Comparison of radiosensitivity of rat parotid and submandibular glands after different radiation schedules.

BACKGROUND AND PURPOSE: To investigate the radiosensitivity of rat parotid and submandibular gland functioning after local single dose, conventional fractionated and accelerated fractionated irradiation. METHODS: The salivary glands of male albino Wistar rats were locally irradiated with a single dose (15 Gy) or a calculated (alpha/beta; 9.6) biological effective dose of fractionated irradiation equal to this, viz. conventional fractionation (32 Gy in 16 fractions of 2 Gy/day, five times/week) or accelerated fractionation (32 Gy in 16 fractions of 2 Gy, two fractions/day). Parotid and submandibular/sublingual saliva samples were collected by means of miniaturized Lashley cups before and up to 240 days after irradiation. Salivary flow rate, lag phase and amylase secretion were used as parameters for the assessment of salivary gland function. At the end of the experiments the animals were sacrificed and the glands processed for histopathological examination. RESULTS: Up to 120 days after irradiation no differences were observed between the glands or between the different irradiation schedules. Beyond 120 days, however, the parotid gland performed better in flow rate and lag phase after fractionated irradiation, when compared to the submandibular gland. The observed differences in function corresponded with the observed late histopathological changes. The parotid gland contained more acinar cells and had a higher gland weight. No differences were observed between both fractionation schedules on each gland. CONCLUSIONS: The main observation from this study is the higher radiosensitivity of the submandibular gland compared to the parotid gland for late effects after fractionated irradiation. This may have implications for the treatment planning in case of radiotherapy for head and neck cancer.