Which radioactive drug hits tumors harder? small study aims to find out

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Male patient aged ≥60 years old at Visit 1 (Screening). * Patient has non-curative PSMA-positive prostate cancer that has spread outside of the prostate gland and is undergoing or being planned for radioligand therapy. * At least 1 PSMA-positive lesion that can be outlined on PET or CT and ≥1 cm in the short axis measured on either modality, for the purpose of dosimetry. * Adequate normal organ function as demonstrated by: * Absolute neutrophil count ≥1.5 × 109/L * Platelets ≥100 × 109/L * Haemoglobin ≥9 g/dL * Total bilirubin \<2 × the institutional upper limit of normal (ULN). For patients with known Gilbert's Syndrome, ≤3 × ULN is permitted. * Alanine aminotransferase (ALT) or aspartate transaminase (AST) ≤3.0 × ULN or ≤5.0 × ULN for patients with liver metastases. * Estimated glomerular filtration rate (using Chronic Kidney Disease Epidemiology Collaboration Creatinine Equation \[2009\]) \>50 mL/min. * Willing to provide signed and dated written informed consent form (ICF) prior to any study specific procedures * Male patients must agree not to father children or donate sperm during the study and for at least 14 weeks after the last study treatment. Exclusion Criteria: * Known hypersensitivity to lutetium (177Lu) rhPSMA 10.1 or lutetium (177Lu) vipivotide tetraxetan, or any of the constituents. * Previous treatment with any radiopharmaceutical therapy in the 42 days or 5 half-lives prior to Visit 1 (Screening). * Any significant metallic implants or objects, which may in the opinion of the investigator, affect image quality and/or dosimetry calculations. * Severe claustrophobia, inability to lie flat or fit into the scanner, or any other inability to tolerate the SPECT/CT scan protocol * Any change to prostate cancer medication or new prostate cancer therapy, prostate cancer surgical procedure within 42 days prior to screening or during the study. * Any medical or psychiatric condition, including rapidly progressive prostate cancer, that in the investigator's judgment, makes the patient unsuitable for the study * Participation in other studies involving other IMPs within 42 days or 5 half lives (whichever is longer) prior to Visit 1 (Screening) and/or during study participation