Negative HIV test at screening Negative serum pregnancy test at screening A negative pregnancy test (if female) FOCBP must have a negative pregnancy test =< 7 days prior to registration on study Negative serum pregnancy test Negative serum pregnancy test within 7 days prior to starting treatment FOCBP must have a negative pregnancy test within 7 days prior to registration on study Female patients must have a negative pregnancy test A negative serum pregnancy test FOCBP must have a negative pregnancy test within 7 days prior to registration on study; NOTE: a negative pregnancy test is also required within 3 days prior to first dose of pembrolizumab and therefore may need to be repeated if screening test is more than 3 days prior to first dose And have a negative serum pregnancy test at screening Negative serum pregnancy test In female, a negative pregnancy test if experiencing menstrual periods. Negative serum pregnancy test at screening have a negative serum pregnancy test at the time of enrollment, Women of child bearing potential (WOCBP) must have a negative serum pregnancy test within the 7 days prior to investigational product administration and a negative urine pregnancy test within the 3 days prior to the first investigational product administration, or a negative serum pregnancy test within the 3 days prior to the first investigational product administration Negative serum pregnancy test. FOCBP must have a negative pregnancy test within 7-10 days prior to receiving study drug Has a negative serum pregnancy test within 7 days prior to starting treatment. FOCBP must have a negative pregnancy test =< 7 days prior to registration on study And have a negative serum pregnancy test ? 10 days of cycle 1, day 1 (C1D1) For WoCBP* negative serum pregnancy test within 7 days of enrollment. In female, a negative pregnancy test if experiencing menstrual periods FOCBP must have a negative pregnancy test within 7 days prior to registration\r\n* Note: FOCBP will have to have repeat pregnancy test within 24 hours of starting nivolumab, scheduled for cycle 1 day 1 Negative serum pregnancy test have a negative serum pregnancy test at screening and before Betalutin injection A negative Hepatitis B test (HBsAg and anti-HBc) and negative HIV test during screening Negative serum pregnancy test Negative serum pregnancy test Negative pregnancy test Negative pregnancy test at the time of SRS in any patient who could be pregnant Pregnancy or breastfeeding; female patients who are post-menarchal must have a documented negative pregnancy test Negative pregnancy test, if applicable A negative serum pregnancy test (if female and aged between 18-55 years old). Negative pregnancy test FOCBP must have a negative pregnancy test =< 7 days prior to registration Negative pregnancy test A negative pregnancy test (if female). Negative serum pregnancy test WOCBP must have a negative serum pregnancy test within 14 days prior to the first dose of ipilimumab/nivolumab A negative serum pregnancy test (if female and aged between 18-55 years old). Documentation of negative pregnancy test. Must have a negative serum pregnancy test Negative pregnancy test at screening Negative serum pregnancy test; if, on cycle 1 day 1, greater than 72 hours has elapsed since the last negative result, a serum pregnancy test must be repeated and be negative on cycle 1 day 1 (C1D1) for the patient to remain eligible Negative serum pregnancy test at screening. Negative serum pregnancy test within 7 days of commencement of treatment in premenopausal women Negative pregnancy test for WOCBP Negative pregnancy test (if female in reproductive years) Negative pregnancy test. Negative pregnancy test (if female in reproductive years) Negative pregnancy test if applicable Subjects with reproductive potential must have a negative pregnancy test within 14 days before randomization And have a negative blood pregnancy test at the time of screening And have a negative serum pregnancy test at screening Negative serum test for pregnancy in premenopausal women Negative serum pregnancy test. Post-menarchal female has had negative serum pregnancy test within 7 days prior to enrollment Women must have a negative serum pregnancy test A negative serum pregnancy test (if female and aged between 18-55 years old). WOCBP must have a negative serum pregnancy test within 7 days prior to receiving investigational product and a negative urine pregnancy test on Day 1 of each Cycle; A negative serum pregnancy test (if female) Negative pregnancy test Negative pregnancy test Negative pregnancy test Negative pregnancy test Negative pregnancy test negative serum pregnancy test Negative pregnancy test FOCBP must have a negative pregnancy test within 14 days prior to registration on study Must have a negative serum pregnancy test at screening and day -1, and Negative pregnancy test at study registration Negative pregnancy test Negative pregnancy test They are not pregnant (i.e., female patients must have a negative serum pregnancy test at screening); Pregnancy, confirmed by a negative pregnancy test within 30 days of study enrollment All WOCBP MUST have a negative pregnancy test prior to first receiving study medication Negative pregnancy test =< 7 days prior to randomization has a negative pregnancy test on the day of vaccination, and has a negative pregnancy test on the day of vaccination, and Pregnancy or nursing patients will be excluded from the study; a pregnancy test will be done prior to the MR examination for postmenarchal teenage girls, in whom pregnancy may be possible; only patients with a negative pregnancy test will be included in the study Pregnancy or nursing patients will be excluded from the study; a pregnancy test will be done prior to the MR examination for postmenarchal teenage girls, in whom pregnancy may be possible; only patients with a negative pregnancy test will be included in the study Determination of pregnancy status: Female patients who are not postmenopausal or surgically sterile will undergo a serum pregnancy test prior to each set of [18F]FLT and [18F] Fluciclovine PET scans; a negative test will be necessary for such patients to undergo research PET imaging In female patients, negative pregnancy test with no plans to become pregnant during the duration of the study Female patients who are not postmenopausal or surgically sterile will undergo a serum pregnancy test prior to the research PET scans; the serum pregnancy test must be performed within 48 hours prior to the initial research PET imaging; a negative test will be necessary for such patients to undergo research PET imaging Determination of pregnancy status: female patients that are not postmenopausal or surgically sterile will undergo a serum pregnancy test prior to each set of multi-tracer PET scans; a negative test will be necessary for such patients to undergo research PET imaging Negative serum pregnancy test Female patients who are not postmenopausal or surgically sterile will undergo a serum pregnancy test prior to baseline and the subsequent set of multi-tracer PET scans; the serum pregnancy test must be performed within 48 hours prior to research PET imaging; a negative test will be necessary for such patients to undergo research PET imaging Determination of pregnancy status: female patients who are not postmenopausal or surgically sterile will undergo a serum pregnancy test prior to baseline and the subsequent set of multi-tracer PET scans; the serum pregnancy test must be performed within 48 hours prior to research PET imaging; a negative test will be necessary for such patients to undergo research PET imaging