Late oral complications of radiation therapy are chiefly a result of chronic injury to vasculature, salivary glands, mucosa, connective tissue, and bone.[1,2,3,4] The types and severity of these changes are directly related to radiation dosimetry, including total dose, fraction size, and duration of treatment.
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Mucosal lesions include epithelial atrophy, reduced vascularization, and submucosal fibrosis. These changes lead to an atrophic, friable barrier. Fibrosis involving muscle, dermis, and the temporomandibular joint results in compromised oral function. Salivary tissue changes include loss of acinar cells, alteration in duct epithelium, fibrosis, and fatty degeneration. Compromised vascularization and remodeling capacity of bone leads to risk of osteonecrosis.
Salivary Gland Hypofunction and Xerostomia
Ionizing radiation to salivary glands results in inflammatory and degenerative effects on salivary gland parenchyma, especially serous acinar cells. The early salivary gland tissue response to irradiation results in decreased salivary flow rates within the first week of treatment, and xerostomia (the subjective feeling of oral dryness) becomes apparent when doses exceed 10 Gy.
The degree of dysfunction is related to the radiation dose and volume of glandular tissue in the radiation field. Doses larger than 54 Gy are generally considered to induce irreversible dysfunction. Serous parotid glands may be more susceptible to radiation effects than are nonserous submandibular, sublingual, and minor salivary gland tissues. Management strategies described for late salivary gland complications are generally applicable to the acute complications in the head/neck radiation patient. (Refer to the Oral and dental management of the xerostomic patient section of this summary for more information.)
Salivary gland hypofunction (decreased salivary gland secretion) and xerostomia are among the most frequent and severe long-term side effects of radiation therapy to the head and neck region. The adverse effects will have a significant impact on a patient's quality of life in a lifelong perspective after radiation treatment.
Xerostomia is caused by salivary gland hypofunction. Saliva is necessary for the normal execution of oral functions such as taste, swallowing, and speech. Unstimulated whole salivary flow rates lower than 0.1 mL per minute are considered pathologic low (normal salivary flow rate = 0.3-0.5 mL/min).
Late salivary tissue changes induced by radiation therapy include loss of acinar cells, alteration in duct epithelium, fibrosis, and fatty degeneration. The early response to irradiation resulting in markedly decreased salivary flow rates within the first week of treatment is followed by a further decline in saliva secretion and worsening of xerostomia after radiation therapy (1-3 months posttreatment), whereafter salivary secretion and xerostomia gradually recover over time (maximum recovery, 1-2 years posttherapy), depending on the total radiation dose to the gland tissue. Recovery of salivary gland function is usually incomplete, and the overall degree of dryness can range from mild to severe.