Radiation protection considerations following administration of zirconium-89 labeled tracers: are patient restrictions necessary?

The increasing use of zirconium-89 (89Zr) labeled radiopharmaceuticals has highlighted a lack of guidance regarding post-administration radiation restriction advice. This study aimed to estimate cumulative radiation exposure to close contacts following 37 MBq 89Zr administration and to evaluate the need for radiation restriction advice. Published dose rate measurements following administration of 89Zr-girentuximab were used to model cumulative exposure using physical decay only. Contact modeling incorporating realistic social and domestic patterns was adapted from established methodologies. Radiation restriction durations required to maintain exposure below the 300 µSv public dose constraint were determined iteratively for several contact groups. The same methodology was applied to fluorine-18 fluorodeoxyglucose (18F-FDG) at 400 MBq for comparison. Without restrictions, all contact groups exceeded the 300 µSv dose constraint. Estimated cumulative doses were highest for partners (4552 µSv) and infants under 2 years (4516 µSv). Restriction durations to reduce cumulative dose below the constraint were 14 days for partners and infants, 11 days for children aged 2-5 years, 8 days for children aged 5-11 years, 3 days for work colleagues, and 2 days for other adults. No restrictions were necessary for 18F-FDG administration. Restriction durations following 89Zr-girentuximab administration were longer than anticipated from administered activity or dose rate measurements alone. By contrast, 18F-FDG required no restrictions, highlighting the importance of physical half-life and emission energy in determining cumulative contact exposure. These findings highlight the importance of contact modeling and provide a practical framework for developing evidence-based radiation restriction advice following 89Zr imaging.