Effect of primary tumor location and tumor size on the response to radiotherapy for liver metastases from colorectal cancer.

Metastatic liver tumors (MLTs) from colorectal cancer (CRC) are often treated with stereotactic body radiation therapy (SBRT). The present study aimed to examine the predictive factors for response of MLTs to SBRT. A total of 39 MLTs from 24 patients with CRC were retrospectively analyzed. Radiotherapy for MLT was typically performed with a prescribed dose equivalent to a biologically effective dose (BED)10 of 100 Gy. The median follow-up period was 16 months (range, 5-64 months). The median prescribed dose and total BED10 were 56 Gy (range, 45-72 Gy) and 97.5 Gy (range, 71.7-115.5 Gy), respectively, in a median of 8 fractions (range, 4-33 fractions). The 1- and 2-year local control rates were 67.2 and 35.9%, respectively. For patients with MLT treated with ablative SBRT (BED10 ≥100 Gy in ≤5 fractions), the 1- and 2-year local control rates were 83.3 and 62.5%, respectively. Univariate analysis showed that primary tumor location (left-sided colon), maximum tumor diameter (≤30 mm) and ablative SBRT (BED10 ≥100 Gy in ≤5 fractions) were significantly associated with improved local control (P=0.0058, P=0.0059 and P=0.0268, respectively). Multivariate analysis showed that tumor diameter was significantly associated with improved local control (P=0.0314). In addition, patients who received ablative SBRT had significantly prolonged overall survival times compared with those treated with non-ablative SBRT (P=0.0261). To conclude, tumors ≤30 mm that can be treated with ablative SBRT are associated with good local control rates. The primary tumor location may affect the radiosensitivity of MLTs.