Evaluation of Major Salivary Gland Function by Sialoscintigraphy in Nasopharyngeal Carcinoma Patients Receiving Radiotherapy

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Purpose: To evaluate the major salivary gland functions by sialoscintigraphy in nasopharyngeal carcinoma patients treated by radiotherapy. Materials and Methods: This analysis includes 28 nasopharyngeal cancer (NPC) patients and 31 sialoscintigraphies. The sialoscintigraphies were grouped as pre-radiotherapy (pre-RT), low dose (＜1050 cGy), and high dose (＞1050 cGy) according to the radiation dose given to the patients when the scanning was performed. Apart from 3 patients who received 2scannings, the other 26 patients received only one test. Another 8 normal adult sialoscintigraphics were included as controls. Patients, noa-irradiated or irradiated with high or low doses, were given 10mCi(superscript 99m) Tc-pertechnetate and scanned immediately. Twenty minutes later 200 ml of lemon juice was given by month and the patient was scanned again for another 20 minutes. Time-activity curves and the cumulative gland (superscript 99m)Tc-pertechnetate uptake of each gland were plotted and calculated. The stimulated secretion is defined as: stimnlated secretion (SS)=[1-(min/max)]×100%. The downward slope was also obtained from the post-stimnlation curve of the time-activity curve to describe the secretory function. Results: A strong positive excretion response after lemon juice stimulation of both parotid and submandibular glands was noted in non-irradiated patients. After irradiation of 1050 cGy or less, a significant impairment in secretion of all major salivary glands was noted. The trapping of (superscript 99m)Tc-pertechnetate was not affected as compared with the normal controls and pre-RT scannings. After a larger dose of radiations, no curves displayed excretory response after stimulation. In terms of qualitative measurement, the 99mTc-pertechnetate uptake is not different among the four groups of patients in either parotid or submandibular glands except in the group after high dose radiations. The down slopes and stimulated secretion are statistically different between the non-irradiated and the irradiated groups. Conclusion: The salivary gland secretion was totally or partially disturbed in all patients after high dose radiation . Cumulative uptake of (superscript 99m)Tc-pertechnetate after high dose is statistically higher than pre-RT patients. Stimulated secretion was markedly retarded after high dose radiation. The data imply that the mechanism of dry mouth after high dose irradiation was mainly excretory dysfunction rather than uptake disturbance of metabolic substances. This observation is valuable in the understanding of the underlying mechanism of radiation-induced salivary gland dysfunction, and may contribute to the future resolution of this difficult side effect.