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Assessment of the Point-Source Method for Estimating Dose Rates to Members of the Public from Exposure to Patients with 131I Thyroid Treatment

Dewji, Shaheen Azim*; Bellamy, Michael*; Hertel, Nolan*†; Leggett, Richard*; Sherbini, Sami; Saba, Mohammad; Eckerman, Keith*


There is an error in the paper by Dewji et al. entitled, “Assessment of the Point-source Method for Estimating Dose Rates to Members of the Public from Exposure to Patients with 131 I Thyroid Treatment,” which appeared in the September 2015 issue. The last sentence in the third paragraph under “Results” on p. 239 should be removed, and the paragraph should read as follows:

“The point-source derived dose rate values were calculated using the method outlined in National Council on Radiation Protection and Measurements (NCRP) Report No. 37 (National Council on Radiation Protection and Measurements 1970). The ratios of the dose rates based on the point source to values derived using PIMAL are summarized in Table 2, where the PIMAL values account for time-dependent biokinetic movement of systemic iodine. As summarized in Table 2, the point-source method grossly overestimates the external dose rate to the exposed person at the 10 cm separation distance, regardless of initial exposure time or uptake mode.”

Health Physics. 110(3):307, March 2016.

doi: 10.1097/HP.0000000000000327

The U.S. Nuclear Regulatory Commission (USNRC) initiated a contract with Oak Ridge National Laboratory (ORNL) to calculate radiation dose rates to members of the public that may result from exposure to patients recently administered iodine-131 (131I) as part of medical therapy. The main purpose was to compare dose rate estimates based on a point source and target with values derived from more realistic simulations of a human source and target. The latter simulations considered the time-dependent distribution of 131I in the patient and attenuation of emitted photons by the patient’s tissues. The external dose rate estimates were derived using Monte Carlo methods and two representations of the Phantom with Movable Arms and Legs (PIMAL), previously developed by ORNL and the USNRC, to model the patient and a nearby member of the public. Dose rates to tissues and effective dose rates were calculated for distances ranging from 10 cm to 300 cm between the phantoms. Dose rates estimated from these simulations are compared to estimates based on the point-source method, as well as to results of previous studies that estimated exposure from 131I patients. The point-source method overestimates dose rates to members of the public in very close proximity to an 131I patient but is a broadly accurate method of dose rate estimation at separation distances of 300 cm or more at times closer to administration.

*Oak Ridge National Laboratory, 1 Bethel Valley Road, MS-6335, Oak Ridge, TN 37831, USA; †Georgia Institute of Technology, 770 State Street, Atlanta, GA 30332–0745, USA; ‡United States Nuclear Regulatory Commission, Washington, DC 20555–0001.

Corresponding Author: S. Dewji, Oak Ridge National Laboratory, 1 Bethel Valley Road, MS-6335, Oak Ridge, TN 37831, USA; Tel: (865) 576–9348; Fax: (865) 574–8912; E-mail:

The authors declare no conflicts of interest.


This work was funded by the United States Nuclear Regulatory Commission under contract number NRC-HQ-60-11-D-0024 with Oak Ridge National Laboratory.

Notice of Copyright

This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (

(Manuscript accepted 1 May 2015)

© 2015 by the Health Physics Society