Preliminary experience with dosimetry, response and patient reported outcome after (177)Lu-PSMA-617 therapy for metastatic castration-resistant prostate cancer

Prostate cancer can be targeted by ligands to the prostate-specific membrane antigen (PSMA). We aimed to evaluate dosimetry, safety and efficacy of (177)Lu-PSMA-617 radioligand therapy (RLT) in patients with metastatic castration-resistant prostate cancer (mCRPC). Fifteen patients each received two cycles of 3.7 GBq (n = 5) or 6.0 GBq (n = 10) (177)Lu-PSMA-617 at an eight to ten weeks interval. For safety monitoring, each treatment was followed by dosimetry with serial quantitative SPECT as well as inpatient and outpatient recording of adverse events. Response to RLT was primarily determined by baseline to follow-up change in (68)Ga-PSMA PET/CT (RECIST1.1), as well as change in prostate-specific antigen (PSA), quality of life (QoL, FACT-P scale), and pain (Brief Pain Inventory) as secondary endpoints. Radiation dose delivered to the tumor (6.1 Gy/GBq) was six to twelve-fold higher than to critical organs (kidney left/right 0.5/0.6 Gy/GBq each, salivary glands 1.0 Gy/GBq). Total radiation dose per kidney did not exceed 23 Gy in any patient. Three patients had sub-acute and latent grade 3 events, i.e. anemia, leukocytopenia, and nausea. No acute events, grade ≥4 events or high grade events for salivary gland or kidney function were observed. After two RLT cycles, 4 (27%) patients had partial response, 6 (40%) had stable disease, and 5 (33%) had progressive disease according to RECIST. Any PSA decline was observed in 12/15 (80%) patients during RLT. Significant pain relief was documented in 7/10 (70%) symptomatic patients and QoL improved in 9/15 (60%) patients. (177)Lu-PSMA-617 therapy proved safe and indicated promising response rates for both objective and patient-reported outcomes in our small group of mCRPC patients.