Xerostomia is defined as a disorder characterised by reduced salivary flow in the oral cavity (hyposalivation), and is a common side effect of radiotherapy treatment to the salivary glands. Radiation induced hyposalivation is reported as the most common long-term complication of radiation therapy for head and neck cancer.r Xerostomia has late effects on oral health, causing a dry mouth, sore throat, impaired chewing and swallowing function, altered taste, dental decay and changes in voice quality, which can negatively affect quality of life.
Saliva plays a critical role in the maintenance of oral and dental health. 90% of saliva is produced by the major salivary glands: the parotid, the submandibular and sublingual glands. Approximately 10% of saliva is produced by minor salivary glands in the oral mucosa.r
Saliva plays an important role in:
- moistening food
- physically cleansing the oral cavity
- protecting oral tissues
- assisting with the demineralisation and re-mineralisation of teeth
- reducing the adhesion of microorganisms to teeth
- helping to neutralise dietary acids.
Patients who receive radiation therapy to the head and neck are 6 times more likely to develop salivary hypofunction and xerostomia than the general population.r
Important predictors of xerostomia include the:
- radiation dose
- technique of radiation therapy
- initial volume and function of the salivary gland.
Radiation induced xerostomia starts early during treatment, with salivary flow decreasing by 50-60% in the first week of radiation therapy, and by 80% by week 7 of radiation therapy.r
Salivary function continues to decline for 6-8 months after radiation therapy and many patients show no recovery of function even 12 months later. It can develop into an irreversible life-long problem.
Risk factors for radiation induced xerostomia include:
- radiation therapy to the salivary glands
- radiation dose* and technique
- concomitant chemotherapy
- use of radioprotectors
* The dose of radiation is correlated with xerostomia. There is temporary loss of saliva after exposure of 10Gy being delivered to the salivary glands. The delivery of 40-50Gy causes permanent loss of salivary function.