ESTRO 2025 - Abstract Book

S1314

Clinical - Lung

ESTRO 2025

Keywords: radiation pneumonitis,lung cancer,4dCT

References: 1. Quantifying ventilation change due to radiation therapy using 4DCT Jacobian calculations. Taylor.J.Patton et, al Med Phys. 2018 Aug 31;45(10):4483–4492. doi: 10.1002/mp.13105

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Digital Poster Safety and Efficacy of Lattice Spatially Fractionated Radiation Therapy for Thoracic Bulky Tumor Peng Xu 1,2 , Jinyi Lang 1 , Ke Yuan 1 , Jie Yin 1 , Dongmei Liu 1 , Shun Lu 1 , Ming Fan 1 , Min Liu 1 1 radiotherapy, Sichuan Cancer Hospital & Institute, Affiliated Cancer Hospital of University of Electronic Science and Technology of China, Chengdu, China. 2 School of Medicine, University of Electronic Science and Technology of China, Chengdu, China Purpose/Objective: Lattice spatially fractionated radiation therapy (LSFRT) is currently considered as a modern approach for bulky advanced tumors, but the treatment process and safety for the treatment of thoracic bulky tumors are not yet clear. Therefore, we report the procedure and safety of LSFRT for thoracic bulky tumors at our institution. Material/Methods: Treatment of these challenging cases with LSFRT requires many considerations, including tumor localization, method for setting up peak valley areas, fractionation selection, and plan optimization. The lattice vertices inside the tumor with different spatial parameters regarding lattice layouts were automatically placed with a hexagonal close packing-based pipeline. Varied vertex radius (range:2-4mm) and center-to-center distance (range:25-55mm) were respectively optimized in the Monaco treatment planning system for each patient. All vertices should be more than 1cm away from the tumor edge. The dose for the entire tumor was 400cGy per fraction, while the vertices dose was set at 1200cGy per fraction. From December 2022 to December 2023, 9 advanced patients with thoracic bulky tumor were treated by LSFRT with a 3+3 dose escalation mode. The first 3 patients were irradiated 2 fractions, the second 3 patients were irradiated 3 fractions, and the last 3 patients were irradiated 5 fractions. Patient characteristics, planning parameters, toxic side effects, and treatment outcomes were analyzed. Results: These bulky tumors had a median volume of 848.5 cc (range, 314–2318 cc). Each patient used 15 different spatial parameters to design a plan and obtain the optimal peak to valley dose ratio (PVDR) and volume of peak dose to valley ratio (VPDVR). The median PVDR of all patients was 2.07 (range, 1.82-2.24%) and the VPDVR was 2.42 (range, 0.51-6.75). The median follow-up time was 13.4 months (range: 5.1–21.0 months). All patients showed a partial response. The median tumor regression rate within 2 months was 63.6% (range, 26.1-94.2%). No grade 3 or higher radiation toxicities were reported. 3 patients died due to tumor progression. 3 patients showed local progression after LSFRT. Conclusion: LSFRT is a well-tolerated and low risk treatment for thoracic bulky tumors and offers effective local control. A multidisciplinary approach should guide the treatment of such cases to combine with other drug treatments.

Keywords: Spatially fractionated radiation therapy, Lattice