Utility of 18F-Fluorocholine (FCH) PET/CT to Optimize Treatment Strategy and Radiation Therapy (RT) Planning in Patients with Biochemical Recurrence (BCR) of Prostate Cancer (PCa)

Abstract

RT is a main component in PCa therapy. After radical prostatectomy (RP), a rising PSA indicates PCa recurrence that may be cured with salvage radiotherapy (SRT). To maximize chances for cure, irradiated volumes should completely encompass the extent of disease. Thus, accurate estimation of disease extension is critical for RT planning in salvage setting. Integration of Positron Emission Tomography (PET) into routine evaluation of PCa patients (pts) may improve both staging accuracy and RT planning. 18F-fluorodeoxyglucose PET/CT is routinely used in radiation planning for several cancers. Additional PET probes, such as FCH, appear to be sensitive and specific in PCa. The objective of this study is to: (i) map the recurrence pattern of early BCR after RP, using FCH-PET/CT; (ii) determine how often volume definition decided prior PET/CT had to be modified to include pelvic and extra-pelvic diseases; (iii) assess the potential impact of FCH-PET/CT on SRT dose modification delivered to the site of recurrence. This study included 51 pts between 2011 and 2016. Median age was 62 (50-77) years. RP used robotic technology in 32 (62%) pts. All patients underwent FCH-PET/CT in a single institution before SRT at the time of BCR with PSA levels >/=0.16 ng/ml. Indications and RT volumes were systematically discussed in the multidisciplinary board meeting. The first definition of the CTV included either the prostate bed (PB) alone or PB + pelvic lymph nodes contoured on the simulation CT-scan dataset by a radiation oncologist blinded to the PET/CT results. PET/CT images were analyzed jointly by a nuclear medicine physician and radiation oncologist. FCH-positive lesions not covered by planning volumes based on the blinded CTV were considered to have a major potential impact on treatment planning. After RP, 9 (17%) pts had T3, Gleason >7 or N+. Median PSA at time of FCH-PET/CT was 1.4 (0.16-37) ng/mL. 19 of 51 (37%) pts had a positive FCH-PET/CT at BCR. The detection rate of FCH uptake was significantly higher in pts with PSA≥0.5ng/mL than in those with PSA <0.5ng/mL (p<0.008). Among the 19 pts with positive FCH-PET/CT, 9 (47%) had at least one metastatic site not covered by the blinded CTV, 6 (31%) had extra-pelvic lesions while 5 (26%) had FCH-positive lesions within the pelvis but not covered by the blinded CTV. The two most common FCH-positive lesion locations outside the blinded CTV were bone (26%) and perirectal lymph nodes (37%). The rate of total RT volume changes was 13/19 (68%). Finally, 2 (10.5%) pts had PB uptake that needed an increased SRT dose up to 70Gy. We confirm that FCH-PET/CT can allow better lesions mapping at the time of BCR. At least one-third of the patients had positive FCH-PET/CT with a trend of significance after a PSA level of 0.5ng/mL. When metastatic disease is detected, FCH uptake changed SRT planning in more than 2/3 of patients. Further investigations and longer follow-up are needed to assess the impact of these changes on outcome.