A passive method for absolute dose evaluation ofphotoneutrons in radiotherapy

Background: photoneutrons are produced during the radiotherapytreatment, when high energy x rays interacts with structures of the head ofthe linear accelerator (linac). the present day tps are not taking into accountthe photo-neutron dose and the biological effects associated with it. the lateinduction of cancer and recurrence of the disease in old cancer patients arebeing frequently reported. materials and methods: patients undergoingradiotherapy treatment with 15 mv x rays from a siemens primus plus linearaccelerator was considered for the study. in the present work, photoneutronspectrum from the linac head is measured using cr 39 ssntd and thecorresponding dose is calculated using geant4. the composite photoneutronspectrum from the linac head and the corresponding dose was calculatedusing the kerma evaluation method in a human equivalent tissue phantom.the repeated calculation outcomes and the covariance error analysis in thenuclear data give consistency and an accuracy of 2 % in the results. results:the result shows that significant amount of photoneutron dose wasdeposited during radiotherapy treatment when high energy x rays are used.the photoneutron production from the patient itself is yet another majorissue which will cause out off field dose. conclusion: this work givesimportance in considering the photoneutron dose during radiotherapyplanning and protection. this extra dose might be a factor that contributes tothe induction of cancer and also to the recurrence of cancer to previouslycured patients.