11C-acetate PET/CT for prediction of negative lymph node involvement of prostate cancer before prostatectomy

1444 Objectives Accurate prediction of negative lymph node (LN) involvement is essential to facilitate the confidence and success of radical prostatectomy, particularly in patients with intermediate/high-risk prostate cancer (PCa). We aim to evaluate the value of 11C-acetate PET/CT for prediction of negative LN involvement in this group of patients before prostatectomy. Methods From July 2012 to June 2014, newly diagnosed PCa patients referred for 11C-acetate PET/CT were consecutively recruited. PET/CT was performed at 20 min post injection of ~550MBq 11C-acetate. Presence/absence of LN metastasis was evaluated by 2 nuclear medicine physicians in consensus. Patients with no LN involvement on 11C-acetate PET/CT and who underwent radical prostatectomy & pelvic LN dissection within 1 month after PET/CT were analyzed. Postoperative pathology served as the gold standard. Intermediate/high-risk patients were defined as those with: Gleason score (GS)=7 & serum PSA>=10ng/mL, GS>=8, or PSA>20ng/mL. Results 52 patients (age range:54~81y, mean=67.7±7.5y) showed absence of LN metastasis on 11C-acetate PET/CT and underwent radical prostatectomy & pelvic LN dissection within 1 month after imaging. 27/52 (52%) patients (mean age=68.7±7.1y, GS=7.2±1.0, PSA=29.8±15.3ng/mL) were classified as intermediate/high-risk and 25/52 (48%, mean age=66.5±8.1y, GS=6.2±0.4, PSA=7.9±2.2ng/mL) as low-risk. Histopathology revealed LN metastases in 3/27 (11.1%) intermediate/high-risk patients with 1 LN metastasis in each patient, and 0/25 (0%) low-risk patients. The accuracy for prediction of negative LN involvement in intermediate/high-risk and low-risk patients by preoperative 11C-acetate PET/CT was 88.9% and 100%, respectively. Conclusions 11C-acetate PET/CT has a high negative predictive value for LN involvement in newly diagnosed PCa patients with intermediate/high risk comparable to those with low risk. Inclusion of this imaging as part of preoperative work-up may facilitate the confidence and success of operative treatment for these patients.