Partial irradiation of the parotid gland

Recent efforts to reduce xerostomia associated with irradiation (RT) of head and neck cancer include the use of conformal and intensity-modulated RT (IMRT) to partly spare the major salivary glands, notably the parotid glands, from a high radiation dose while treating adequately all the targets at risk of disease. Knowledge of the dose-volume-response relationships in the salivary glands would determine treatment planning goals and facilitate optimization of the RT plans. Recent prospective studies of salivary flows following inhomogeneous irradiation of the parotid glands have utilized dose-volume histograms (DVHs) and various models to assess these relationships. These studies found that the mean dose to the gland is correlated with the reduction of the salivary output. This is consistent with a pure parallel architecture of the functional subunits (FSUs) of the salivary glands. The range of the mean doses, which have been found in these studies to cause significant salivary flow reduction is 26 to 39 Gy.