Robotic stereotactic radiotherapy for liver oligometastases from colorectal cancer: a single-center experience

Purpose: To report on the safety and clinical benefit of robotic stereotactic radiotherapy (SBRT) for liver oligometastatic colorectal cancer (CRC). Methods: Robotic SBRT was applied to oligometastatic CRC patients, defined as having 1–4 liver metastases and absent or controlled extrahepatic disease. The intended prescription dose was 37.5 Gy in three fractions. Treatment efficacy was estimated by clinical benefit rate (CBR), progression-free survival (PFS) and overall survival (OS). Toxicity was graded according to CTC-AE scale, v. 4.03. Regression analysis was performed to search for the presence of any predictive factors. Results: Between 2012 and 2017, 38 patients (66 lesions) were irradiated. The median delivered biological effective maximum dose (maxBED10) was 142 Gy. At a median follow-up of 11.8 months (range 3.2–58.8), the 1- and 2-year OS were 67.3% and 44.1%, respectively. Actuarial LC rates for all patients at 6 and 12 months were 64.2% and 60.4%, respectively. Local or distant progression occurred in 28 (77.8%) patients, with a 1- and 2-year PFS of 19.3% and 12.2%, respectively. The CBR was 71.4%, with no significant association with maxBED10. At multivariate analysis, the presence of extrahepatic disease had a detrimental impact on PFS (HR 3.98, 95% CI 1.77–8.93; p < 0.001) and OS (HR 3.58, 95% CI 1.06–12.07; p < 0.04). No acute grade 3 gastrointestinal toxicity was observed. Conclusions: Our analysis underlines the importance of patients’ selection to identify the oligometastatic scenario most likely to benefit from SBRT. Prospective studies are needed to further assess its role among locoregional treatment options for liver metastases from CRC.