Salivary analysis in dogs undergoing definitive radiation therapy for head and neck cancer

Abstract

[EMBARGOED UNTIL 08/01/2025] Xerostomia ("dry mouth") is one of the most common side effects of radiotherapy of head and neck tumors (HNT) in people and can significantly impact a patient's quality of life post-treatment. Aside from causing dry mouth, this condition may affect chewing, swallowing, and oral health. There are numerous diagnostic tools that have been utilized to diagnose and monitor xerostomia which include assessing salivary flow rates, proteomics, questionnaires, advanced imaging with CT and/or MRI, and videofluoroscopy. There is limited literature describing the incidence of radiation-induced xerostomia on canine patients. This study seeks to characterize the effect of radiation therapy on saliva composition and production, swallowing kinetics, and the clinical impact on canine patients with HNT. Dogs undergoing definitive-intent radiation therapy for HNT were prospectively enrolled in a clinical trial. Sixteen dogs were enrolled in the study, 14 dogs had nasal tumors and two dogs had oral tumors. Patients received timed saliva collection, saliva composition analysis, video/audio recordings of free feeding, and videofluoroscopic swallow study (VFSS) before and 1-, 3-, 6-, 9-, and 12-months post-treatment. Clients were also given a questionnaire to complete at each recheck. Saliva components were assessed in nine healthy dogs to establish baseline levels of lactate dehydrogenase (LDH), calcium, amylase, and phosphorus; mean values comparable to previously published data. The control and study group were similar, aside from a significant difference in phosphorus levels. The only significant finding, when assessing the study patients' components from baseline to 6-months post treatment, was a significant increase in the phosphorus level (P=0.03). Six study dogs had their saliva collection time recorded and there was a statistically significant increase in the saliva collection time across the 12-month recheck period (P=0.019). The significantly increased saliva collection time suggests that dogs with HNT experience radiation-induced xerostomia in the post-treatment period. Standardized client questionnaires were used to assess patients' eating and drinking behaviors. Results were variable, but most patients had abnormalities noted in the post-treatment setting and the majority of these coincided with prolonged saliva collection times. Interestingly, two patients were noted to develop severe calculus and gingivitis and required a dental cleaning in the post-treatment period. The absorbed radiation dose to the zygomatic, mandibular, and parotid glands was assessed. The highest mean dose was received by the zygomatic salivary glands, most notably the ipsilateral zygomatic gland (34.72 Gy). The volume of the zygomatic glands in the pre-treatment and post-treatment CT were assessed and there was a 58 percent volume reduction of the ipsilateral zygomatic gland. These patients were noted to have prolonged saliva collection times at this 6-month recheck period. Two methods were used to assess swallowing in the patients: VFSS and standard video/audio recordings during free feeding. Two patients were included in the VFSS portion of the study and five were included in the video/audio recordings. The video/audio analysis is underway. The results from VFSS are variable. The Lick-Swallow-Rate (LSR) and Inter-Swallow-Interval (ISI) were almost doubled at either the 1-month or 3-month recheck study. The time to maximum hyolaryngeal excursion (HLE) and pharyngeal transit time (PTT) were also elevated in the post-treatment period. These findings correlated with a prolonged saliva collection time in these dogs at these timepoints. The combination of these results demonstrate that canine patients can develop radiation-induced xerostomia and this side effect may impact the patients eating and drinking behaviors and oral health. These changes may impact a patient's quality of life and strategies to limit xerostomia and manage these clinical signs should be explored.