PROSTATE-CANCER AND PROSTATE BED SPECT IMAGING WITH PROSTASCINT(R) - SEMIQUANTITATIVE CORRELATION WITH PROSTATIC BIOPSY RESULTS

BACKGROUND. ProstaScint(R) (Cytogen Corporation, Princeton, NJ) murine monoclonal antibody imaging is FDA-approved for imaging of prostate c ancer patients at high risk for metastatic disease and patients postpr ostatectomy with a rising serum prostate-specific antigen (PSA) level. ProstaScint(R) is a murine monoclonal antibody which targets prostate -specific membrane antigen (PSMA). PSMA expression is upregulated in p rimary and metastatic prostate cancer. FDA Cytogen (Princeton, NJ) pro tocol studies using (111)indium-labeled ProstaScint(R) revealed correl ation between areas of increased concentration in the prostate and bio psy-proven humors in patients imaged pretherapy. METHODS. in our study , four transverse, single-photon emission tomography (SPECT) images we re isolated and regions of interest were selected and correlated with pretherapy prostate biopsy results. Prostate cancer and normal tissue prostate/muscle background (P/M) ratios were derived, so that postpros tatectomy/radiation therapy patients could be evaluated for the presen ce of residual prostate cancer. Twenty-three pretherapy prostate cance r patients with quadrant/sextant biopsies had SPECT 96-hr (111)indium ProstaScint(R) pelvic images. The four transverse 1-cm slices above th e midline penile blood pool were chosen, and four to six 27-30-pixel r egions of interest were placed over the prostate bed. The background m uscle region of interest was placed over the external obturator muscle region. The P/M ratio was calculated and compared to the quadrant/sex tant prostatic biopsy result. The same procedure was applied to 17 pos ttherapy prostate cancer patients with rising PSA. RESULTS. In the 23 pretherapy prostate cancer patients, there was a correlation between t he P/M ratio of at least 3.0 in 32 of 35 prostatic cancer biopsy regio ns, and there was correlation with P/M ratios less than 3.0 in 82 of 8 9 negative biopsy regions. Seventeen posttherapy patients underwent Pr ostaScint(R) studies. Six underwent biopsy, with typically one biopsy site per patient. All 6 had P/M ratios greater than 3.0 in the biopsie d region. Five out of six biopsies revealed residual prostate cancer. CONCLUSIONS. A prostate/muscle ratio was developed from (111)indium Pr ostaScint(R) regions of interest obtained on 1-cm SPECT transverse sli ces through the prostate bed in 23 patients preprostatic cancer therap y. A P/M ratio above 3.0 correlated in the majority of positive cases, and a P/M ratio below 3.0 was demonstrated in negative prostatic biop sy cases. The P/M ratio of above 3.0 or below 3.0 also separated those posttherapy prostate cancer patients with rising PSA who had residual prostate carcinoma in the prostate bed. (C) 1998 Wiley-Liss, Inc.