Stereotactic Body Radiotherapy for Management of Pulmonary Oligometastases in Stage IV Colorectal Cancer: A Perspective

Abstract

In pulmonary oligometastases from colorectal cancer (POM-CRC), metastasectomy is the primarily recommended treatment. Stereotactic body radiotherapy (SBRT) has been suggested as a viable alternative therapy. SBRT efficacy for POM-CRC is poorly delineated compared to selected non-CRC primaries. This perspective article aims to critically summarize the existing evidence regarding efficacy of SBRT in terms of overall survival (OS) and local control (LC), and factors modulating this, in the treatment of POM-CRC. Overall, reasonable LC and OS rates were observed. The wide range of expansions in planning target volume margins introduced variation in pretreatment protocols. Dose-fractionation schedules varied according to patient and tumor characteristics, though leverage of BED₁₀ in select studies enabled standardization. An association between SBRT dose and improved OS and LC was observed across multiple studies. Prognostic factors that were associated with improved LC included: fewer oligometastases, absence of extra-pulmonary metastases, primary tumor histology, and smaller gross tumor volume. Differences in SBRT modality and techniques over time further confounded results. Many studies included patients receiving additional systemic therapies; preprotocol and adjuvant chemotherapies were identified as prognostic factors for LC. SBRT compared with metastasectomy showed no differences in short-term OS and LC outcomes. In conclusion, SBRT is an efficacious treatment for POM-CRC, in terms of OS and LC. Heterogeneity in study design, particularly pertaining to dose protocols, patient selection, and additional therapies should be controlled for future randomized studies to further validate SBRT efficacy.