The purpose of this article is to describe the analytical methods used to assess the internal dose from a P-32-labeled compound that was inadvertently ingested. Bioassay data, using the International Commission on Radiation Protection (ICRP)-30 model, enabled the calculation of internal dose. Whole body counting (WBC) and urinary measurement with liquid scintillation counting were utilized to estimate the amount of radioactive material deposited in body organs. This metabolic model assumes that 80% of the material ingested is absorbed through the gastrointestinal tract because P-32 is soluble. The time of the intake, a critical variable in this method, was estimated on the basis of urine contamination of clothing. Twenty-four-hour urine sampling over a 6-week period, coupled with daily WBC over the same period, was performed. Because P-32 does not emit photons, WBC relied on measuring the bremsstrahlung radiation produced as a result of interaction of beta radiation with the body's tissues. A P-32-spiked phantom was used as a control. Over the 6-week monitoring period, urinary results indicated an ingestion of 560 µCi of P-32, whereas WBC estimated an intake of 580 µCi. An assessment of the laboratory where the accident occurred indicated that approximately 600 µCi of radioactive phosphorous was missing. The total effective dose equivalent was estimated at 4.8 rem (48 mSv). On the basis of this study, the ICRP model appears to fit the data obtained from urine measurements and WBC. No symptoms were noted from the ingestion of 580 µCi. The committed organ doses were well within the occupational nonstochastic limits of 50 (0.5 Sv) permitted by the Nuclear Regulatory Commission. These results were confirmed by NUREG/CR-4884 and commercial software (CINDY). This report confirms the value of using the ICRP-30 model with urinary measurements and WBC to estimate the dose received as a result of ingestion of radioactive P-32.
From the Environmental Medical Service, Massachusetts Institute of Technology, Cambridge, Mass.
Address correspondence to: Robert J. McCunney, MD, MPH, Environmental Medical Service, Massachusetts Institute of Technology, 77 Massachusetts Ave, 16-267, Cambridge, MA 02139.