Intensity-modulated radiation therapy in head and neck cancers: an update

Intensity-modulated radiation therapy (IMRT), an advent of three-dimensional conformal radiotherapy (3D CRT), has excited the profession of radiation oncology more than any other new invention since the introduction of the linear accelerator. Approximately 1000 articles have been published on this topic to date, more than 200 of which focus on head and neck cancer. IMRT is based on computer-optimized treatment planning and a computer-controlled treatment delivery system. The computer-driven technology generates dose distributions that sharply conform to the tumor target while minimizing the dose delivered to the surrounding normal tissues. The high dose volume that tailors to the 3D configuration of the tumor along with the ability to spare the nearby normal tissues allows the option of tumor dose escalation. The head and neck region is an ideal target for this new technology for several reasons. First, IMRT offers the potential for improved tumor control through delivery of high doses to the target volume. Second, because of sharp dose gradients, IMRT results in the relative sparing of normal structures, such as the parotid glands, in the head and neck region. Third, organ motion is virtually absent in the head and neck region so, with proper immobilization, treatment can be accurately delivered. Although this is a relatively new technology, single-institution retrospective studies show better dosimetric profiles compared with conventional radiation techniques, as well as excellent clinical results. Salivary gland sparing using IMRT has also resulted in reduced incidence and severity of xerostomia, and this has been tested in a randomized trial against conventional radiotherapy for early-stage nasopharyngeal cancer. The results do confirm that IMRT does decrease xerostomia compared with conventional radiotherapy.