Internal Dose Assessment for the Patient in 131I Misadministration Accident Based On the Individual-Specific Biokinetics and Korean Reference Models
T Kwon1*, M Park2, M Cho2, (1) National Cancer Insitute, Rockville, MD, (2) Korea Institute of Radiological and Medical Sciences, Seoul, South Korea
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PO-GePV-I-75 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: To estimate the internal doses of the Korean patient (adult male) to whom ¹³¹I-iodide solution of 5.55 Gq was accidently administered, considering the incompleteness of the thyroid blocking and the Korean physiological/anatomical characteristics.
Methods: We first monitored the patient’s thyroid four times over the period of more than two months after the misadministration using an electrically cooled high-purity germanium spectrometer. We then determined the patient-specific iodine binding rate in the thyroid, which was associated with the thyroid blocking, by statistical fitting of the monitoring results and the predicted thyroidal iodine. We also calculated S-values for ¹³¹I based on Mesh-type Reference Korean Phantom coupled with the ¹³¹I disintegration numbers calculated from the Korean iodine biokinetic model. Internal doses were calculated for 28 target organs/tissues.
Results: Contrary to the International Commission on Radiological Protection (ICRP) reference data (binding rate for thyroid blocking = 0 d⁻¹), the patient-specific iodine binding rate was determined as 0.30 d⁻¹ (p=0.093) indicating that the thyroid blocking was not complete. The S-value for thyroid self-absorption was approximately 1.5-fold greater than the ICRP reference value due to smaller thyroid masses of Koreans. As a result, the thyroid absorbed dose of the patient was 36.3 Gy, 3-fold greater than that based on the ICRP Publication 128 dose coefficient.
Conclusion: We calculated the internal doses of the patient who underwent ¹³¹I misadministration using the patient-specific biokinetic parameters and the Korean reference models. We found up to 3-fold underestimation of the thyroid dose when ICRP Publication 128 data are used. The methodology and the results of this work will be applied to various dose assessment cases in nuclear medicine for more accurate and reliable dosimetry.
Funding Support, Disclosures, and Conflict of Interest: This study was supported by a grant from the Korea Institute of Radiological and Medical Sciences (KIRAMS), funded by Ministry of Science, ICT and Future Planning, Republic of Korea
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