ESTRO 2025 - Abstract Book

S1230

Clinical – Lower GI

ESTRO 2025

Material/Methods: We analyzed data from patients treated with definitive RT/CRT from 2019 to 2024. Radiologic complete response (rCR) was assessed with pelvic MR at 3 months (according to RECIST v.1.0), while 6 months 18-FDG PET/CT was delivered, recordering metabolic complete response (mCR), maximum and mean Standard Uptake Value (SUVmax; SUVmean), Metabolic Tumor Volume (MTV), Total Lesion Glycolysis (TLG). Local Control (LC) was defined as time from the end of CRT to local failure or last follow-up. Univariate analysis (UVA) was performed to identify variables associated with outcome using the Log rank test. Sensitivity and Specificity analysis was performed to assess the correlation between rCR/mCR and LC. Chi square test and ROC curve analysis were performed to correlate metabolic parameters and LC. Results: A total of 67 patients (median age 67 years, range 44-83) were included. All patients completed RT, and 52 received CRT. Baseline and surveillance MR and 18-FDG PET/CT were available for 49 patients. After a median follow-up of 28 months, 12 patients experienced disease progression (PD) (10 local; 2 distant), resulting to salvage surgery in 10 cases after biopsy. At 3 years, LC rate was 78%. At UVA, only mCR was correlated with LC (3-year LC 90% vs 59%, p=0,0137; HR 0,01660, IC 95% 0,03-0,84). For prediction of LC, accuracy of mCR at 6 months was 83.7% vs 62.5% for rCR. Specificity/Sensitivity analysis is summarized in Table1. In patients with baseline and 6 months 18FDG PET/CT, at ROC curve analysis a SUVmean > 3.7 at 6 mounts 18FDG PET/CT was correlated with higher local failure (sensitivity 66,7%; specificity 97%).

Conclusion: 18FDG PET/CT at 6 months may identify patients with a higher likelihood of developing complete response following CRT. Larger series are needed to confirm this finding and identify the appropriate surveillance strategy after CRT.

Keywords: locally advanced SCC anal canal, 18-FDG PET/CT

3130

Digital Poster Pulmonary Oligometastases from Colorectal Carcinoma Treated with Stereotactic Body Radiotherapy: Experience of a Single Institution Alice Alves, Inês Sá Couto, Fátima Aires, Catarina Dias, Margarida Marques, Lígia Osório Radiotherapy service, ULS São João, Porto, Portugal Purpose/Objective: Distant dissemination is common in Colorectal Cancer (CRC), with lung being a frequent site of metastasis. Pulmonary oligometastases from CRC occur in 10%-15% of cases. Surgery is the preferred treatment for resectable disease. Stereotactic body radiation therapy (SBRT) is a safe and effective therapeutic option for selected patients. This study aims to evaluate the efficacy of SBRT and overall survival (OS) in the selected sample.