ESTRO 2025 - Abstract Book

S957

Clinical – Head & neck

ESTRO 2025

radiotherapy (6 MV photon beam, 2.12 Gy, 25-35 fractions). The treatment plans included radiotherapy alone, concurrent chemoradiotherapy, or concurrent chemoradiotherapy with hyperthermia. Before each radiotherapy session, patients were instructed to maintain the same posture and neck angle in a consistent environment. A high precision skin measurement device was used to measure 16 skin indicators (including color, brightness, moisture content, and elasticity) in different dose regions (high-dose, junction, and low-dose areas) for each fraction of radiotherapy. Photos of the treated neck skin area were taken with the same equipment, and subjective grading of acute skin reactions was evaluated using the RTOG scale for each fraction. The Pinnacle planning system was used to calculate the dose distribution on the skin at different depths, with the real surface dose determined by fitting an exponential function to the dose distribution. Additionally, individual characteristics such as age, gender, treatment plan, and tumor target area distance from the neck skin were recorded, providing nearly 2000 paired sample data points. R language was used to analyze the dose-response relationship of acute skin reactions in the neck region. Results: Six indicators (moisture content, brightness, melanin, skin color ITA, color difference ΔRGB and ΔLab) exhibited significant dose-response relationships (R > 0.8) in the high-dose region of the neck. Specifically, as the number of fractions and dose increased, moisture content, brightness, and ITA significantly decreased, while melanin, ΔRGB, and ΔLab significantly increased. In the junction and low-dose regions, the correlation was not significant. Notably, in young and middle-aged patients receiving radiotherapy alone, melanin deposition in the high-dose region of the neck was significantly and linearly correlated with the skin surface dose (slope = 0.04, R² = 0.87). Moreover, in the high-dose region, the skin objective indicators (melanin, ΔRGB, and ΔLab) showed a strong positive correlation with RTOG grading (R > 0.9). Conclusion: Skin indicators such as melanin, moisture content, and color difference can replace the current RTOG grading for the fine quantification of radiation dermatitis. By utilizing dose data, the occurrence time and severity of radiation dermatitis can be accurately predicted. Proffered Paper HYpofractionated, Dose-redistributed RAdiotherapy (HYDRA) for head and neck cancer: dosimetric comparison and planned interim analysis results Pascal A. Gunsch 1 , Reno Debets 2 , Stijn Keereweer 3 , Esther van Meerten 4 , Jaap Zindler 5,6 , Erik van Werkhoven 1 , Mischa Hoogeman 1,6 , Gerda M. Verduijn 1 , Michiel Kroesen 1,6 , Remi A. Nout 1 , Joris B.W. Elbers 1,6 1 Department of Radiotherapy, Erasmus MC Cancer Institute, Rotterdam, Netherlands. 2 Department of Medical Oncology, Laboratory of Tumor Immunology, Erasmus MC Cancer Institute, Rotterdam, Netherlands. 3 Department of Otorhinolaryngology, Head and Neck Surgery, Erasmus MC Cancer Institute, Rotterdam, Netherlands. 4 Department of Medical Oncology, Erasmus MC Cancer Institute, Rotterdam, Netherlands. 5 Department of Radiotherapy, Haaglanden Medical Center, The Hague, Netherlands. 6 Department of Radiotherapy, HollandPTC, Delft, Netherlands Purpose/Objective: Radiotherapy is the standard of care for most squamous cell carcinomas of the oropharynx, hypopharynx and larynx. However, it results in a significant treatment burden and frequently causes radiation-induced lymphopenia (RIL), which is associated with unfavorable outcomes. We hypothesize that treatment burden and RIL can be reduced by using fewer fractions (HYpofractionation), a focal boost to the tumor center and a lower elective dose (Dose-redistribution), and RAdiotherapy with protons instead of photons (HYDRA). Keywords: Radiation Dermatitis, Dose-Response 1170