Pattern of occult nodal relapse diagnosed with (18)F-fluoro-choline PET/CT in prostate cancer patients with biochemical failure after prostate-only radiotherapy.

Introduction: The purpose of this study was to describe the pattern of nodal relapse with (18)F-fluoro-choline (FCH) Positron Emission Tomography/Computerized Tomography (PET/CT) in prostate cancer patients after radiotherapy.

Materials And Methods: Eighty-three patients had a FCH PET/CT at time of biochemical failure. Of 65 patients with positive findings, 33 had positive nodes. This analysis included 31 patients who had undergone prior prostate-only radiotherapy with or without a prior radical prostatectomy. Each FCH positive node was assigned to a lymph node station with respect to the CTV defined by the RTOG guidelines (CTVRTOG). 3D mapping was performed after each node was manually placed in a reference planning CT scan after automatic co-registration of the two scans based on bone anatomy. Eighteen patients (58%) underwent focal salvage FCH PET-guided stereotactic radiotherapy with no hormones.

Results: Fourteen patients (45.2%) had a relapse outside the CTVRTOG. Of the 17 patients with a positive node inside the CTVRTOG, 15 had a single node (88.2%) while seven patients out of the 13 evaluable patients (53.9%) who had a relapse outside the CTVRTOG had ⩾2 positive nodes on FCH PET/CT (OR=8.75, [95% CI: 1.38-54.80], p=0.020). Relapses that occurred outside the CTVRTOG involved the proximal common iliac (19.3%) and lower periaortic nodes (19.3%) up to L2-L3.

Conclusion: 3D mapping of nodal relapses evaluated with FCH PET/CT suggests that with IMRT the upper field limit of pelvic radiotherapy could be extended to L2-L3 safely to cover 95% of nodal stations at risk of an occult relapse.