Clinical Experience of Stereotactic Ablative Body Radiation Therapy for the Treatment of Oligometastases Originating from Lower Gastrointestinal Primary Malignancies

Abstract

Current treatment options for the management of oligometastases originating from primary lower gastrointestinal (GI) malignancies include surgery, chemoradiotherapy and systemic therapy. Stereotactic ablative body radiotherapy (SABR) is being used with increasing frequency and has shown favourable clinical results. This study looks at the efficacy of SABR within this patient cohort in terms of overall survival (OS), progression-free survival (PFS) and short-term toxicity. A retrospective review of 52 patients with lower GI primary cancers who received SABR for oligometastases was conducted and end-points of OS and PFS were calculated. Toxicity data was also recorded. Assuming an α/ß ratio of 10 for tumour control, the biological equivalent doses (BED) of prescribed treatments were calculated. Patients who received a BED above and below the median were compared. A log-rank analysis was used to compare PFS between these groups according to primary tumour, site of metastases and dose fractionation. 52 patients with primary lower GI cancers (colon, rectum and anus) received SABR for the treatment of oligometastases between October 2013 and November 2016. 47 patients had extra-cranial metastases (lung, liver, lymph node, pelvic and bone) and 5 had intra-cranial metastases. Mean patient age was 64.2 years old. Mean follow-up was 15.7 months (95%CI 12.6-18.8). Mean OS for intra-cranial metastases was 5.1 months (95%CI 1.1-9.1). Mean OS and PFS for extra-cranial cases were 47.9 months (95%CI 44.3-51.5) and 26.0 months (95%CI 20.2-31.7) respectively. The median BED delivered was 69.3Gy (Range 37.5-151.2). No significant difference in PFS occurred when comparing primary tumour, site of metastases or dose fractionation. 19% of patients developed grade 1 or 2 toxicities within the first 12 months following treatment. Only a single grade 3 toxicity was reported.Abstract 2460Mean PFS (months) (95%CI)Site of primary (n)Colon (22)24.8 (18.0-31.6)Rectum (20)26.1 (16.7 -35.5)Anus (5)15.0 (7.9-22.1)P value0.604Site of extra-cranial metastases (n)Lung (3)13.9 (11.7-16.0)Liver (7)13.6 (6.4-20.8)Nodal (26)25.2 (19.1-31.4)Pelvic (8)23.9 (9.7-38.0)Bone (3)13.1 (6.1-20.1)P value0.878Dose fractionation (n)BED < 69.3Gy (22)25.2 (17.1-33.3)BED ≥ 69.3Gy (25)23.6 (17.0-30.1)P value0.557 Open table in a new tab The use of SABR in this cohort of patients with oligometastases from lower GI primary cancers has shown promising OS and PFS rates, irrespective of BED, primary site or location of metastases, with an excellent short-term toxicity profile.