Objective
We investigated the role of integrated [11C]choline PET/CT for target volume selection and delineation in patients (pts) with recurrent prostate cancer following EBRT for a salvage focal Cyberknife Stereotactic Hypofractionated Radiotherapy (SBRT).
Methods and Materials
From December 2012 through December 2016 33 pts with initial disease category defined as low (7), intermediate (8), high (18), in accordance with NCCN 2008 guidelines, a median age of 74 years (range 62-89) and an history of locally-recurrent prostate cancer following EBRT were referred to our Department for salvage Cyberknife SBRT.
Restaging at biochemical failure was based on CT Scan, Bone Scan and [11C]choline PET/CT. Median ipsa was 19.6 ng.ml (4.9 - 88 ng.ml) , EBRT doses ranged from 74 to 79.2 Gy (median 76 Gy) and the median interval time between diagnosis of prostate cancer relapse and salvage focal Cyberknife treatment was 66 months (range 12-187). The median pre-reirradiation PSA was 4.84 ng.ml (range 2.23 - 21.04 ng.ml).
To reconstruct CTV and organ at risk, CT scan and MRI with T1-T2 sequences were performed and [11C]choline PET/CT images were fused for prostate target volume definition and delineation.
9 pts received 3 fractions of 10 Gy (total dose 30 Gy), 24 pts received 3 fractions of 12 Gy (total dose 36 Gy) delivered to the PET positive prostate node (median volume of 14.3 cc - range 5.75-65.04).
Results
Salvage Focal Cyberknife treatment was well tolerated without any symptoms related to RTOG G3 GU or GI acute or late toxicity. With a median follow up of 26 months (range 7-49) we observed the following results: no in field recurrence, resulting in a local control of 100%. In 6 pts, a [11C]choline PET/CT detect the presence of a local recurrence (median time 15 months; range 8-22) with the evidence of a new positive prostate focal node outside the irradiated field requiring a second Cyberknife salvage treatment. 3 pts develop lymph nodes or bone metastases 6, 9 and 12 months after Cyberknife treatment.
Conclusions
Focal approach to the ablation of the index lesion using [11C]choline PET/CT fusion for image guidance is a suitable technique for partial prostate dose escalation. According to available literature that has not established a standardized strategy to plan target volume, nevertheless, our promising data suggest a potential role of [11C]choline PET/CT as an image guide tool for the irradiation of focal prostate cancer relapse.
