Scintigraphic assessment of parotid function prior to and after radiotherapy for patients with nasopharyngeal carcinoma

Purpose:To study the parotid function with quantitative 99m Tc pertechnetate salivary scintigraphy prior to and after radiotherapy for patients with nasopharygeal carcinoma (NPC) and to analyze irradiation induced changes in relation to radiation dose, fields size and time interval after radiotherapy. Methods:From August 1995 to August 1997, 82 histologically proven NPC patients were referred to receive radical radiotherapy. 44 patients were treated with faciocervical fields (median doses: 7393 cGy/53days) and 38 patients with pre auricular fields (median doses: 7138 cGy/51days) to the primary regions. The parotid scintigraphy was performed prior to radiotherapy and at doses of 9.5Gy/5Fx or 19Gy/10Fx, at the end of radiotherapy, and every 6 months for 2 years 9.5Gy/5Fx and 19Gy/10Fx as compared to that of pretherapy, and to the lowest level at the end of radiotherapy. During the 2 years follow up period, no increase of ER and EI was observed. UR did not decrease significantly until 1 year after radiotherapy. The ER and EI of after radiotherapy. After intravenous administration of 185 MBq (5 mCi) 99m TcO - 4, sequential minute frames were acquired simutaneously. After 15 minutes, 200 mg of vitamin C were placed on the tongue to stimulate salivary excretion. Data were analyzed by computer and parameters including uptake rate (UR), excretion rate (ER) and excretion index (EI) were acquired. Results:ER and EI decreased significantly after doses of pre auricular fields were higher than those of faciocervical fields more than 1 year after radiotherapy. Conclusions:Parotid function decreased significantly after small doses of 9.5 Gy to the nasopharynx, and no increase was observed during the 2 years follow up time. It would contribute to improvement of the quality of life of the patients if the volume and dose of irradiation to the parotid were reduced.