Evaluation of the contamination risk during 177Lu-PSMA therapy of advanced prostate cancer

Introduction: The recent FDA-approval of ¹⁷⁷Lu-PSMA-617 for radiopharmaceutical therapy (RPT) of metastatic, castration-resistant prostate cancer will lead to rapidly availability of this treatment in different centers and vastly increasing patient numbers. In Germany, ¹⁷⁷Lu-PSMA therapy is performed during an in-patient stay of 48h. This offers the possibility to monitor contamination which may occur given the patients comorbidities as well as urinary incontinence. The aim of this investigation was to quantify the contamination risk in patient rooms during ¹⁷⁷Lu-PSMA therapy to assess the risk of radiation exposure for the nuclear medicine personnel.

Methods: Wipe samples were taken from representative surfaces in the patient rooms such as door handles, toilet seat, faucet, and chairs at 24h and 48h post-injection of the radiopharmaceutical. The samples were measured in a gamma counter and a calibration factor for ¹⁷⁷Lu was applied to yield the amount of activity per sample in Becquerel. The activities were decay corrected to the time point of sample collection. All floors were further screened for possible contamination using a hand-held contamination monitor for beta minus particles and gammas triggering further wipe samples and surface measurements in case a contamination was detected.

Results: Measurements were performed for 19 ¹⁷⁷Lu-PSMA treatments. Median injected activities were 7.39 ± 1.01 GBq. A total of 180 samples was analyzed. The maximum detected activity for the representative surfaces was 46.70 kBq, with a median activity of 0.16 kBq. Generally, the highest contaminations were found on the toilet seats, followed by door handles and faucets. A localized contamination of the floor was detected in 79% (15 out of 19) of the therapies with a maximum of 5163.60 kBq/m² and a median activity of 69.40 kBq/m².

Conclusions: Our data indicate a contamination risk associated with ¹⁷⁷Lu-PSMA RPT. Non-negligible contaminations were found in patient washrooms and on the floor. While surface contaminations were low, a high floor contamination poses the risk of an unintended dispersion and demands cautious decontamination measures. The results also indicate uncontrolled radiation exposure for family caregivers and the overall population when the treatment is performed in an outpatient setting. Further extended analysis of post-treatment contaminations are warranted to tailor specific radiation protection measures. This will moreover increase the safety for the patient during treatment and minimize the risk of contamination and radiation exposure for personnel.

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