[Normal tissue tolerance to external beam radiation therapy: salivary glands]

Xerostomia is one of the most a common complication of radiotherapy for head and neck cancers, affecting quality of life. Parotid glands produce approximately 60% of saliva and submandibular glands 20% of saliva while the rest is secreted by sublingual and accessory salivary glands. Methods of measuring the salivary output are collection of unstimulated or stimulated saliva or 99mTc-pertechnate scintigraphy. Several studies demonstrated that late salivary dysfunction after radiotherapy has been correlated to the mean parotid gland dose, with recovery occurring with time. Severe xerostomia could be avoided if at one parotid gland is spared to a mean dose of less than approximately 25-30 Gy. Clinical benefit of submandibular gland sparing is more controversial. A mean dose less than 39 Gy could preserve submandibular gland function. This paper aims to review main studies evaluating tolerance dose of salivary glands.