Feasibility of salvage focal nodal SBRT or protracted elective nodal irradiation in 18F fluoro-choline PET based nodal failures from prostate cancer.

Abstract

290 Background: 1) To establish the feasibility of salvage nodal radiotherapy in patients with 18F Fluoro-choline (FCH) PET+ nodal recurrence only from a prostate cancer. 2) To compare salvage focal FCH PET+ stereotactic radiation therapy (sf-SRT) with salvage elective nodal irradiation with a protracted FCH PET+ nodal boost (seni-PRT) . Methods: Between 2009 and 2014, 42 patients out of 102 patients with FCH PET for a rising PSA after RP or radiotherapy had positive lymph nodes only. Twenty nine patients had sf-SRT and 13 patients had seni-PRT in a curative intent. Acute and late genito urinary (GU) and gastro intestinal (GI) toxicities were assessed with CTCAE v4. Failure was defined as a rising PSA higher than the maximal pre-therapeutic PSA value followed by 2 consecutive rises or a nodal or distant metastatic failure or the initiation of any salvage therapy. Results: Seventy-six nodes were diagnosed with FCH PET/CT with a median PSA value of 2.8 [0.3 -29.2] at time of failure. Mean number of nodes was higher in the seni-PRT group than in the sf-SRT group (2.8 vs 1.6). The median prophylactic dose of WPRT and/or LA was 48.0 Gy [36.0-54.0] and the median dose delivered to involved FCH PET+ nodes was 66.0 Gy [46.0-70.0] with a median dose per fraction of 2.0 [1.8-2.2]. In the sf-SRT group, the median dose to the involved nodes was 36 Gy [18-45] with a median dose per fraction of 7.5 Gy [6-15]. After a median follow-up of 19.1 months [2.9-74.1], no difference was observed for GI or GU toxicities between the 2 groups (p = 0.26 and p = 0.19). One grade 4 GI and GU toxicity occurred in 1 patient in the seni-PRT group. The median freedom from failure (FFF) time was 14.8 months for sf-SRT and 37.6 months for seni-PRT with 2-year FFF rates of 47.8 % and 72.7 %, respectively. Conclusions: FCH PET+ node-targeted salvage radiotherapy is feasible with very low rates of toxicity. Freedom from failure was significantly improved with protracted elective nodal irradiation, suggesting that nodal disease diagnosed on FCH PET may not be an oligometastatic disease. Dose escalated seni-PRT is currently being investigated in a French phase II trial (Oligopelvis- GETUG P07).