Head and neck cancer care, including tumors of the mouth, nose, throat and voice box, often requires radiation for cure to be achieved. Despite advances in radiation, 40% to 60% of patients experience a significant dry mouth (xerostomia) following radiotherapy. Several factors are associated with severe xerostomia including older age, advanced stage disease and tumor location. Currently, no pragmatic treatment strategy exists to reduce the risk of radiation-related xerostomia in patients with head and neck cancer. The investigators propose the use of a botulinum neurotoxin injected into the at-risk salivary glands before radiation as a strategy to preserve salivary gland function during radiation treatments and reduce xerostomia.

Inclusion Criteria:

• Newly diagnosis AJCC 8th edition Stage III/IVa mucosal head and neck squamous cell carcinoma requiring definitive radiotherapy (with or without chemotherapy).

Exclusion Criteria:

• Previous radiation to the head and neck
• Previous treatment for head and neck cancer
• Personal history of xerostomia
• Hypersensitivity to onabotulinumtoxinA
• Previous major salivary gland surgery
• Previous exposure to radioactive iodine therapy