Background: The aim was to retrospectively investigate trismus (reduced mandible mobility) development in specified head and neck (HandN) cancer diagnosis according to different radiotherapy dosage regimens.
Material/Methods: Sixty-nine out of 246 patients with different HandN cancer diagnoses and available maximum interincisal opening (MIO) measurements before and after treatment were analyzed according to age, gender, radiation dose, tumor site and stage, and Karnofsky Performance Status Scale index. MIO was measured over time (range: 3–48 months), with a cutoff criterion for trismus of 35 mm.
Results: Overall, 42% of the patients had post-treatment MIO <35 mm, and trismus incidence was highest in patients treated for parotid gland tumors followed by those treated for nasopharyngeal cancers. The mean MIO values at baseline were significantly different (p=0.0078) between patients who developed trismus (i.e. MIO <35 mm; mean: 43 mm) and those who did not (mean: 51 mm). The trismus patients also had significantly larger tumors (p=0.0437), poorer physical function before start of treatment (p=0.0344), and had more often received a higher total tumor radiation dose (p=0.0418).
Conclusions: This study reports a high incidence of trismus in HandN cancer patients after treatment. Furthermore, it was found that poor physical function before the start of treatment and high external beam radiation therapy (EBRT) dosages (>50 Gy) were related to significantly more trismus. Future prospective studies are needed to provide a better understanding of different risk factors associated with trismus development, the impact on health-related quality of life, and the effects of early treatment.

Keywords: Radiotherapy Dosage, Radiation Oncology - methods, Radiation Injuries, Incidence, Head and Neck Neoplasms - pathology, Aged, 80 and over, Risk Factors, Sweden, Trismus - etiology