The influence of pre-radiation salivary flow rates and radiation dose on parotid salivary gland dysfunction in patients receiving radiotherapy for head and neck cancers

Radiotherapy (RT) used for head and neck cancers causes permanent salivary gland dysfunction (SGD). Previous short-term studies have demonstrated that pre-RT salivary flow rates and the amount of radiation exposure to parotid glands influence the amount of RT-induced SGD. The purpose of this study was to determine which variables are related to the development of long-term post-RT SGD. Parotid flow rates (PFR) were assessed prior to and 1 year after completion of RT in spared parotid glands from 34 patients from 2 parotid-sparing protocols. The results reveal that spared PFR were not significantly higher 1 year post-RT in patients who had high pre-RT PFR, when compared with patients with low pre-RT PFR. However, patients who received higher doses of RT to spared parotid glands had lower PFR 1 year post-RT, compared with patients who had received lower doses of RT. These one-year findings suggest that high pre-RT PFR do not provide protection against RT-induced SGD. Conversely, reduced RT dosages to contralateral parotid glands are protective of PFR after completion of RT.