Effects of maximum dose on local control after stereotactic body radiotherapy for oligometastatic tumors of colorectal cancer

This study aimed to identify radiotherapy dosimetric parameters related to local failure (LF)free survival (LFFS) in patients with lung and liver oligometastases from colorectal cancer treated with stereotactic body radiotherapy (SBRT). We analyzed 75 oligometastatic lesions in 55 patients treated with SBRT between January 2014 and December 2021. There was no constraint or intentional increase in maximum dose. LF was defined as the progression of the treated lesion until the last follow-up or death. The dose distributions were recalculated using Monte Carlo-based algorithms. The significance of the planning target volume (PTV) biologically effective dose (BED) 10s (D2, D95, D98, Dmean) in LFFS was evaluated using Cox regression, considering sex, age, primary cancer, tumor site, oligometastatic status, multiplicity, and either tumor size or one of the volume parameters. LF occurred in 23.4% of the lesions. Lesions showing LF received significantly lower PTV D2 (146 ± 21 vs. 164 ± 23, p = 0.006). Multivariate analysis revealed that PTV D2 (< 159 Gy₁₀ vs. ≽ 159 Gy₁₀) was the sole dosimetric parameter associated with LFFS. Tumors equal to or larger than the median size/volume yet receiving < 159 Gy₁₀ of PTV D2 showed the lowest LFFS following stratification by median PTV D2 combined with tumor size or volume parameters. The maximum dose (PTV D2) was significantly associated with LFFS after SBRT for lung and liver oligometastases from colorectal cancer. Increasing the maximum dose may be beneficial for managing larger tumors.