**6. Adaptive radiotherapy**

Adaptive radiotherapy is a technique in which any volumetric or spatial variations in tumor volume or OARs, the morphological changes are taken into account through re-planning of patients at certain defined intervals during the course of treatment. The re-planning helps in adapting to the anatomical changes in tumor and OARs such as parotids and optimizing the plan to provide adequate tumor coverage and minimize the dose to OARs [28]. These variations are corrected on a daily basis through modifications in the treatment plan with the help of image guidance. Routine in-room volumetric images are acquired and sent to the treatment planning system for re-planning. The contours of the daily in-room CT are superimposed with the reference planning CT to account for any variation in the anatomy or set up, through deformable image registration software. A new treatment plan conforming to the current changes in anatomy, if any, is generated through automated deformable registration software and the adapted plan is transferred to the machine for treatment. The new plan is implemented either in online mode after online correction or in offline mode, where the corrections are implemented after some time [29]. Adaptive radiotherapy has offered dosimetric benefits in HNC and its clinical benefits have also been proven by a few studies [30].

Therefore medical fraternity now has a better understanding of radiation related toxicities in head and neck cancers, so it is truly gratifying to deliver radiotherapy by such innovative techniques where it really matters.

*Volumetric and Dosimetric Inconstancy of Parotid Glands and Tumor in Head and Neck Cancer… DOI: http://dx.doi.org/10.5772/intechopen.104745*
