Chemoradiation to the Submental Muscles Alters Hyoid Movement During Swallowing in a Rat Model

Hyolaryngeal dysfunction is a commonly reported swallowing problem after chemoradiation treatment for head and neck cancer. The displacement of the hyolaryngeal complex during swallowing protects the airway and assists in opening the upper esophageal sphincter. Activation of the submental muscles, specifically the mylohyoid and geniohyoid muscles, are thought to facilitate movement of the hyoid. The purpose of this study was to determine if targeted radiation to the submental muscles given concurrently with chemotherapy alters hyolaryngeal displacement one-month after treatment. We hypothesized that chemoradiation treatment will result in abnormal patterns of hyoid movement compared to controls. Furthermore, we propose that these changes are associated with alterations in bolus size and discoordination of the jaw during drinking. Eighteen rats underwent either chemoradiation, radiation, or no treatment. Radiation treatment was targeted to submental muscles using a clinical linear accelerator given in 12 fractions of 4Gy (3 days per week). Cycles of 1mg/kg of cisplatin were administered concurrently each week of radiation. One-month post-treatment, videofluoroscopy swallow studies (VFSS) were performed in self-drinking rats using a fluoroscope customized with a high speed camera. The hyoid, jaw, and hard palate were tracked during swallowing from VFSS. Hyoid kinematics were analyzed from the start to the end of hyoid movement, and parameters were compared to bolus size and jaw movement. Significant differences in hyoid retraction parameters were found post chemoradiation. Alterations in the trajectory of hyoid motion during swallowing were observed. Findings demonstrate early changes in hyoid motion during swallowing associated with chemoradiation treatment.