An estimate of the radiation-induced cancer risk from the whole-body stray radiation exposure in neutron radiotherapy

Abstract

The 1980 BEIR III risk factors have been used to estimate the secondary cancer risks from the whole-body stray radiation exposures which occur in neutron radiotherapy. The cancer risks have been calculated using the linear, linear-quadratic and quadratic dose-response models for the gamma component of the stray radiation. The linear dose-response model has been used to calculate the risk for the neutron component of the stray radiation. These risk estimates take into consideration for the first time the age and sex distribution of cancer patients undergoing neutron therapy. Changes in the cancer risk as a function of the RBE (10–100) assigned to the stray neutron radiation component have also been assessed. The excess risks in neutron-treated patients have been compared to the excess cancer risks for photon-treated patients and with the expected incidence of cancer in a normal population having the same age and sex distribution. These risk estimates clearly indicate that it will be necessary to tolerate a higher incidence of secondary cancers in patients undergoing fast neutron therapy than is the case with conventional photon therapy. However, for neutron RBEs of less than 50 the increased cancer risk is only a fraction of the normal expected incidence of cancer in this population. Moreover, comparison of the radiation-induced cancer risk with reported normal tissue complication rates in the treatment volume indicates that the excess cancer risk is substantially lower than the risk from other late normal tissue effects.