ESTRO 2025 - Abstract Book

S1036

Clinical – Head & neck

ESTRO 2025

Conclusion: This study found a linear decreasing coverage of PTV2, a increasing dose in parotid gland, thyroid, brainstem, and spinal cord during NPC radiation, hoping to facilitating the decision-making on the structures required attention in ART and its timing.

Keywords: morphological change, dosimetric change

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Digital Poster Acute Toxicity Comparison Between IMPT and VMAT for Nasopharyngeal Cancer: A Propensity Score Matched Analysis Kiattisa Sommat, Yoke Lim Soong, Melvin Lee Kiang Chua, Joseph Tien Seng Wee, Kam Weng Fong, Terence Wee Kiat Tan, Sharon Shuxian Poh, Fu Qiang Wang, Shun Zi Liong, Wei Ren, Jing Hu, Ashley Li Kuan Ong, Sze Yarn Sin, Jacinda Geok Gun Tan, Charissa Ming-En Chu, Than Than Shwe Radiation Oncology, National Cancer Center Singapore, Singapore, Singapore Purpose/Objective: This study aimed to compare the acute toxicity profiles of Intensity Modulated Proton Beam Therapy (IMPT) and Volumetric Modulated Arc Therapy (VMAT) in patients with nasopharyngeal cancer (NPC). Material/Methods: The study included 39 NPC patients treated with IMPT between 2023-2024 and another group comprising 207 NPC patients treated with VMAT between 2019-2024 at National Cancer Center Singapore. Patients treated with IMPT were propensity score-matched at a 1:1 ratio with those treated with VMAT based on age, gender, N-stage, T-stage and treatment modality. Patients underwent prospective evaluation of physician-assessed toxicities, graded using Common Terminology Criteria for Adverse Events (CTCAE) version 4.0 at baseline, weekly during RT, 1 week, 1 month and 3 months post RT. Key endpoints included the incidence of grade 2 and worse toxicities such as oral pain, xerostomia, dysgeusia, dysphagia, pharyngolaryngeal pain and dermatitis. Weight change from baseline is assessed and compared between the two groups. Statistical comparisons of demographic and clinical characteristics as well as the acute toxicities were performed using Fisher’s Exact tests for categorical variables and Mann-Whitney U tests for continuous variables. Results: After matching, 78 patients were included in the analysis, with 39 in the IMPT group and 39 in the VMAT group. There were no significant imbalances between the 2 groups (Table 1). Most of the toxicities peaked at week 7 of RT with the IMPT group experienced significantly lower rates of Grade 2 or higher xerostomia (38.7% vs. 64.3%, p=0.037), dysgeusia (48.4% vs. 92.9%, p <0.001), dysphagia (29% vs. 57.2%, p=0.04), pharyngolaryngeal pain (6.5% vs. 35.7%, p =0.018) compared to the VMAT group (Figure 1). VMAT group experienced significantly greater weight loss compared to IMPT group from Week 3 of RT, especially at 3 months post RT (-9.8% vs. -2.2%, p = <0.001). Notably, at week 6 of RT, dermatitis was more severe in the IMPT group compared to the VMAT group (50% vs. 22.9%, p=0.018).