Background: The aim of this study is to develop a prediction model for radiation-induced trismus (maximal interincisal distance equal to or less than 35 mm) based on a multivariable analysis of dosimetric and clinical factors.

The maximum inter-incisal opening (MIO) of hean and neck cancer (HNC) patients who undergo radiotherapy (RT) ± concurrent chemotherapy with radical intent, will be prospectively measured prior to RT (baseline) and 6 months post-RT.

The potential risk factors (clinical and dosimetric) will be first screened by univariate analysis and then by multivariate analysis. At the end of this process, the features identified as relevant, will be used to fit a logistic regression model and calculate the probability of observed trismus during the 6-month follow-up after RT

Inclusion Criteria:

• HNC
• treatment definitive or postoperative external beam radiotherapy, either alone or in -combination with chemotherapy or cetuximab at least 6 months follow-up

Exclusion Criteria:

• primary tumor out-side the head and neck region, intracranially, or if it originated from the nasal vestibule
• patient death during RT or within the first 6 months after the start of RT, no outcome data available

patients with HNC treated consecutively with definitive or postoperative external beam radiotherapy, either alone or in combination with chemotherapy or cetuximab, between January 2017 and April 2021 at Gemelli Advanced Radiation Therapy (ART) center, Fondazione Policlinico Universitario Agostino Gemelli IRCCS