On effective dose for radiotherapy based on doses to nontarget organs and tissues

Purpose: The National Council for Radiation Protection and Measurement (NCRP) published estimates for the collective population dose and the mean effective dose to the population of the United States from medical imaging procedures for 1980/1982 and for 2006. The earlier report ignored the effective dose from radiotherapy and the latter gave a cursory discussion of the topic but again did not include it in the population exposure for various reasons. This paper explains the methodology used to calculate the effective dose in due to radiotherapy procedures in the latter NCRP report and revises the values based on more detailed modeling. Methods: This study calculated the dose to nontarget organs from radiotherapy for reference populations using CT images and published peripheral dose data. Results: Using International Commission on Radiological Protection (ICRP) 60 weighting factors, the total effective dose to nontarget organs in radiotherapy patients is estimated as 298 +/- 194 mSv per patient, while the U. S. population effective dose is 0.939 +/- 0.610 mSv per person, with a collective dose of 283 000 +/- 184 000 person Sv per year. Using ICRP 103 weighting factors, the effective dose is 281 +/- 183 mSv per patient, 0.887 +/- 0.577 mSv per person in the U. S., and 268 000 +/- 174 000 person Sv per year. The uncertainty in the calculations is largely governed by variations in patient size, which was accounted for by considering a range of patient sizes and taking the average treatment site to nontarget organ distance. Conclusions: The methods used to estimate the effective doses from radiotherapy used in NCRP Report No. 160 have been explained and the values updated. (C) 2015 American Association of Physicists in Medicine.