Out-of-field organs can be affected by secondary radiations originating from high energy linear accelerators, leading to an increased risk of carcinogenesis. The aim of this work was to determine the risk of second primary cancers (SPC) in the organs distal to the prostate during 3D conformal radiotherapy.
Based on previously measured peripheral photon and neutron doses in a Rando phantom using an 18MV photon beam, SPC risks in the out-of-field organs were estimated using the linear-no-threshold and the competitive risk models. Whole body as well as organ specific risk coefficients were used to calculate the SPC risks in order to estimate upper and lower risk limits, given the uncertainties associated with the coefficients.
The corresponding estimated average SPC risks ranged from 1.5±0.3% for thyroid to 4.5±4.2% for colon using whole body risk coefficients and 0.12±0.03% and 1.45±1.34%, respectively, using organ specific risk coefficients. The linear-no-threshold and the competitive risk models resulted in the same risk estimates (within the estimated errors) in the dose range received by out-of-field organs (≤1Gy). Distally located organs such as lungs, oesophagus, and thyroid received higher neutron versus photon dose.
The findings have important radiation protection implications when using high energy linear accelerators, as radiation protective measures could be employed to minimize the secondary out-of-field radiation for patients undergoing high energy external beam irradiation of the prostate.
Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB). 2017 Mar 13 [Epub]
Eva Bezak, Rundgham Takam, Eric Yeoh, Loredana G Marcu
School of Health Sciences, University of South Australia, Adelaide, Australia; Sansom Institute for Health Research, University of South Australia, Adelaide, Australia; School of Physical Sciences, University of Adelaide, Adelaide, Australia. Electronic address: ., School of Physical Sciences, University of Adelaide, Adelaide, Australia; The Thailand Office for Peace, Bangkok, Thailand., Department of Radiation Oncology, Royal Adelaide Hospital, Adelaide, Australia; School of Medicine, University of Adelaide, Adelaide, Australia., School of Physical Sciences, University of Adelaide, Adelaide, Australia; Faculty of Science, University of Oradea, Oradea 410087, Romania.