SCINTIGRAPHIC ASSESSMENT OF SALIVARY FUNCTION AND EXCRETION RESPONSE IN RADIATION-INDUCED INJURY OF THE MAJOR SALIVARY-GLANDS

Background. Both loss of the secretory function and impairment of the excretion may play a role in radiation-induced injury of the major sal ivary glands after radiotherapy for head and neck malignancies. Theref ore, quantitative Tc-99m-pertechnetate (Tc-99m) salivary scintigraphy to assess trapping, secretion, and excretion, was used to analyze irra diation-induced changes in relation to the radiation dose and the time interval after radiotherapy. Patients and Methods. Salivary scintigra phy was performed on 25 patients who had been irradiated to the neck a nd head for various malignancies with irradiation of the major salivar y glands and in 6 nonirradiated patients. Excretion was induced by sti mulation with carbachol (Carbacholum, Pharmachemie BV, Haarlem, The Ne therlands). As a parameter for salivary glandular trapping and secreti on, the cumulative Tc-99m-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 mont hs) intervals after radiotherapy. Results. The excretion response to t he stimulant carbachol was totally or partially disturbed in 84% of th e irradiated patients. For individual glands, excretion was maintained in all glands irradiated with 25 Gy or less, in nearly half of the gl ands 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 Tc-99m glandular uptake tended to decrease at hi gher radiation dose levels (z = -3.059, P < 0.0022), at 45 Gy or more, cumulative Tc-99m uptake was considerably higher in glands examined a t a short postirradiation interval compared with glands examined after a long time interval (P = 0.0001). This tendency, seen for both parot id and submandibular glands, was not observed at doses lower than 45 G y. Conclusion. 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 addi tional role. Salivary scintigraphy using Tc-99m-pertechnetate is a sui table method to assess radiation-induced salivary gland injury. The te st is able to detect salivary glandular dysfunction in an early phase and may be useful to predict which patients will respond symptomatical ly to salivary stimulants.