Local control assessment following SABR for lung metastases of colorectal cancer: A multicenter retrospective analysis.

Objectives: Stereotactic ablative radiotherapy (SABR) is a relevant option for the radical treatment of lung metastases from colorectal cancer with insufficient local control in some cases. The aim of this study is to determine the dosimetric and clinical predictive factors affecting the efficacy of SABR in treating lung metastases from colorectal cancer.

Materials And Methods: Patients with lung metastases from colorectal cancer treated with SABR in 8 centers between August 2016 and January 2023 were consecutively reviewed. Clinical and dosimetric parameters were evaluated as predictive factors for freedom from local relapse (FFLR), overall survival (OS), and time to polymetastatic conversion (tTPC).

Results: A total of 309 lesions from 201 patients were analyzed. With a median follow-up time of 31 months, the 2-year FFLR and OS were 69.5 % and 80.8 % respectively. Treated Tumor Volume (TTV, corresponding to either GTV or ITV) biological effective dose (BED) near to the minimum (TTV BEDmin) ≥ 110 Gy (HR 0.48, 95 % CI 0.3-0.79, p = 0.003), number of previous metastatic systemic treatment before SABR (NPT) ≥ 2 (HR 2.08, 95 % CI 1.25-3.45, p = 0.004) and the left side origin (HR 0.55, 95 % CI 0.33-0.91, p = 0.02) were significantly associated with FFLR in multivariate analysis. The 2-year FFLR rates were 56.2 % (95 % CI 43.9 %-72.1 %) and 73.1 % (95 % CI 66.8 %-80 %) for lesions treated with TTV BEDmin < 110 Gy and ≥ 110 Gy respectively (p = 0.007). For lesions with a NPT before SABR of 0-1 and NPT ≥ 2, the two-year FFLR rate was 73.2 % (95 % CI 67.1 %-79.9 %) and 51.8 % (95 % CI 37.9 %-70.8 %) respectively (p = 0.02). For lesions from the left and the right side, the two-year FFLR rate was 72.9 % (95 % CI 66.6 %-79.7 %) and 53.4 % (95 % CI 40.3 %-70.8 %) respectively (p = 0.02). For OS, age (HR 1.03, 95 % CI 1.01-1.06, p = 0.007) and the presence of ≥ 4 total lung metastases (4.44, 95 % CI 1.3-15.2, p = 0.017) were independent prognostic factors for OS in multivariate analysis. For tTPC, synchronous metastasis (HR 1.93, 95 % CI 1.08-3.44, p = 0.025) and the number of total lung metastases ≥ 4 (HR 7.3 95 % CI 2.2-23.7, p < 0.001) were significantly associated with tTPC in multivariate analysis.

Conclusion: This study highlights the prognostic significance of the TTV BEDmin dose delivered to the tumor and identifies prior treatment as a risk factor for local relapse, while a left-sided primary tumor origin is associated with improved local control.