Session Item

Up to 40% of patients with pelvic primary will present a locoregional recurrence in a previously irradiated area. Stereotactic ablative body radiotherapy (SABR) re irradiation can be proposed for treatment of oligometastatic relapse. The aim of the study was to report the clinical outcome after SABR re irradiation in patients presenting an extra bone oligometastatic relapse from pelvic cancer.

This is a retrospective monocentric study including patients who benefited from salvage SABR in a previously irradiated pelvic area from January 2011 to February 2018. Patients with intra-prostatic or bone relapse were not included.

A total of 30 patients were treated with SABR, the most frequent primary tumor sites were rectum (30.8%), prostate (30.8%) and anal cancer (19.2%), and the most frequent re irradiated site was iliac node (40%).  With a median follow-up of 29.4 months (1-50) there were three (10%) acute grade 3 (G3) toxicity and no late G3-5 toxicity. At 12 and 24 months, LFRS, MFRS, PFS and OS were respectively 67.7%/50.7 %, 67%/ 41.7%, 34.8%/14.9% and 83.2%/62.5%. Univariate analysis revealed local control improvement in low GTV (<10mL) (p=0.003) and prostate primary (p=0.02). This was however not confirmed in multivariate analysis. Of note vicinity of target with organ at risk did not significantly correlate with worse toxicity profile (p=0.14) or worse tumor coverage (GTV: p=0.8, PTV: p=0.4).

SABR pelvic re irradiation in oligometastatic patients appeared as a safe and effective procedure in this cohort. Local control was good and the pattern of relapse was more often distant relapses. Tumor size appeared to influence oncologic and toxicity outcome and should be taken account before re irradiation.