ESTRO 2025 - Abstract Book

S1231

Clinical – Lower GI

ESTRO 2025

Material/Methods: Twenty-nine patients treated with SBRT (49 lesions) between 2016 and 2024 were included. Data were obtained from clinical records. Survival was calculated using the Kaplan-Meier method. Results: Twenty-nine patients with 49 metastatic lesions were included. The median age was 71 years, with 17 male patients (58.62%). Twenty-eight patients had an ECOG score of 0-1 (96.55%). In 34.48% (n=10) a KRAS gene mutation was present, and 93.10% (n=27) of the lesions were peripheral. The most common late toxicities (RTOG) were dyspnea and asthenia (44.82%, n=13). A complete response to treatment was observed in 6.89% (n=2). Most cases showed lesion stability (58.62%, n=17). The median follow-up period was 36 months, with an OS of 53.9% (σ=12.5%). At 60 months, there was an increase in OS with the introduction of chemotherapy (OS for patients who received chemotherapy either before and/or after SBRT was 60%, σ=15.5%). In patients with a KRAS mutation, OS at 60 months was 24.7% (σ=20.9%). For lesions larger than 25mm, OS at 60 months was lower. Conclusion: SBRT proved to be an effective treatment, demonstrating acceptable toxicity in this cohort, with a local control of 82.76% and an OS of 53.9%. The findings suggest that factors such as lesion size and KRAS mutation appear to negatively impact long-term OS; however, local control was achieved in the majority of patients. References: 1.Fu, M. X., Carvalho, C., Milan-Chhatrisha, B., & Gadi, N. (2023). Stereotactic body radiotherapy for management of pulmonary oligometastases in stage IV colorectal cancer: A perspective. Clinical Colorectal Cancer, 22 (4), 402 410. https://doi.org/10.1016/j.clcc.2023.09.001 2. Correia, D., Gonçalves, S. C., Vinagre, F., Casalta-Lopes, J., Nobre-Góis, I., & Borrego, M. (2021). Stereotactic body radiation therapy in the treatment of pulmonary oligometastatic colorectal carcinoma. Revista Portuguesa de Coloproctologia , Setembro-Dezembro 2021. Mini-Oral Radiotherapy for rectal NEC treated with surgery and chemotherapy: a population-based cohort study Xiaojun Liu, Shuping Li Division of radiation oncology, Gansu Provincial Hospital, Lanzhou, China Purpose/Objective: NECs are a highly aggressive cancer type associated with dismal prognosis and rapid disease progression. Surgical resection remains the mainstay of treatment for most localized rectal NECs, while adjuvant chemotherapy may reduce the risk of recurrence and is recommended in surgically resected patients 1] . However, the additional benefit of radiotherapy for these patients is unclear to date [2-3] . This study aims to evaluate the outcome of radiotherapy in rectal NECs who treated with surgery and chemotherapy. Material/Methods: This is a retrospective controlled study based on SEER database [4] . Propensity score matching (PSM) was applied to eliminate the baseline bias. we extracted the clinical data using data from SEER database. Patients: Rectal NECs who underwent surgical resection plus chemotherapy with or without radiotherapy were extracted from SEER database. According to whether or not receiving radiotherapy, patients were divided into two cohorts: radiation treatment (RT) Keywords: SBRT, Oligometastases, Colorectal Carcinoma 3212