Natural history and prevention of radiation injury.

Radiation therapy for cancers of the head and neck can irreversibly damage the salivary glands. Xerostomia (subjective oral dryness) develops within the first week of therapy and is progressive, with devastating effects on the quality of life of the individual. The xerostomia does not correlate with the degree of salivary gland hypofunction. The mechanism of tissue injury in humans is still unclear, but much progress has been made with animal models. This paper reviews the natural history of radiation damage to human salivary glands and highlights the inter-individual variations in the responses to and recovery from therapeutic radiation. The degree of salivary gland damage is correlated to the dose of radiation delivered and the volume of gland included in the field of radiation. The molecular mechanism of acute radiation damage is not fully understood; however, long-term salivary gland dysfunction is associated with both loss of gland weight and loss of acinar cells. Various strategies have been used to prevent or alleviate the problem of salivary gland hypofunction following therapeutic radiation. This paper reviews the progress made to date and the possibilities for future interventions to prevent radiation damage.