A Multicenter Large Retrospective Database on the Personalization of Stereotactic Ablative Radiotherapy for Lung Metastases From Colon-Rectal Cancer: The LaIT-SABR Study

PURPOSE/OBJECTIVE(S): stereotactic ablative radiotherapy (SABR) has been shown to increase survival rates in oligometastatic disease (OMD), but local control of colorectal metastases still remains poor. We aimed to identify potential predictive factors of SBRT response through a multicenter large retrospective database and to investigate how lung SBRT can impact on the progression to the polymetastatic disease (PMD). MATERIALS/METHODS: the study involved 22 centers, and was approved by the Ethical Committee (Prot. Negrar 2019-ZT). 1023 lung metastases treated with SBRT in 622 patients were reported. The median BED was 105 Gy10. Lesion diameter GTV, PTV volume, dose, fractionations, and site of primary tumor were evaluated as potential predictive marker for SBRT response for the primary end-point local progression-free survival (LPFS). EGFR, KRAS, NRAS, BRAF, and MSI were also evaluated. Secondary end-point was the time to the polymetastatic conversion (ttPMC). RESULTS: the median follow-up was 26 months (range 3-117 months). The median lesion diameter was 13 mm (range 4-58 mm). The 2- and 3-year LPFS were 75.6% and 71%, respectively. At the univariate analysis, BED ≥125Gy10 was associated with improved LPFS (2-year: 94.1% versus 72.6%; P = < 0.0001), single fraction SBRT correlated with better LPFS in the overall population (2-year: 80.6% versus 73.7%; P = 0.03), but no significant difference was observed when considering the population treated with BED > 100 Gy10. Lesion diameter ≤19 mm correlated with improved LPFS (2-year 80% versus 60%; P = < 0.0001). The median ttPMC was 26 months, and the 2-year ttPMC was 54.5%. The median PFS was 11.3 months. After SABR, 36% patients had polymetastatic relapse, 39.5% patients had an oligometastatic relapse, and 24.5% patients had no further relapse. CONCLUSION: the present is the largest series of lung colorectal metastases treated with SABR. The results support the use of SBRT in lung oligometastatic colorectal cancer patients as it might delay the transition to PMD or offer relatively long disease-free period in selected cases. Several biological and clinical predictive factors were identified to assure the highest local control, on the basis of which a decisional algorithm will be derived.