Our first results suggested that (177)Lu-PSMA-617 therapy seems to be a safe method. The dose-limiting organ seems to be the parotid glands rather than kidneys and bone marrow. The lesion radiation doses are within acceptable ranges; however, there is a substantial individual variance so patient dosimetry seems to be mandatory.

Objective:The aim of the study was to estimate the radiation-absorbed doses and to study the in vivo and in vitro stability as well as pharmacokinetic characteristics of lutetium-177 (Lu-177) prostate-specific membrane antigen (PSMA)-617.Methods:For this purpose, 7 patients who underwent Lu-177-PSMA therapy were included into the study. The injected Lu-177-PSMA-617 activity ranged from 3.6 to 7.4 GBq with a mean of 5.2±1.8 GBq. The stability of radiotracer in saline was calculated up to 48 h. The stability was also calculated in blood and urine samples. Post-therapeutic dosimetry was performed based on whole body and single photon emission computed tomography/computed tomography (SPECT/CT) scans on dual-headed SPECT/CT system.Results:The radiochemical yield of Lu-177-PSMA-617 was >99%. It remained stable in saline up to 48 h. Analyses of the blood and urine samples showed a single radioactivity peak even at 24 hours after injection. Half-life of the distribution and elimination phases were calculated to be 0.16±0.09 and 10.8±2.5 hours, respectively. The mean excretion rate was 56.5±8.8% ranging from 41.5% to 65.4% at 24 h. Highest radiation estimated doses were calculated for parotid glands and kidneys (1.90±1.19 and 0.82±0.25 Gy/GBq respectively). Radiation dose given to the bone marrow was significantly lower than those of kidney and parotid glands (p<0.05) (0.030±0.008 Gy/GBq).Conclusion:Lu-177-PSMA-617 is a highly stable compound both in vitro and in vivo. Lu-177-PSMA-617 therapy seems to be a safe method for the treatment of castration-resistant prostate cancer patients. The fractionation regime that enables the longest duration of tumor control and/or survival will have to be developed in further studies.

The aim of this study is to investigate the outpatient treatment protocol and radiation safety of a new-emerging lutetium-177 ((177)Lu) prostate specific membrane antigen (PSMA) therapy. This work analyzed the dose rate of 23 patients treated with 7400 MBq (177)Lu-PSMA at different distances (0, 0.25, 0.50, 1.0 and 2.0 m) and variable time marks (0, 1, 2, 4, 18, 24, 48 and 120 h) after the termination of infusion. Blood samples were withdrawn from 17 patients within the same group at 3, 10, 20, 40, 60 and 90 min and 2, 3, 24 h after termination of infusion. Seven different patients were asked to collect urine for 24 h and a gamma well counter was used for counting samples. Family members were invited to wear an optically stimulated luminescence dosimeter whenever they were in the proximity of the patients up to 4-5 d. The total dose of the medical team including the radiopharmacist, physicist, physician, nurse, and nuclear medicine technologist was estimated by an electronic personnel dosimeter. The finger dose was determined using a ring thermoluminescent dosimeter for the radiopharmacist and nurse. The mean dose rate at 1 m after 4 h and 6 h was 23  ±  6 μSv h(-1) and 15  ±  4 μSv h(-1) respectively. The mean total dose to 23 caregivers was 202.3  ±  42.7 μSv (range: 120-265 μSv). The radiation dose of the nurse and radiopharmacist was 6 and 4 μSv per patient, respectively, whereas the dose of the physicist and physician was 2 μSv. The effective half life of blood distribution and early elimination was 0.4  ±  0.1 h and 5  ±  1 h, respectively. Seven patients excreted a mean of 45% (range: 32%-65%) from the initial activity in 6 h. Our findings demonstrate that (177)Lu-PSMA is a safe treatment modality to be applied as an outpatient protocol, since the dose rate decreases below the determined threshold of <30 μSv h(-1) after approximately 5 h and degrades to 20 μSv h(-1) after 6 h.

The effective half-life of iodine-131 for three patients was found to be 44 h. In conclusion, the amount of radioiodine excreted per hemodialysis session was calculated to be 51.25%.