11C-acetate PET/CT in pre-therapeutic lymph node staging in high-risk prostate cancer patients and its influence on disease management - a retrospective study

Background: Radiation treatment with simultaneous integrated boost against suspected lymph node metastases may be a curative therapeutic option in patients with high-risk prostate cancer (> 15% estimated risk of pelvic lymph node metastases according to the Cagiannos nomogram). C-11-acetate positron emission tomography/computed tomography (PET/CT) can be used for primary staging as well as for detection of suspected relapse of prostate cancer. The aims of this study were to evaluate the association between positive C-11-acetate PET/CT findings and the estimated risk of pelvic lymph node metastases and to assess the impact of C-11-acetate PET/CT on patient management in high-risk prostate cancer patients. Methods: Fifty consecutive prostate cancer patients referred for primary staging with C-11-acetate PET/CT prior to radiotherapy with curative intention were enrolled in this retrospective study. Results: All patients showed increased C-11-acetate uptake in the prostate. Pelvic lymph node uptake was seen in 42% (21/50) of the patients, with positive external iliac lymph nodes in 71% (15/21) of these. The overall observed proportion of PET/CT-positive pelvic lymph nodes at patient level was higher than the average estimated risk, especially in low-risk groups (< 15%). There was a significant association between observed proportion and estimated risk of pelvic lymph node metastases in groups with <= 45 and >45% estimated risk. Treatment strategy was altered due to C-11-acetate PET/CT findings in 43% (20/47) of the patients. Conclusions: The observed proportion of C-11-acetate PET/CT findings suggestive of locoregional metastases was higher than the estimated risk, suggesting that the Cagiannos nomogram underestimates the risk for metastases. The imaging results with C-11-acetate PET/CT have a considerable impact on patient management.