investigation of neutron dose and secondary cancer risk in pelvic and brain radiotherapy with a high-energy linac

‎this work aimed to assess the secondary cancer risk for patients undergoing brain and pelvic radiotherapy with high-energy linear accelerators (linac)‎. ‎photoneutrons are produced in the linac’s head when operating above 7 mev and are not considered in radiotherapy treatment planning‎. ‎the mcnpx2.6 monte carlo code was used for linac’s head simulation‎. ‎the photon and neutron doses were calculated in tissues/organs of an international commission on radiological protection (icrp) male reference voxel phantom undergoing pelvic and brain radiotherapy‎. the results indicated that the neutron equivalent dose was higher for tissues/organs located close to skin and‎, ‎contrary to the photon equivalent dose‎, ‎did not decrease sharply for tissues/organs outside of the irradiation field‎. ‎notably‎, ‎neutron equivalent dose distribution was almost homogenous in whole body and did not depend on the treatment type and location of target organ‎. ‎therefore‎, ‎an undesirable dose was received by healthy tissues/organs‎, ‎leading to an increase in secondary cancer risk‎. ‎based on the obtained results‎, ‎the neutron effective dose for the pelvic and brain treatment were 0.20 and 0.26 msv.gy-1‎, ‎respectively‎. ‎the results also indicated that maximum secondary cancer risk due to neutrons was for colon (0.026 %) in the pelvic treatment‎, ‎while in brain treatment‎, ‎it belongs to stomach (0.036 %) for a delivered dose of 70 gy‎. ‎it is recommended that a mean neutron effective dose value of 0.23 msv.gy-1 can be considered in brain and pelvic treatment planning for evaluating the secondary cancer risk of high-energy linac radiotherapy‎.