Determination of Critical Organ Doses with 177Lu Prostate-specific Membrane Antigen Dosimetry in Metastatic Prostate Cancer Treatment

Aim: This study aimed to perform dosimetry in patients with metastatic prostate cancer treated with 177 Lutetium (Lu) prostate-specific membrane antigen (PSMA)-617 radiopharmaceutical, calculating organ blood clearance and consequently determining the maximum tolerable treatment activity. Materials and Methods: Eighteen patients with metastatic prostate cancer were enrolled in the study. Patients were administered 5.55 gigabecquerel (GBq) of 177 Lu-PSMA-617 radiopharmaceutical per treatment cycle through infusion. Blood samples (2 mL each) were collected at 2, 4, 6, 8, 18, 24, 36, and 44 h postinjection to assess the bone marrow absorbed dose. Organ doses were calculated using the OLINDA/EXM software based on scintigraphic images of the 18 patients who received 177 Lu-PSMA-617. Results: The blood clearance of 177 Lu-PSMA-617 radiopharmaceutical was determined to be bi-exponential. The mean absorbed doses for the parotid glands, kidneys, bone marrow, and liver were found to be 1.18 ± 0.27, 1.05 ± 0.3, 0.07 ± 0.05, and 0.31 ± 0.2 Gy/GBq, respectively. The radiation dose to the bone marrow was significantly lower than that to the kidneys and parotid glands. No dose limitations were necessary for kidneys and bone marrow in any of the patients. Conclusions: Our dosimetry results indicate that 177 Lu-PSMA-617 therapy is safe in terms of radiation toxicity.