Quantitative dose-response analysis of salivary function following radiotherapy using sequential RI-sialography.

A total of 216 99mTc-pertechnetate-sialographies, by applying stimulations by citric acid, were performed for studying radiation effects on the salivary glands in 145 patients. From a scintigram of the salivary gland, the time-activity-curves were obtained for analysis of salivary function. The shape of the time-activity-curve with respect to stimulus-response pattern was classified into four types according to the degree of radiation-induced dysfunction. We found that the acid stimulation was enhancing accumulation of the isotope into the salivary gland as well as influencing salivary discharge. A ratio (Rc) of pre- and post-stimulation counts permitted a construction of quantitative dose-response curves; the curve for the parotids had a slight rise of Rc's over 0-20 Gy, whereas that for the submandibular glands had a significant rise over 10-30 Gy; in both glands the rise of Rc's was followed by a steep fall. The parotids appeared to be more sensitive to radiation than the submandibular glands at 0-3 months following 20-70 Gy, but after 3 months both glands were similarly impaired. The gland volume irradiated was also of great importance in determining the degree of salivary dysfunction. The maximum uptakes averaged per unit area (salivary-to-background ratio) and determined during the initial 30 minutes were greater in the submandibular than in the parotid glands following greater than 20 Gy. In both glands the maximum uptakes were gradually impaired with time over 3-36 months following 50-70 Gy.