77 Background: 11C or 18F-labeled choline PET/CT has led to better understanding of the lymph drainage pattern of prostate cancer. It can provide radiation oncologists with maps to guide the delivery of prophylactic pelvic radiotherapy while minimizing radiation toxicity to non-target normal tissue with intensity modulated radiation therapy (IMRT). The purpose of this study was twofold: (1) to describe the pattern of nodal relapse in prostate cancer patients with biochemical failure after prostate-only radiotherapy; and (2) to determine whether patients with 18F-fluoro-choline (FCH) PET/CT positive nodes experienced treatment failure within the clinical target volume (CTV) defined by the RTOG guidelines (CTVRTOG). Methods: Between July 2008 and December 2012, 83 patients with a prostate cancer had a FCH PET/CT for biochemical failure after radiotherapy. Of 65 patients with FCH-positive findings, 33 had positive nodes. This analysis included 31 patients who had undergone prior prostate-only radiotherapy or radical prostatectomy followed by local radiotherapy. Each choline FCH positive node was assigned to a lymph node station and situated with regard to the CTVRTOG. 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 two or more positive nodes on FCH PET/CT. Patients with FCH+ nodes outside the CTVRTOG were more likely than patients with FCH+ nodes inside the CTVRTOG to have two or more involved nodes (OR= 8.75, [95% CI: 1.38-54.80], p= 0.020). The ventral part of the external iliac station (29.0%) was the main site of relapse inside the CTVRTOG whereas relapses that occurred outside the CTVRTOGinvolved the proximal common iliac (19.3%) and lower periaortic nodes (19.3%) up to L2-L3. Conclusions: Nearly half of the patients had FCH+ nodes outside the CTVRTOG with a significantly higher number of nodes involved outside the CTVRTOG. Three-dimensional 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.
Early Biochemical Relapse After Radical Prostatectomy: Which Prostate Cancer Patients May Benefit from a Restaging 11C-Choline PET/CT Scan Before Salvage Radiation Therapy?