ESTRO 2025 - Abstract Book

S1402

Clinical - Lung

ESTRO 2025

3623

Mini-Oral Dose-response analysis of esophageal dose surface maps for patients with small-cell lung cancer treated with twice-daily radiotherapy Hild M Bekkevoll 1 , Nina Levin 2,3 , Kathrine R Redalen 1 , Bjørn Henning Grønberg 2,3 , Signe Danielsen 2,3,1 1 Department of Physics, Norwegian University of Science and Technology, Trondheim, Norway. 2 Department of Clinical and Molecular Medicine, Norwegian University of Science and Technology, Trondheim, Norway. 3 Department of Oncology, St. Olavs Hospital, Trondheim, Norway Purpose/Objective: For patients with limited-stage small-cell lung cancer (LS-SCLC), the most effective treatment is considered to be twice-daily radiotherapy (RT) with concurrent chemotherapy. Acute esophagitis is a common side effect in this RT regimen. A recent randomized phase 2 trial (NCT02041845) reported improved survival for patients with LS-SCLC treated with 60 Gy in 40 fractions, compared to the standard treatment of 45 Gy in 30 fractions. Although the dose escalation resulted in higher maximum doses to the esophagus, no increase in severe acute esophagitis was observed. This study aimed to perform a 2D dose-response analysis for the patients in the mentioned trial, considering the dose distribution on the surface of the esophagus, to identify factors that might predict severe acute esophagitis. Material/Methods: Esophageal dose surface maps (DSMs) were created for all 166 patients that started RT in the trial. All DSMs were converted into the equivalent dose in 2 Gy fractions (EQD 2 ) using an α/β-ratio of 10. Acute esophagitis was graded according to CTCAE v.4. A homogeneous dose-response was assumed for the esophagus. Thus, the area with the highest dose was centered in the middle of each DSM before creation of average DSMs for each grade of esophagitis. The esophageal length irradiated and the proportion of circumference irradiated were analyzed.

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