Abstract:
High energy x-rays from medical linear accelerators are contaminated by photoneutrons (threshold > 10 MV) due to interactions in the treatment machine head. The neutron dose equivalent received by patients from these fields has been documented in the literature; however this dose is not included as a part of normal treatment planning evaluation.Thus, the goal of this research is to attenuate the neutron flux from a medical linear accelerator and thus reduce the neutron dose equivalent at the patient plane. As the energy spectrum of photo neutrons from a medical linear accelerator resembles fission spectrum, significant attenuation will require the inclusion of a low atomic number moderator combined with a material having a high thermal neutron capture cross section.This research will investigate a moderator-absorber combination consisting of a solid mixture of paraffin wax and boron carbide positioned in the x-ray beam path. The neutron dose equivalent will be measured using indium and gold foil activation. The photon attenuation from this moderator-absorber will also be measured, as a loss in photon dose results in a longer beam-on time, and thus a higher initial neutron dose equivalent. The results will be compared to determine if the moderator-absorber is a feasible application for radiation oncology centers.