ESTRO 2024 - Abstract Book

S1704

Clinical - Lung

ESTRO 2024

Purpose/Objective:

Radical treatment of oligometastatic and oligoprogressive disease is a major issue of stereotactic ablative radiotherapy (SABR) development, particularly in colorectal cancer. The aim of this study is to determine the impact of dosimetric and clinical parameters on local control of lung metastasis from colorectal cancer treated by SABR.

Material/Methods:

Patients with lung metastatic colorectal cancer treated by SABR in 6 French centers between August 2016 and January 2023 have been consecutively reviewed. Analyses were performed on the entire cohort and on the cohort of oligometastatic patients (i.e. excluding oligoprogressor patients). Clinical, biological and dosimetric parameters were evaluated as predictive for local control (LC) on both cohorts, and time to polymetastatic conversion (TPC) only on the oligometastatic cohort. Due to the heterogeneity of practices and dose reporting across centers, Gross Tumor Volume (GTV) and Internal Target Volume (ITV) were combined into a single entity called Treated Tumor Volume (TTV). Three dosimetric parameters were converted to biological effective dose (BED) using an α/β ratio of 10 Gy for each TTV and Planning Target Volume (PTV) doses: (1) the near-minimum dose (BEDmin); (2) the near maximum (BEDmax); and (3) the mean-dose (BEDmean).

Results:

For the entire cohort (lesions=285; patients=185), median follow-up was 56 months. Median age was 73 years. LC at two years was 77.5%. In univariate analysis, a TTV BED 10 min ≥110 Gy was significantly associated with an increase of LC (HR=0.46, 95% CI 0.26-0.8, p=0.006), while a number of previous metastatic systemic treatments before SABR (NPT) ≥2 and a total number of lung metastasis ≥4 were associated with a worse LC (HR=2.11, 95% CI 1.21 -3.69, p=0.008 ; HR=2.57, 95% CI 1.16-5.7, p=0.02 respectively) . The two-year LC rate for lesions treated with TTV BED 10 min <110 Gy and ≥110 Gy were 65% and 80.9% (p=0.007) respectively ( Figure 1 ), and 81.5% and 63.9% (p=0.02) for lesions with NPT 0- 1 and NPT ≥2 (p=0.02) respectively. In multivariate analysis, the parameters significantly correlated with LC were TTV BED 10 min ≥110 Gy (HR=0.45, 95% CI 0.27 - 0.75, p=0.0025) and NPT ≥2 (HR=2.02, 95% CI 1.2-3.43, p=0.008) ( Figure 2 ). The G3 pulmonary toxicity rate was 0.7 %. No G4-5 was observed. For the oligometastatic cohort (lesions=250; patients=163), the LC rate in univariate analysis showed the same statistically significant parameters except for the total number of lung metastasis. In multivariate analysis, the parameters significantly correlated with LC were TTV BED 10 min ≥110 Gy (HR=0.47, 95% CI 0.26 -0.84, p=0.01) and NPT ≥2 (HR=2.23, 95% CI 1.21 -4.11, p=0.01). TPC rate in univariate analysis was only significantly associated with local recurrence after SABR (HR=2.17, 95% CI 1.26-3.75, p=0.008). No parameter based on PTV was significant in both cohorts.