Title: Estimated dose rates to members of the public from external exposure to patients with ¹³¹I thyroid treatment

Abstract

The purpose of this study is to estimate dose rates that may result from exposure to patients who had been administered iodine-131 (¹³¹I) as part of medical therapy were calculated. These effective dose rate estimates were compared with simplified assumptions under United States Nuclear Regulatory Commission Regulatory Guide 8.39, which does not consider body tissue attenuation nor time-dependent redistribution and excretion of the administered ¹³¹I. Methods: Dose rates were estimated for members of the public potentially exposed to external irradiation from patients recently treated with ¹³¹I. Tissue attenuation and iodine biokinetics were considered in the patient in a larger comprehensive effort to improve external dose rate estimates. The external dose rate estimates are based on Monte Carlo simulations using the Phantom with Movable Arms and Legs (PIMAL), previously developed by Oak Ridge National Laboratory and the United States Nuclear Regulatory Commission. PIMAL was employed to model the relative positions of the ¹³¹I patient and members of the public in three exposure scenarios: (1) traveling on a bus in a total of six seated or standing permutations, (2) two nursing home cases where a caregiver is seated at 30 cm from the patient’s bedside and a nursing home resident seated 250more » cm away from the patient in an adjacent bed, and (3) two hotel cases where the patient and a guest are in adjacent rooms with beds on opposite sides of the common wall, with the patient and guest both in bed and either seated back-to-back or lying head to head. The biokinetic model predictions of the retention and distribution of ¹³¹I in the patient assumed a single voiding of urinary bladder contents that occurred during the trip at 2, 4, or 8 h after ¹³¹I administration for the public transportation cases, continuous first-order voiding for the nursing home cases, and regular periodic voiding at 4, 8, or 12 h after administration for the hotel room cases. Organ specific activities of ¹³¹I in the thyroid, bladder, and combined remaining tissues were calculated as a function of time after administration. Exposures to members of the public were considered for ¹³¹I patients with normal thyroid uptake (peak thyroid uptake of ~27% of administered ¹³¹I), differentiated thyroid cancer (DTC, 5% uptake), and hyperthyroidism (80% uptake). Results: The scenario with the patient seated behind the member of the public yielded the highest dose rate estimate of seated public transportation exposure cases. The dose rate to the adjacent room guest was highest for the exposure scenario in which the hotel guest and patient are seated by a factor of ~4 for the normal and differentiated thyroid cancer uptake cases and by a factor of ~3 for the hyperthyroid case. Conclusions: It was determined that for all modeled cases, the DTC case yielded the lowest external dose rates, whereas the hyperthyroid case yielded the highest dose rates. In estimating external dose to members of the public from patients with ¹³¹I therapy, consideration must be given to (patient- and case-specific) administered ¹³¹I activities and duration of exposure for a more complete estimate. The method implemented here included a detailed calculation model, which provides a means to determine dose rate estimates for a range of scenarios. Finally, the method was demonstrated for variations of three scenarios, showing how dose rates are expected to vary with uptake, voiding pattern, and patient location.« less

Authors:

Dewji, S. ^[1]; Bellamy, M. ^[1]; Hertel, N. ^[2]; Leggett, R. ^[1]; Sherbini, S. ^[3]; Saba, M. ^[3]; Eckerman, K. ^[1]

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+ Show Author Affiliations

1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Georgia Inst. of Technology, Atlanta, GA (United States)
3. US Nuclear Regulatory Commission (NRC), Washington, DC (United States)

Publication Date:

Wed Mar 25 00:00:00 EDT 2015

Research Org.:

Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USNRC

OSTI Identifier:

1185433

Grant/Contract Number:  

AC05-00OR22725; NRC-HQ-60-11-D-0024

Resource Type:

Accepted Manuscript

Journal Name:

Medical Physics

Additional Journal Information:

Journal Volume: 42; Journal Issue: 4; Journal ID: ISSN 0094-2405

Publisher:

American Association of Physicists in Medicine

Country of Publication:

United States

Language:

English

Subject:

60 APPLIED LIFE SCIENCES; 131I; thyroid; differentiated thyroid cancer; hyperthyroidism; public risk