Scintigraphic assessment of salivary function and excretion response in radiation-induced injury of the major salivary glands.

Abstract

Both loss of the secretory function and impairment of the excretion may play a role in radiation-induced injury of the major salivary glands after radiotherapy for head and neck malignancies. Therefore, quantitative 99mTc-pertechnetate (99mTc) salivary scintigraphy to assess trapping, secretion, and excretion, was used to analyze irradiation-induced changes in relation to the radiation dose and the time interval after radiotherapy. Salivary scintigraphy was performed on 25 patients who had been irradiated to the neck and head for various malignancies with irradiation of the major salivary glands and in 6 nonirradiated patients. Excretion was induced by stimulation with carbachol (Carbacholum, Pharmachemie BV, Haarlem, The Netherlands). As a parameter for salivary glandular trapping and secretion, the cumulative 99mTc-pertechnetate glandular uptake in the first 12 minutes was used. Scintigraphic data were analyzed for each patient and for each individual gland at three radiation dose levels (range, 5-70 Gy), and at short (range, 2-7 months) and long (range, 10-50 months) intervals after radiotherapy. The excretion response to the stimulant carbachol was totally or partially disturbed in 84% of the irradiated patients. For individual glands, excretion was maintained in all glands irradiated with 25 Gy or less, in nearly half of the glands at doses of 25-45 Gy, and was almost invariably impaired at doses higher than 45 Gy, regardless of the time interval after radiotherapy. Although cumulative 99mTc glandular uptake tended to decrease at higher radiation dose levels (z = -3.059, P < 0.0022), at 45 Gy or more, cumulative 99mTc uptake was considerably higher in glands examined at a short postirradiation interval compared with glands examined after a long time interval (P = 0.0001). This tendency, seen for both parotid and submandibular glands, was not observed at doses lower than 45 Gy. These data suggest that in the first period after high dose irradiation, xerostomia is based predominantly on the failure of the gland to excrete saliva, whereas in the later period, a decreased trapping ability together with loss of secretory function play an additional role. Salivary scintigraphy using 99mTc-pertechnetate is a suitable method to assess radiation-induced salivary gland injury. The test is able to detect salivary glandular dysfunction in an early phase and may be useful to predict which patients will respond symptomatically to salivary stimulants.