Pre-Irradiation Qualities of a Parotid Gland Predicting the Grade of Functional Disturbance by Radiotherapy

In the irradiation of head and neck tumours, often more than one of the major salivary glands and also many of the minor salivary glands are located within the therapy beams. This might then explain any functional disturbance of the salivary gland tissue causing xerostomia with difficulties in swallowing, a high incidence of caries, etc., after radiotherapy in this region. As the grade of these complications shows a great interindividual variation, it is questioned whether there is an individual sensitivity to irradiation therapy of the salivary gland tissue. To ascertain whether it is possible to predict in which patients radiotherapy will be more liable to cause a functional disturbance, a study has been made of 15 parotid glands located within the therapy beams at radiotherapy of malignant head and neck tumours to find whether any correlation exists between the pre-irradiation quality of the glands and their reaction to irradiation at different doses. The pre-irradiation quality of the parotid glands has been studied by sialography and sialometry, and their function during the irradiation period by sialometry during stimulation of the secretion rate with 1% citric acid. The present study shows so great an interindividual variation in the decrease of the stimulated secretion rate at irradiation that it seems impossible to estimate a definite critical dose level for extinction of parotid glands. It has, however, also been shown that the pre-irradiation qualities of the parotid glands provide valuable information about the individual reaction of the parotid glands to irradiation. These findings are important for determining the risk of complications in the mouth and throat by radiotherapy of malignant tumours in the head and neck region.