Assessment of Radiation Dose and Volume Changes in the Masticatory Apparatus and their Clinical Correlation with Trismus in Oral Cavity Cancer Patients

Khan, Maham; Khan, Laraib; Ali, Tooba; Hina, Mariam; Shakeel, Fabiha; Tariq, Maria; Hafiz, Asim; Ali, Nasir; Abbasi, Ahmed Nadeem; Qureshi, Bilal Mazhar

doi:10.31557/APJCP.2026.27.10.3785

Assessment of Radiation Dose and Volume Changes in the Masticatory Apparatus and their Clinical Correlation with Trismus in Oral Cavity Cancer Patients

Document Type : Research Articles

Authors

Department of Radiation Oncology, Aga Khan University Hospital, Karachi, Pakistan.

10.31557/APJCP.2026.27.10.3785

Abstract

Objective: To investigate the radiation dose–volume effects on the masticatory apparatus and determine their correlation with trismus severity and muscle atrophy in patients with oral cavity squamous cell carcinoma (OSCC). Methods: This prospective observational study was conducted at a tertiary care oncology center, involving 30 patients undergoing adjuvant external beam radiotherapy for OSCC. Trismus was assessed using the maximal incisor distance (MID) at baseline and three months post-radiotherapy. The masseter, medial and lateral pterygoid, and temporalis muscles were contoured on planning and follow-up CT scans, and muscle volumes were calculated. Mean radiation doses were extracted from dose–volume histograms (DVHs). Statistical analyses, including paired t-tests and Pearson’s correlation, were performed to evaluate the relationships between dose, volume loss, and functional decline. Results: Post-radiotherapy, a significant reduction in MID was observed (p = 0.001), and all patients demonstrated either persistence or progression of trismus. Significant volume loss occurred in all ipsilateral muscles (p < 0.001), particularly the temporalis (mean loss, 3.32 cm³) and masseter (mean loss, 2.49 cm³). Radiation dose significantly correlated with volume reduction in the ipsilateral masseter (r = 0.511, p = 0.004) and pterygoids (r = 0.448, p = 0.013). Furthermore, worsening trismus was strongly associated with volume loss in the ipsilateral masseter (r = −0.464, p = 0.010) and temporalis (r = −0.533, p = 0.002). Age > 50 years and buccal mucosa primary sites were identified as significant clinical predictors of severe trismus. Conclusion: Radiation-induced trismus is driven by dose-dependent atrophy of the masticatory muscles, specifically the ipsilateral masseter and temporalis. Consideration of radiation dose to the masticatory muscles during treatment planning may be important for minimizing functional morbidity.

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