PurposeWhole-body, regional planar, and SPECT imaging using the In-111–labeled monoclonal antibody capromab pendetide (In-111 MAb; ProstaScint) has been shown to increase the detection of early disease spread in patients with prostate cancer. However, recognition of metastatic tumor sites can be difficult, especially if the involved nodes are near blood vessels. We have developed an alternate approach to the identification of metastatic sites that is based on a single simultaneous In-111 MAb and Tc-99m RBC SPECT acquisition of the pelvis and abdomen on day 5 after injection. We have also developed software that dynamically subtracts the Tc-99m RBC data set (vascular component) from the In-111 MAb data set (prostate and lymph node component), which allows for easier identification of metastatic sites.MethodsWe evaluated the effectiveness of ProstaScint for staging 145 patients with prostate cancer, 19 newly diagnosed and 126 with recurrence, using these two modifications.ResultsWith clinical follow-up in 13 of 19 (68%) patients with primary disease, 10 of 13 (78%) had organ-confined disease. With follow-up in 64 of 126 (51%) patients with possible recurrent disease, 49 of 64 (77%) were found to have prostatic fossa activity only. Disease stage was deemed more advanced in 3 of 13 (22%) patients with primary cancer and in 13 of 64 (20%) of those with recurrent disease based on ProstaScint findings when all other imaging tests were inconclusive. Six patients with recurrent disease had negative results of their scans. In the 16 patients with more advanced disease, 3 of 59 lesions (5%) were documented as false positive, and there were no reported cases of false-negative findings.ConclusionsUsing both the dual-isotope procedure and the subtraction analysis software with the ProstaScint examination provides additional information for staging primary and possibly recurrent prostate cancer compared with standard imaging techniques.