ESTRO 2025 - Abstract Book

S987

Clinical – Head & neck

ESTRO 2025

1 Department of Oncology, Radiation Oncology, University of Turin, Turin, Italy. 2 Radiation Therapy Unit, University Hospital Center "Mother Teresa", Tirana, Albania. 3 Department of Surgical Sciences, Dental School, University of Turin, Turin, Italy Purpose/Objective: Trismus is a potential side effect for head and neck cancer (HNC) patients undergoing RT, defined as a maximum interincisal opening (MIO) ≤ 35 mm [1]. To date no consistent associations between baseline dosimetric/clinical parameters and trismus incidence in nonmetastatic HNC patients treated with definitive RT (+/- chemotherapy) have been identified. This study aims to prospectively evaluate dosimetric and clinical trismus predictors. Material/Methods: Nonmetastatic HNC patients candidate to RT (either LINAC-based or Tomotherapy, +/- chemotherapy) were prospectively enrolled in an international study. Details on pre-existing conditions of the oral cavity, masticatory muscles, temporomandibular joint and structural craniofacial features were collected at baseline. MIO measurements to assess trismus were performed through the TheraBite use at baseline, RT-end, 1, 3-, 6-, 9-, and 12-months post-RT. Trismus-related muscles (masseter, temporalis, and medial and lateral pterygoids) were contoured for the dosimetric analysis but no sparing was performed. The correlation between muscles’ metrics and changes in MIO (from pre-RT to the 6-months follow-up) was assessed using a linear regression model. Potential correlations with clinical/tumor-related factors were analyzed as well. Results: From November 2022 to August 2023, 38 patients were enrolled among two centers. Table 1 summarizes tumor and treatment characteristics. At the present analysis, MIO evaluation focused on the 74% of patients who completed a 6-months post-RT follow-up. Baseline assessments showed that 21% (8 patients) had trismus. By the end of RT, 2 of these 8 patients showed an improvement in trismus due to treatment response, which reduced tumor-related masticatory muscle infiltration. However, 13 new cases of trismus emerged post-RT. Across all follow up timepoints (1-, 3-, and 6-months post-RT), bilateral lateral pterygoids (LPs) V40Gy and V60Gy showed statistical significance (p < 0.05) as trismus predictors. Tumor site and disease laterality did not significantly impact trismus onset. Notably, patients treated with LINAC-based methods exhibited earlier trismus-related toxicity than those treated with Tomotherapy.

Conclusion: