Diagnosis Performances And Impact On Therapeutic Strategy Of (18) F-Choline-Pet/Ct In Biochemical Relapse After I125 Brachytherapy For Localized Prostate Cancer

To assess patterns of uptake of (18) F-Choline-PET/CT (FCH PET/CT) and its diagnostic performances in case of biochemical relapse after I125 brachytherapy for localized prostate cancer. To evaluate how FCH PET/CT can guide the decision of implementation of prostatic biopsies and the salvage treatment. Between December 2012 and December 2016, 32 patients - previously treated by I125 brachytherapy according to NCCN recommendations - had a biochemical relapse based on ASTRO criteria and the Phoenix definition (nadir+2 ng/ml) and were referred to our center for FCH PET/CT. All imaging indications were validated in a multidisciplinary team meeting. The gold standard was defined by histology on prostatic biopsies. Patients were excluded if no gold standard was available. FCH PET/CT used a two-time protocol - 30 minutes after furosemide infusion - including dynamic pelvic acquisition immediately after 3 MBq/kg FCH and a later acquisition (> 10 minutes). Two experienced nuclear medicine physicians retrospectively recorded the following FCH PET/CT imaging prostatic characteristics: diffuse vs focal and peripheral vs central uptake, SUVmax from dynamic and late step and delta SUV absolute value (ΔSUV) - defined by the difference between late and dynamic SUVmax values. Statistical analysis used Student’s t test for SUVmax values and Fisher's exact test to compare ΔSUV results of true positive (TP) and false positive (FP) patients. Twenty-one patients reached histological gold standard. Mean time between I125 brachytherapy and FCH PET/CT was 64 months [23-120], mean PSA on the time of FCH PET/CT was 6.04 ng/mL [4.34-12.5] and mean PSA doubling time was 22.3 months [2.7-84.0]. Mean PSA value on the time of FCH PET/CT was respectively 3.9 ng/mL [1.07-8.00] and 4.3 ng/mL [2.1-9.2] for TP and FP patients (p=0.84). PSA doubling time was 21.6 months [5.2-84] for TP and 22.5 months [7.7-27.2] for FP (p=0,91). A central and diffuse uptake was constant - mean SUVmax=2.71 [1.9-5.8] - without any statistically significant differences between TP (mean SUVmax=2,82) and FP (mean SUVmax=2,58) (p=0.31). A peripheral uptake was found on 11 of 12 TP patients (mean SUVmax = 2.9 [2.3-3.9]). The ΔSUV>0.7 was correlated with histologically proven recurrence (p=0,01). Estimated sensitivity, specificity, predictive positive value, negative predictive value and accuracy were 1, 0.11, 0.6 [95% CI: 0.39-0.78], 1 [95% CI: 0.21-1] and 0.62 respectively. FCH PET/CT guided implementation of prostatic biopsies in 18 patients of 21 (85.7%) and salvage treatment in 47.6% of cases (4 prostatectomies, 4 HIFU and one multimodal treatment). A focal and peripheral prostatic uptake with ΔSUV>0.7 was correlated with recurrence after I125 brachytherapy. FCH PET/CT can guide the decision of implementation of prostatic biopsies and salvage treatment in case of histologically confirmed local recurrence.