Schedule De-Escalation of 177Lu-PSMA-617 for the Treatment of Metastatic Castrate Resistant Prostate Cancer

Inclusion Criteria: * REGISTRATION INCLUSION CRITERIA * Scheduled at Mayo Clinic Rochester for therapy with 177Lu PSMA-617 * PSMA positive metastatic castration resistant prostate cancer (68Ga and 18F PSMA PET will be considered equivalent for eligibility) , defined by molecular imaging prostate specific membrane antigen (miPSMA) score \>= 2 on Mayo PET report, including interpretation of outside PET or consensus review of PET by nuclear therapy tumor board note in the patient chart * Willingness to provide mandatory blood draws for correlative research. (This requirement is waived for patients enrolling after receiving cycle 1 of 177Lu PSMA-617,and achieving a near complete response on post therapy SPECT, as these patients will not be able to provide a pre-treatment baseline blood sample.) * Provide written informed consent * Ability to complete questionnaire(s) by themselves or with assistance * Willing to return to enrolling institution for follow-up (during the active monitoring phase of the study) * RANDOMIZATION INCLUSION CRITERIA * Lesions with uptake equal to or above liver on cycle 1 post therapy SPECT, demonstrating that a near complete response on follow up post-therapy scan represents response, rather than sensitivity differences between SPECT and pre-treatment PET * Near-complete response on post-therapy SPECT following any of cycles 2-5 of 177Lu PSMA-617. Near-complete response will be defined as no lesions with SUV max above the mean standard uptake value (SUV…