Measuring the Radiation Exposure Risk of 89Zr for PET/CT Imaging

For patients with clear cell renal cell carcinoma (ccRCC), ⁸⁹Zr-girentuximab (⁸⁹Zr) is emerging as a popular radionuclide to use in positron emission tomography/computed tomography (PET/CT) imaging. While the ZIRCON study previously evaluated its performance in the detection of ccRCC, safety procedures for health care providers working with the radionuclide have not yet been established.

At the 2024 Society of Nuclear Medicine and Molecular Imaging Annual Meeting, Adnan Chowdhury, MSc, MPhys, presented data from a new study to guide the assessment of the radiation risk of ⁸⁹Zr and establish necessary control procedures.

The study took place at a single site, where a quantitative radiation dose rate was measured from the drug vial, a controlled spill, and a patient. Researchers recorded dose rate measurements 0.05, 0.50, and 1.00 meters from the ⁸⁹Zr vial and 1.00 meter from a 1 mL-controlled spill on an absorbent surface.

A patient enrolled in the ZIRCON study was administered 37 MBq of ⁸⁹Zr, and dose rate measurements were taken at 3 distances from the patient’s anterior (surface, 1, and 2 meters) at 5 time points: immediately following infusion (day 0), at hour 2 on day 0, day 3, day 4 before surgery, and day 4 after surgery. The patient underwent radical nephrectomy on day 4, and radiation dose rates were measured from the surgically removed kidney, surgical equipment, and waste.

The dose rate from a vial of ⁸⁹Zr at 1 meter was 0.20 µSv/hr/MBq, while the rate from a controlled spill at 1 meter was 0.52 µSv/hr/MBq. Immediately after infusion, the dose rate at the patient’s surface was 85 µSv/hr. At 1 and 2 meters from the patient, the dose rates were 4.0 and 1.5 µSv/hr, respectively.

At day 3, the dose rates from the patient’s surface, 1, and 2 meters were 34.0, 3.1, and 1.0 µSv/hr, respectively. On day 4 before surgery, the dose rates from the patient’s surface and at 1 meter were 15 and 3 µSv/hr, respectively.

The dose rate from the patient kidney on day 4 was 6 µSv/hr at 5 cm. After surgery on day 4, the dose rates from the patient’s surface, 1, and 2 meters were 12.0, 2.5, and 0.6 µSv/hr. The surgical equipment used had a low level of contamination, and surgical waste did not measure higher than background radiation.

The use of ⁸⁹Zr PET/CT and subsequent surgery in patients treated with it demonstrated low radiation exposure levels. As the patient studied underwent radical nephrectomy 4 days after ⁸⁹Zr administration, with patient surgery occurring 20.5 ± 20.1 days (mean ± SD) after administration in the ZIRCON study, the radiation measurements represented the upper end of the range of expected dose to surgery theater staff.

Since recent positive phase 3 trial results point to the potential integration of ⁸⁹Zr into clinical practice, appropriate radiation protection procedures are needed for physicians. This study’s dose rate measurements can help guide the development of best practices.

Watch Rana McKay, MD, of the University of California San Diego, share commentary on the study’s findings here: https://guoncologynow.com/post/safety-considerations-for-89zr-girentuximab-pet-ct-imaging-in-ccrcc.