68Ga-PSMA PET/CT for Ra223 Assessment

It is a open-label single-arm clinical trial. Outcome measurement is the positivity rate of Ga68-PSMA-11 PET-defined progression and Bone Scan-defined progression. The primary objective is to compare the diagnostic positivity in progression of PSMA PET and BS. The 2×2 contingency table with four diagnostic outcomes (both positive, PET positive/BS negative, PET negative/BS positive, and both negative) will be conducted based on the enrolled subjects. Both diagnostic tools (Ga68-PSMA-11 PET and BS) are applied to a given set of individuals. Since both diagnostic tools will performed on each subject, then paired data result and methods that account for the correlated binary outcomes are necessary. McNemar's test will be used to compare the positivity of the two tools. Assuming that Ga68-PSMA-11 PET in patients detect more metastatic lesions/progression by 26.5% (i.e. p10-p01=0.265) and the discordant percentage is 38.5 % (i.e. p10+p01=0.385). Under the hypothesis H0: p10=p01, achieving an 80% power at the 5% of significance level, the sample size is 44. Based on expecting 15% of missing rate, the adjusted sample size will be 52. This calculation was done by PASS software (Power Analysis and Sample Size version 11.0.8, NCSS, Kaysville, Utah, USA).

For PET/CT PSMA scan, the subject will have catheter(s) placed for intravenous administration of \[68Ga\]PSMA-11. Subjects will receive a single intravenous bolus of 2-5 mCi \[68Ga\]PSMA-11 and received PET/CT scan 60 minutes later. PSMA PET-CT scan was performed on a GE Discovery MI PET/CT system. The CT scan parameters were 120 kVp, 30 mA to 300 mA acquired with auto mA , 40× 0.625 collimator configuration, and pitch of 0.984 : 1. All images were reconstructed with a 500 mm field of view and a slice thickness of 5 mm. The PET acquisition time was 3 mins per bed position with maximum overlap (35 slices). Images were reconstructed using Q clear with beta value of 550, PSF correction, and non-TOF (QCHD-S). The matrix is 256 × 256. After image acquisition, the subject will be observed for half an hour, and will be discharged if no adverse event happens. EKG, blood and biochemistry test will be performed before and after first PET scan no more than two weeks. Except baseline Ga68-PSMA-11 PET/CT scan, patients will receive serial PET scans after 3rd injection of Ra-233 and 6th injection of Ra-223. All of the images were interpreted by an experienced nuclear medicine physicians.