ESTRO 2025 - Abstract Book

S1839

Clinical – Upper GI

ESTRO 2025

References: 1. iang, J.; Diaz, D.A.; Nuguru, S.P.; Mittra, A.; Manne, A. Stereotactic Body Radiation Therapy (SBRT) Plus Immune Checkpoint Inhibitors (ICI) in Hepatocellular Carcinoma and Cholangiocarcinoma. Cancers 2023 , 15 , 50. https://doi.org/10.3390/cancers15010050. 2. Bisello S, Camilletti AC, Bertini F, Buwenge M, Arcelli A, Macchia G, Deodato F, Cilla S, Mattiucci G, Autorino R, Autorino R, et al: Stereotactic radiotherapy in intrahepatic cholangiocarcinoma: A systematic review. Mol Clin Oncol 15: 152, 2021.

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Digital Poster Safe dose constraints for stomach and duodenum with carbon-ion radiotherapy Hirokazu Makishima 1 , Hirotoshi Takiyama 1 , Takashi Kaneko 2,1 , Masaru Wakatsuki 1 , Tetsuro Isozaki 1 , Hiroki Kurosaki 1 , Makoto Shinoto 1 , Hitoshi Ishikawa 1 1 QST Hospital, National Institutes for Quantum Science and Technology, Chiba, Japan. 2 Div. of radiation oncology, Yamagata University, Yamagata, Japan Purpose/Objective: Carbon-ion radiotherapy (C-ion RT) can achieve a dose distribution that minimizes exposure to nearby organs-at risk (OARs). However, OARs adjacent to the target may still receive doses close to the prescribed level. Although dose constraints for stereotactic body radiotherapy are increasingly reported, their applicability to C-ion RT remains uncertain due to differences in dose distribution and radiobiological effects. This study aims to determine the maximum tolerable dose of C-ion RT for the stomach and duodenum. Material/Methods: We extracted cases of liver tumours treated with C-ion RT at our facility between January 2016 and December 2020 from an all-case database. We then retrospectively analysed all cases receiving 60 Gy (relative biological effectiveness weighted dose) in four fractions and had gastrointestinal (GI) structures within 10 mm of the target. Dose distribution data were collected, along with periodic upper GI endoscopy results conducted every 3 to 6 months. Cases were categorized by GI tract D2cm³ dose levels and analysed for the incidence, severity (using the Sakita classification), and timing of ulcerations. Results: Among the 144 cases treated, 27 had GI tract within 10mm from the target. Nine cases developed ulcerations in regions consistent with dose distribution predictions: 3 out of 3 cases with D2cm³ ≥ 34 Gy, 6 out of 15 for 30 Gy ≤ D2cm³ < 34 Gy, and 0 out of 9 for D2cm³ < 30 Gy. A significant correlation was observed between dose level and ulceration onset, with higher doses associated with earlier onset (correlation coefficient: -0.726, p=0.027). However, no correlation was found between dose and maximum ulcer severity. Conclusion: Despite the limited sample size, a clear dose-response relationship was observed, with a steep dose-response curve. Given the additional uncertainties in particle therapy compared to photon therapy, and the steepness of this dose-response relationship, combined with the sharp dose roll-off of C-ion RT, the findings should be interpreted with caution. Nonetheless, to our knowledge, this is the first report establishing an estimate of the maximum tolerable dose of C-ion RT for the stomach and duodenum.

Keywords: Particle therapy, Liver tumors, toxicity