ESTRO 2025 - Abstract Book

S935

Clinical – Head & neck

ESTRO 2025

457

Digital Poster Curative proton reirradiation (re-PT) in recurrent head and neck cancers (HNC): outcomes and toxicities Seedarat Suwichanarakul 1,2 , Anussara Prayongrat 1,2 , Danita Kannarunimit 1,2 , Chakkapong Chakkabat 1,2 , Chawalit Lertbutsayanukul 1,2 , Sarin Kitpanit 1,2 1 Division of Radiation Oncology, Department of Radiology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand. 2 Her Royal Highness Princess Maha Chakri Sirindhorn Proton Center (HPHS), King Chulalongkorn Memorial Hospital, Thai Red Cross Society, Bangkok, Thailand

Purpose/Objective: To evaluate oncologic outcomes and toxicities in patients who received re-PT with curative intent for HNC.

Material/Methods: This retrospective study included patients with recurrent, persistent, and second primary HNC who received curative re-PT at Her Royal Highness Princess Maha Chakri Sirindhorn Proton Center (HPSP) from 2022 to 2024. Patients’ clinical, treatment characteristics were reviewed and toxicities were assessed according to CTCAE version 5.0. Outcomes including locoregional control (LRC), progression-free survival (PFS) and overall survival (OS) were estimated using the Kaplan-Meier method. Results: A total of 23 patients with recurrent (70%), persistent (8%), and second primary (22%) HNC were treated with pencil beam scanning (PBS) proton therapy. The median (IQR) follow-up was 10.6 months (6.0–19.3) for all patients and 14.0 months (10.4–23.1) for living patients. The median (IQR) interval between radiation courses was 3.2 years (0.8– 8.4) with 3 patients (13%) underwent a third course of radiation. Treatment regimens included stereotactic body proton therapy (SBPT) in 10 patients (43.5%), using a typical schedule of 35 Gy in 5 fractions every other day, moderate hypofractionation in 6 patients (26.1%), and conventional fractionation in 7 patients (30.4%) with a median (IQR) equivalent dose in 2-Gy fractions (EQD2) of 49.6 Gy (43.5–60.0), 54.8 Gy (47.0–63.2) and 70.0 Gy (60.0– 70.7), respectively. In the conventional fractionation cohort, 6 patients (85.7%) received concurrent systemic therapy. Patients treated with SBPT had relatively smaller tumor volumes with median GTV of 10.9 cm 3 compared to those treated with moderate hypofractionation (45.8 cm 3 ), or conventional fractionation (45.6 cm 3 ). Overall, the 1 year LRC, PFS, and OS rates were 63.8% (95% CI, 38.3–81.0%), 47.7% (25.8–66.8%), and 69.9% (44.7–85.3%), respectively. Subgroup analysis showed a trend toward improved outcomes in patients treated with non conventional fractionation compared to those receiving conventional fractionation, with 1-year LRC of 72.0% vs. 40.0% (p = 0.105) and 1-year OS of 74.0% vs. 53.3% (p = 0.432), though not statistically significant. Grade 3 or higher acute and late toxicities were observed in 30.4% of patients. Notably, 1 patient (4%) developed grade 5 toxicity due to a left carotid blowout at 5 months following reirradiation.