Adaptive Image-Guided Radiotherapy for Head and Neck Cancer

Abstract

The natural goal for improvements in radiotherapy is to enhance locoregional control and reduce side effects. In recent years the technical developments in methods for tumor delineation and treatment delivery have improved both tumor coverage and healthy tissue sparing. Especially high precision conformal radiotherapy techniques such as intensity-modulated radiotherapy (IMRT) and stereotactic radiotherapy have enabled dose escalation to the target with decreased volume of healthy tissue irradiated to a high dose level. However, the consequence of the increasingly conformal dose distributions is enhanced sensitivity to changes in the patient from planning to treatment and during the course of fractionated radiotherapy. Setup errors and anatomical changes may cause deviations between planned and delivered dose distribution, which can lead to underdosage of tumor volume and/or overdosage of normal tissue if not properly corrected for. Most setup errors can be avoided by conventional measures such as rigid patient immobilization, and MV port fi lm, while the internal soft tissue deformations occurring because of weight loss, tissue shrinkage, breathing motion, or deformation of tumor/normal tissues require more sophisticated imaging and adaptive strategies. This may involve developing a new treatment plan on the basis of the new anatomic information. To this end, adaptive image-guided radiotherapy (IGRT) offers a possible solution and safety-net. The recent advances in treatment-room image-guidance technologies (as reviewed by Dawson and Jaffray (2007)) have facilitated convenient and frequent imaging of the patient anatomy throughout the treatment course, and thus form a basis for treatment plan adjustments to shape and position of target and organs at risk on a regular basis. The adaptive radiotherapy (ART) process in which the subsequent delivery can be modifi ed using a systematic feedback of the geometric and dosimet-ric information from previous fractions is still in an investigational phase of development for many tumor sites, including the head and neck region.