Overview of image-guided radiation therapy

Radiotherapy has evolved through a series of revolutions in the last few decades and it is now possible to produce highly conformal dose distribution by using techniques such as IMRT, SRS/ SRT. High dose conformity demands better target localization accuracy. But, the target changes its position in intra as well as in inter-fractional time scale and posing difficulty in achieving accurate patient positioning. Radiotherapy has been an image-guided intervention since its inception. Imaging has a major role to play at each step i.e. diagnosis, staging, simulation of beam portals, treatment planning, beam portal verification and follow-up of the patient. Although imaging is an integral part in delivering radiation effectively, in current literature the term IGRT or IGIMRT is employed to refers to new emerging radiation planning, patient setup, and delivery procedures that integrate cutting-edge image-based tumor definition methods, patient positioning devices, and/or radiation delivery guiding tools