Published: May 2003
Radiation therapy is associated with a variety of side effects that vary according to total dosage, rate of radiation delivery, fraction size, field of radiation, radiation source, previous surgical intervention and individual patient status. Patients receive radiation therapy to the oral cavity and/or salivary glands for the treatment of tumors in the oral cavity, oropharynx, nasopharynx, larynx and salivary glands, and for the treatment of lymphomas and leukemias. Patients may undergo radiation therapy for 3-7 weeks with a total dose ranging from 3,000 to >7,000 centigray (cGy), depending on tumor type and location. Hodgkin's and non-Hodgkin's lymphomas require less radiation than other solid tumors of the head and neck.
Alteration and loss of taste may begin with the first 200-400 cGy. After three weeks of therapy, it takes 500-8,000 times normal concentrations of taste stimulant to elicit a normal taste response. Taste acuity levels usually return to normal 2-4 months following completion of therapy, if adequate saliva is available.
Salivary gland acini within the field of radiation may be permanently destroyed during therapy. Saliva is reduced in volume and altered in consistency. Reduction is dependent upon the total dose of radiation, degree of salivary gland involvement in the field of radiation, and individual patient variables. Flow may be reduced 50% by the end of the first week, and further reduction in volume (up to 100%) may occur. The saliva produced is more mucinous and acidic, and it may distribute less easily throughout the mouth. Salivary gland tissue does not recover from radiation damage, although some patients may perceive an improvement in salivary output over time.
The mucosa becomes edematous, erythematous, pseudomembranous, and sometimes ulcerated. Pain varies considerably in severity and may be intensified by certain foods. The patient may develop problems in swallowing and speaking. Mucositis usually occurs after the second week of radiation therapy. The lips, buccal mucosa, soft palate, borders of tongue and floor of mouth are at greater risk of mucositis. Severe symptoms usually resolve within six weeks following completion of therapy.
Secondary infections are common. While candidiasis is most common, all bacterial, mycotic and viral organisms may cause infections.
Eating difficulty caused by xerostomia, mucositis and dysphagia may lead to nutritional compromise and dehydration.
Dental Demineralization/"Radiation Caries"
Rapid demineralization and breakdown of tooth structure may occur following radiation therapy. The process may be recognized early after treatment. The teeth need not be in the direct field of radiation therapy. Demineralization results when the parotid and/or submandibular/sublingual glands are included in the field of radiation. A diminished supply of saliva, particularly of resting flow from the submandibular/sublingual glands, deprives the oral cavity of the protective components of saliva and the tooth structure of the calcium and phosphate ions necessary to maintain the hydroxyapatite content of enamel and dentin. Although some patients do not clinically appear to be xerostomic after radiation therapy, they may experience a change in the quality of their saliva, leading to rapid dental demineralization. Even a 25% decrease in saliva may result in dental breakdown.
Spasms and/or fibrosis of the muscles of mastication and temporomandibular joint may develop when the muscles and/or TMJ are in the field of radiation. This may impair saliva circulation and interfere with oral hygiene procedures and dietary intake.
Soft tissue necrosis/Osteoradionecrosis (ORN)
Soft tissue and bone necrosis may develop because tissues within the field of radiation become hypovascular, hypoxic and hypocellular. This process may be spontaneous or result from trauma, leading to non-healing soft tissue and bone lesions, and necrosis. Trauma may result from tooth extraction, invasive periodontal procedures and intraoral prosthetic appliances. The mandible is much more susceptible to ORN than the maxilla. The non-healing bone may become secondarily infected.
Developmental Maxillofacial Deformity
Children who receive radiation therapy to facial bones and developing dental structures may experience altered craniofacial growth and tooth development. The degree of deformity depends on the dose of radiation therapy and the age of the child at the time of therapy.
Long-Term Effects of Radiation Therapy
Although patients receiving radiation therapy will experience dramatic resolution of the acute effects following the completion of treatment, the long-term effects are progressive and significant. Fibrosis of tissues and hyalinization of blood vessels contribute to decreased perfusion of tissues that intensifies with time.