Author: Colin Adam Doyle, Celeste Winters 👨🔬
Affiliation: Department of Diagnostic Radiology, Oregon Health & Science University, School of Medicine, Oregon Health & Science University 🌍
Purpose: To audit our radioactive iodine (I-131) dosimetry protocol, review dosimetry methods used at other facilities, investigate the clinical impact of I-131 dosimetry at our facility, and test the validity of simplified methods.
Methods: Dosimetrically calculated maximum tolerated activity (MTA) was compared to the administered activity for I-131 dosimetry patients at OHSU from 2016 - 2024. Methods used by other clinics were pulled from the SNMMI Radioiodine Dosimetry Initiative Dosimetry Database and organized into a table which included state or country name, number of clinics in each region, and the dosimetry methods used. A literature review was completed to understand and summarize each dosimetry method methods were used on past patient data, and MTA results were compared to dosimetry results from the time of treatment.
Results: Of the 16 I-131 dosimetry patients at OHSU from 2016 – 2024, dosimetry indicated a limited MTA in three patients based on 2 Gy to the blood. In patients with a higher calculated MTA, one received 250 mCi, seven received 220 mCi, two received 200 mCi, and four received below 200 mCi.
Only 20 (30.7%) of the clinics in the SNMMI database report their dosimetry methods. Of those 20, eight use Benua-Leeper, seven use Simplified or Sisson, and five clinics use both methods.
On a test patient, MTA was calculated as 455 mCi for the blood and 373.1 mCi for the lungs using the Benua-Leeper method, 501 mCi for the blood using an updated Benua-Leeper method (MIRD Primer 2020), “no modification” using the Sission method, and 257 mCi using the Attkins method.
Conclusion: This study highlights the lack of not just standardized I-131 dosimetry, but the practice of I-131 dosimetry in general. The comparison and testing of dosimetry methods resulted in our clinic using the updated Benua-Leeper method, as outlined in the MIRD Primer.