Intensity-modulated radiation therapy for head and neck cancer.

In head and neck cancer, intensity-modulated radiation therapy (IMRT) makes the use of electron beams for irradiation of the posterior neck obsolete, inherently performs missing tissue compensation, and allows concave and intentionally nonhomogeneous dose distributions. By clinical use of these physical characteristics, salivary or lacrimal glands, optic pathway and auditory structures can be selectively underdosed and good evidence of decreased radiation toxicity is available. Evidence for increased local control is still lacking. Recurrences are mainly located in the high-dose-prescription regions, suggesting the need for even higher doses in these areas. Image-aided design of IMRT dose distribution is an area of intense research. New positron emission tomography and magnetic resonance imaging developments might allow definition of volumes inside the tumor where treatment failure is most likely to occur. If these volumes are small, focused dose escalation of large magnitude can be attempted and the hypothesis of improved local control by IMRT can be tested.