Stereotactic Ablative Body Radiotherapy to Treat Colorectal Oligometastases

Abstract

To assess the outcome of all patients with primary colorectal cancer who received SABR (stereotactic ablative body radiotherapy) for oligometastatic disease under the Commissioning through Evaluation program at our institution over a three-year time period. Data were collected retrospectively from our institutional SABR database. All patients with primary colorectal cancer who received SABR to oligometastases (one to three lesions) between 01.01.2016 and 01.01.2019 were included. Patients were treated using a TrueBeam linear accelerator. 19 oligometastases were treated in 16 patients. 13 patients received SABR to one metastasis and three patients had two metastases treated. The median age of patients was 69.5 years (range 36 to 87 years); 11 patients (68.8%) were male and five patients (31.2%) female. Nine patients (56.3%) had a primary colon cancer and seven patients (43.7%) had a primary rectal cancer. 10 (62.5%) patients received treatment to a separate metastasis prior to SABR. The site of metastases treated included 12 (63.2%) lung metastases, 6 (31.6%) lymph node metastases, and 1 (5.2%) liver metastasis. The median biologically effective dose (BED10) delivered was 115.5Gy (range 60 to 151.2Gy). The median follow up was 20.5 months (range 6 to 37 months). No patients experienced grade 3 to 4 toxicity following SABR. 8 (50.0%) patients are currently alive and disease free. Four patients (25.0%) developed local recurrence of their metastasis. The mean time to local recurrence was 10.5 months; three of these patients (75.0%) had a primary rectal cancer and one patient (25.0%) had a primary colon cancer. Three patients (18.8%) developed distant recurrence following SABR. The mean time to distant recurrence was five months; one of these patients had a primary rectal cancer (33.3%) and two patients (66.6%) had a primary colon cancer. Of note one patient developed both local and distant recurrences. Two patients (11.1%) died during the follow up period. This study demonstrated a local failure rate of 25.0% following SABR to colorectal oligometastases within a 20.5 month median follow up. Patients with a rectal primary appeared to have a higher local failure rate (42.9%) than those with a primary colon cancer (11.1%). There was no evidence that SABR adversely affected the quality of life in these patients. Colorectal metastases have a radioresistant phenotype and have been associated with higher local failure rates following SABR compared with different tumor histologies. This potentially highlights the need for dose escalation within this cohort of patients particularly in patients with rectal primaries.