ESTRO 2025 - Abstract Book

S1228

Clinical – Lower GI

ESTRO 2025

1 Radiation Oncology, Azienda Ospedaliera Universitaria Integrata, Verona, Italy. 2 Medical Physics Unit, Azienda Ospedaliera Universitaria Integrata, Verona, Italy. 3 Oncology Unit, Azienda Ospedaliera Universitaria Integrata, Verona, Italy Purpose/Objective: SBRT in Metastatic Colorectal Cancer: Managing Oligoprogressive or Oligopersistent Lesions and Shifting Systemic Therapy – Single-Center Analysis. Material/Methods: A retrospective single-center analysis was conducted on mCRC patients treated with systemic therapy who underwent SBRT for oligopersistent/oligoprogressive lesions. The time to next-chemotherapy (TTNLC) was defined from SBRT to the subsequent chemotherapy-line. Local control (LC) and progression-free survival (PFS) were measured from SBRT to local progression and to any progression, respectively, at the last follow-up.Overall survival (OS) was calculated from metastasis diagnosis to death or last follow-up. Statistical analysis was performed using the Kaplan-Meier method in RStudio. Subgroup analysis was performed based on SBRT timing relative to chemotherapy, with three subgroups: Group1 (SBRT followed by first-line), Group2 (first-line-SBRT-second-line), and Group3 (second-line-SBRT-third-line). Results: Eighty-four patients (median age 65, range 28-83) received SBRT: 20 oligopersistent (23.8%) and 64 oligoprogressive disease (76.2%). 122 metastatic lesions were treated from December 2016 to May 2023, primarily in the lungs (53.6%), liver (28.6%), lymph nodes (11.9%), and other sites (6%). The median dose was 50 Gy (range 24-75). 58.3% of patients received 5 fractions. The median biological effective dose (BED) was 100 Gy 10 (range 37.5-262.5). With a median follow-up of 56 months (range 10-1670), SBRT delayed systemic therapy in 38 patients (45.2%). The median TTNLC was 17.91 months (range11.8-27.43). The median TTNLC for Group1, Group2, and Group3 were 10.1 ( range 3.2-48.1), 9.4 (range 2.03-49.7), and 9.73 (range 4.3-32.4) months, respectively.The number of lesions treated (single vs. multiple) had no impact on TTNLC (p=0.4). Local progression occurred in 37 patients (44%), with a median LC of 8 (range 1.3-54.6) months.Patients with lung metastases had better LC and TTNLC (p=0.006). Additionally, patients treated with a BED ≥100 Gy 10 experienced improved LC and delayed TTNLC (p=0.002). Disease progression occurred in 63 patients (75%), with a median PFS of 5.5 (range 1.1-54.6) months . PFS was better in Group 1 (p=0.01).No significant differences were found between oligoprogressive and oligopersistent disease for any endpoint.Figure 1 summarized the Kaplan-Meier estimates for each endpoint.