Quantification of salivary gland function in thyroid cancer patients treated with radioiodine

Damage to salivary gland function following external irradiation has been documented. However, the extent of damage following radioiodine (131I) therapy for thyroid cancer has not been adequately studied. We evaluated salivary dysfunction in Ca-thyroid patients treated with therapeutic doses of 131I.

A simple acquisition and analysis protocol using 99mTcO4- (pertechnatate) and a gamma camera computer system was planned. The uptake of 99mTcO4- by the salivary glands at 10 min and percent of excretion of 99mTcO4- from the glands in response to a sialogogue (lemon juice) was studied in 33 patients treated with 1.369-38.702 GBq of 131I (Mean = 10.16 GBq, standard deviation = 7.659 GBq) in addition to 14 athyreotic controls.

Significant damage to the salivary gland in terms of abnormal percent uptake or excretion was noted in 72.73% of the patients. Forty-eight percent of the patients treated with 131I showed asymmetrical involvement of the salivary complexes as opposed to none of the controls. Reduction in uptake of 99mTc4- or response to sialogogue was dose dependent, being more marked with higher radioiodine doses. Parotid glands were more affected than submandibular glands following 131I therapy.

131I therapy produces a significant effect on salivary gland function that is dose related and becomes evident over a period of several months after treatment.