Radiation levels of patients with metastatic castration-resistant prostate cancer treated with 177Lu-PSMA-617

Purpose: 177Lu-PSMA-617 has been demonstrated to be an effective radiopharmaceutical for the treatment of mCRPC, it’s necessary to investigate the discharge protocol and radiation safety as a new-emerging targetting prostate specific membrane antigen (PSMA) therapy in China. This study aimed to investigate the levels of external radiation and urine activity of patients underwent 177Lu-PSMA-617 therapy, and to provide reference data for developing the measures of radiation protection and discharge guidelines in the future in China.

Methods/Materials: The radiation levels of 14 patients underwent 177Lu-PSMA-617 were monitored in this study with administration of an average of 7.34±0.36 GBq of 177Lu-PSMA-617 each procedure. The ambient dose equivalent rates of most patients were monitored from the body surfaces to 1 m distance at 6 points (Anterior and posterior positions of the chest, abdomen, and pelvis) with a well calibrated portal gamma dose rate survey meter (AT1123, ATOMEX) at time points of 0h, 1h, 2h, 4h, 6h and 24h after the administration. The activity of 177Lu in urine was measured with a calibrated activity meter (CRC-25R, CAPINTEC).

Results: The averaged dose rates at 1 m away from the body surface ranged from 13.4 μSv/h to 25.3 μSv/h, with an average of (19.6±3.8) μSv/h after 6h of administration on 11 patients, and an average of (8.8±3.3) μSv/h with range from 4.6 μSv/h to 15.2 μSv/h for all of the 14 patients after 24h. In addition, the averaged dose rates further reduced to about 6.4±1.6 μSv/h for the 2 patients after 48 h. The maximum dose rates at 5cm, 30cm and 50cm away from the patients after 24h of administration could reach 273 μSv/h, 80 μSv/h and 52 μSv/h, respectively. In 6h after injection, the activity of 177Lu excreted in urine ranged from 10.5% to 48.7%, with a median value of 25%, and the maximum excretion fraction could be 9.6% after 24h.

Conclusions: Our preliminary measurements indicated that the averaged dose rates at 1 m away from the body surface of patients are generally lower than 20 μSv/h and 10 μSv/h after 6 h and 24 h of administration. More data on 177Lu activity in the urine are desired for further evaluation of radiation protection and discharge in the future in China.