton. The data can be used to minimize the photoneutron production during the radiotherapy treatment in the future. The outcome of the work indicates the importance of photoneutron transport and dose deposition to be included in the treatment planning algorithm.