Cancer-specific dose and fractionation schedules in stereotactic body radiotherapy for oligometastatic disease: An interim analysis of the EORTC-ESTRO E2-RADIatE OligoCare study

Background and introduction: Optimal dose and fractionation in stereotactic body radiotherapy (SBRT) for oligometastatic cancer patients remain unknown. In this interim analysis of OligoCare, we analyzed factors associated with SBRT dose and fractionation. Materials and methods: Analysis was based on the first 1,099 registered patients. SBRT doses were converted to biological effective doses (BED) using alpha/beta of 10 Gy for all primaries, and cancer-specific alpha/beta of 10 Gy for nonsmall cell lung and colorectal cancer (NSCLC, CRC), 2.5 Gy for breast cancer (BC), or 1.5 Gy for prostate cancer (PC). Results: Of the interim analysis population of 1,099 patients, 999 (99.5 %) fulfilled inclusion criteria and received metastasis-directed SBRT for NSCLC (n = 195; 19.5 %), BC (n = 163; 16.3 %), CRC (n = 184; 18.4 %), or PC (n = 457; 47.5 %). Two thirds of patients were treated for single metastasis. Median number of fractions was 5 (IQR, 3-5) and median dose per fraction was 9.7 (IQR, 7.7-12.4) Gy. The most frequently treated sites were nonvertebral bone (22.8 %), lung (21.0 %), and distant lymph node metastases (19.0 %). On multivariate anal