title: Radiation dose and contralateral breast cancer risk associated with megavoltage cone-beam computed tomographic image verification in breast radiation therapy.
abstract: OBJECTIVE
  To measure and compare organ doses from a standard tangential breast radiation therapy treatment (50 Gy delivered in 25 fractions) and a megavoltage cone-beam computed tomography (MV-CBCT), taken for weekly image verification, and assess the risk of radiation-induced contralateral breast cancer.
  
  
  METHODS
  Organ doses were measured with thermoluminescent dosimeters placed strategically within a female anthropomorphic phantom. The risk of radiation-induced secondary cancer of the contralateral breast was estimated from these values using excess absolute risk and excess relative risk models.
  
  
  RESULTS
  The effective dose from a MV-CBCT (8-monitor units) was 35.9 ± 0.2 mSv. Weekly MV-CBCT imaging verification contributes 0.5% and 17% to the total ipsilateral and contralateral breast dose, respectively. For a woman irradiated at age 50 years, the 10-year postirradiation excess relative risk was estimated to be 0.8 and 0.9 for treatment alone and treatment plus weekly MV-CBCT imaging, respectively. The 10-year postirradiation excess absolute risk was estimated to be 4.7 and 5.6 per 10,000 women-years.
  
  
  CONCLUSIONS
  The increased dose and consequent radiation-induced second cancer risk as calculated by this study introduced by the imaging verification protocols utilizing MV-CBCT in breast radiation therapy must be weighed against the benefits of more accurate treatment. As additional image verification becomes more common, it is important that data be collected in regard to long-term malignancy risk.
authors.affiliation: Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia; Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia. Electronic address: aq908@uowmail.edu.au.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Quinn
authors.affiliation: Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia; Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia; School of Physics, University of Sydney, Sydney, NSW, Australia.
authors.forename: Lois
authors.initials: L
authors.lastname: Holloway
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia; Faculty of Medicine, University of New South Wales, Sydney, NSW, Australia; Collaboration for Cancer Outcomes Research and Evaluation, Liverpool Hospital, Liverpool, NSW, Australia.
authors.forename: Eng-Siew
authors.initials: ES
authors.lastname: Koh
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia; Faculty of Medicine, University of New South Wales, Sydney, NSW, Australia; Collaboration for Cancer Outcomes Research and Evaluation, Liverpool Hospital, Liverpool, NSW, Australia; School of Medicine, University of Western Sydney, Sydney, NSW, Australia.
authors.forename: Geoff
authors.initials: G
authors.lastname: Delaney
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia.
authors.forename: Sankar
authors.initials: S
authors.lastname: Arumugam
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia.
authors.forename: Gary
authors.initials: G
authors.lastname: Goozee
authors.affiliation: Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia; Liverpool and Macarthur Cancer Therapy Centres, NSW, Australia.
authors.forename: Peter
authors.initials: P
authors.lastname: Metcalfe