Comparison of 177Lu-PSMA-617 and 225Ac-PSMA-617

This trial compares two types of targeted radiation therapy for prostate cancer that has spread (metastatic prostate cancer): one using lutetium-177 (177Lu-PSMA-617) and a more potent version using actinium-225 (225Ac-PSMA-617). Both drugs seek out a protein on prostate cancer cells called PSMA and deliver radiation directly to the tumor. Researchers want to see which is more effective and better tolerated. **You may be eligible if...** - You have metastatic prostate cancer that expresses the PSMA protein (confirmed by a special scan) - Your cancer has progressed despite previous treatments - Your overall health and organ function are adequate for treatment - You are 18 or older **You may NOT be eligible if...** - Your cancer does not express PSMA - You have significant kidney disease or poor bone marrow function - You have received prior PSMA-targeted radiation therapy - You have active brain metastases or severe other illnesses Talk to your doctor to see if this trial is right for you.