title: The risk of second primary cancers due to peripheral photon and neutron doses received during prostate cancer external beam radiation therapy.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: 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: Eva.Bezak@unisa.edu.au.
authors.forename: Eva
authors.initials: E
authors.lastname: Bezak
authors.affiliation: School of Physical Sciences, University of Adelaide, Adelaide, Australia; The Thailand Office for Peace, Bangkok, Thailand.
authors.forename: Rundgham
authors.initials: R
authors.lastname: Takam
authors.affiliation: Department of Radiation Oncology, Royal Adelaide Hospital, Adelaide, Australia; School of Medicine, University of Adelaide, Adelaide, Australia.
authors.forename: Eric
authors.initials: E
authors.lastname: Yeoh
authors.affiliation: School of Physical Sciences, University of Adelaide, Adelaide, Australia; Faculty of Science, University of Oradea, Oradea 410087, Romania.
authors.forename: Loredana G
authors.initials: LG
authors.lastname: Marcu
mesh_terms: D006801:Humans; D008297:Male; D009381:Neoplasms, Radiation-Induced / Q000453:epidemiology*; D016609:Neoplasms, Second Primary / Q000453:epidemiology* / Q000209:etiology; D009502:Neutrons / Q000009:adverse effects* / Q000627:therapeutic use; D058958:Organs at Risk; D017785:Photons / Q000009:adverse effects* / Q000627:therapeutic use; D011471:Prostatic Neoplasms / Q000453:epidemiology / Q000532:radiotherapy*; D020266:Radiotherapy, Conformal / Q000009:adverse effects*; D018570:Risk Assessment
keywords: Competitive risk model; Peripheral dose; Risk assessment; Second primary cancer