Long-Term Survival and Local Control Outcomes in Oligometastatic Colorectal Cancer Treated with Liver Stereotactic Body Radiation Therapy

Abstract

The purpose of the present study was to evaluate clinical outcomes following stereotactic body radiation therapy (SBRT) in patients with liver metastases (LM) due to colorectal cancer (CRC). This was a single-institution retrospective study of patients included in a prospectively maintained institutional database. Outcome endpoints included overall survival (OS) and local control (LC). We also performed assessments for predictors of LC and OS including evaluation of BED10 less than or greater than 150. Eligible patients had LM due to CRC, were treated with SBRT between 2007-2018, and had at least 3 months of follow up. Median SBRT dose was 54 Gy (range 32-60 Gy) in 3 fractions (range 3-5), and median BED10 was 151.0 Gy. All survival times were calculated from the start date of SBRT. Kaplan-Meier curves were used to estimate actuarial survival times, and Cox regression was used for multivariable analysis (MVA) of predictors of OS. We identified 67 eligible patients and 15/67 (22%) of patients had prior partial hepatectomy. Median number of chemotherapy regimens prior to SBRT was 1 (range 0-3). The majority of patients (79.6%) had a solitary liver metastasis; 2 had extrahepatic disease at the time of SBRT. The maximum number of treated LM was 3. Median tumor diameter was 2.7 cm (range 0.4-5.6). At a median follow up of 42.5 mos (range 3-96), 27/67 patients (40.2%) of patients had died. The median estimated OS (KP method) in this patient cohort was 64.0 months (95% CI 41.6 - Not Estimable (NE)). Estimated median KP duration of local control was 71.4 months (95% CI: 38.5, NE) in the entire patient cohort. Duration of local control was statistically significantly better in patients with liver SBRT treatment where the BED was > 150. The median duration of LC in patients with liver SBRT plans with BED10 > 150 was 74.4-months (95% CI: 40.1, NE) vs 26.1 month (95%: CI 11.6 – NE) in those with liver SBRT plan with BED < 150 (p=0.0006). The median KP estimated OS was 82.4 months (95% CI: 41.4 – NE) in patients with SBRT plan > 150 vs 62.8 months (95% CI: 36.2 mo. – NE) in those with BED < 150 (p= 0.697). Duration of local control was found to significantly correlate with OS. The hazard of death was reduced by 5.1% for each additional month of local control. GTV size (cc), diameter of treated metastases, and presence of K-ras mutation did not appear to be a predictor of LC in our patient cohort. SBRT is very effective in the management of hepatic oligometastases and was associated with an estimated median OS greater than 5 years in select patients. In this study, we found that duration of local control was significantly associated with overall survival. Additionally, it appears from this series that BED10 > 150 is associated with increase in local control.