11C-choline PET/CT detects the site of relapse in the majority of prostate cancer patients showing biochemical recurrence after EBRT.

PURPOSE: The aim of this retrospective study was to evaluate the usefulness and the detection rate of (11)C-choline PET/CT in a population of patients with prostate cancer (PC), exclusively treated with external beam radiotherapy (EBRT) as primary treatment, who showed biochemical relapse.

MATERIALS AND METHODS: We enrolled 140 patients showing a serum PSA level >2 ng/mL (mean 8.6 ng/mL, median 5 ng/mL, range 2 - 60 ng/mL). All patients had been treated with EBRT to the prostate gland and prostatic fossa with doses ranging from 70 to 76 Gy in low-risk patients (T1/T2 and/or serum PSA <10 ng/mL) and escalating to >76 Gy (range 76 - 81 Gy) in high-risk patients (T3/T4 and/or serum PSA >10 ng/mL). Of the 140 patients, 53 were receiving androgen deprivation therapy at the time of the scan. All positive (11)C-choline PET/CT findings were validated by transrectal ultrasound-guided biopsy or at least 12 months of follow-up with contrast-enhanced CT, MR, bone scintigraphy or a repeated (11)C-choline PET/CT scan. The relationships between the detection rate of (11)C-choline PET/CT and the factors PSA level, PSA kinetics, Gleason score, age, time to relapse and SUV max in patients with positive findings were analysed.

RESULTS: (11)C-Choline PET/CT detected the site of relapse in 123 of the 140 patients with a detection rate of 87.8 % (46 patients showed local relapse, 31 showed local and distant relapse, and 46 showed only distant relapse). In patients with relapse the mean serum PSA level was 9.08 ng/mL (median 5.1 ng/mL, range 2 - 60 ng/mL), the mean PSA doubling time was 5.6 months (median 3.5 months, range 0.4 - 48 months), and the mean PSA velocity was 15 ng/mL/year (median 8.8 ng/mL/year, range 0.4 - 87 ng/mL/year). Of the 123 patients with relapse, 77 (62.6 %) showed distant relapse with/without local relapse, and of these 77, 31 (40.2 %) showed oligometastatic disease (one or two distant lesions: lymph node lesions only in 16, bone lesions only in 14, and lymph node lesions and bone lesions in 1). In univariate and multivariate analyses PSA kinetics was the only variable affecting (11)C-choline PET/CT detection rate. A significant correlation between PSA kinetics and site of recurrence (local relapse only vs. distant metastasis) was also observed.

CONCLUSION: The detection rate of (11)C-choline PET/CT in patients with PC showing biochemical recurrence after EBRT as primary treatment is relatively high (87.8 %). (11)C-Choline PET/CT was able to detect extraprostatic disease in the 62.6 % of patients. Considering this high detection rate, (11)C-choline PET/CT could have clinical usefulness in the management of these PC patients, but this should be confirmed in future studies.