The Impact of a Negative 111Indium-Capromab Pendetide Scan Before Salvage Radiotherapy

Abstract

We determined the prognostic role, if any, of the ProstaScint (111)indium-capromab pendetide scan before salvage radiotherapy for biochemical recurrence after RP for localized prostate cancer. We reviewed the records of 649 patients who underwent a ProstaScint scan from 1998 to 2004. A total of 44 patients were identified who had biochemical recurrence after RP and underwent a ProstaScint scan immediately before salvage radiotherapy. All patients received salvage radiotherapy to the prostatic bed unless pelvic lymph node uptake was identified on the scan, resulting in initial whole pelvic radiotherapy with 45 Gy, followed by a conformal boost to the prostate bed in 6. The median salvage radiotherapy dose to the prostate bed was 72 Gy. Patient demographics, pathological information, PSA values and ProstaScint results were collected retrospectively. The majority of ProstaScint scans were digitally fused with noncontrast pelvic computerized tomography images for interpretation. PSA progression after radiotherapy was defined using American Society for Therapeutic Radiation and Oncology criteria. At a mean followup of 22 months 43 of 44 patients (97%) experienced a PSA decrease after salvage radiotherapy with a mean PSA nadir of 0.16 ng/ml compared to a mean pre-radiotherapy PSA of 1.7 ng/ml. Of the 44 patients 15 (34%) showed post-radiotherapy PSA progression. When the entire cohort was analyzed, patients with negative ProstaScint scans had statistically lower post-radiotherapy PSA progression rates than patients with positive scans (1 of 10 or 10% vs 14 of 34 or 41%, p = 0.026). Patients with negative ProstaScint results were also statistically more likely to have a pre-radiotherapy PSA of less than 1.0 ng/ml (p = 0.005), no seminal vesicle involvement (p = 0.006), a greater mean PSA doubling time (p = 0.008) and received no hormone therapy (p = 0.003). When patients with pre-radiotherapy PSA less than 1.0 ng/ml were analyzed, a negative ProstaScint scan suggested but did not provide a statistically significant advantage over pre-radiotherapy PSA alone for predicting post-radiotherapy PSA progression (1 of 9 or 11% for negative vs 5 of 15 or 33% for positive scans, p = 0.20). Our early experience supports an improved prognosis in patients receiving salvage pelvic radiotherapy for biochemical recurrence after RP who have a negative pre-radiotherapy ProstaScint scan. However, this finding is not necessarily independent of pre-radiotherapy PSA.