abstract: Image guided radiation therapy (IGRT) for the treatment of cancer has become a reality with the availability of imaging capabilities in the radiation treatment room with the patient in the actual treatment position, where volume images can be acquired on a daily basis. These images can potentially guide radiation therapy in the following two aspects. Firstly, the direct reference of the images obtained with the patient in the treatment position to the treatment machine coordinates can substantially reduce the geometric uncertainty of internal structures. With the additional real time tracking and adjustment capabilities, more precise radiation will then be delivered with high dose to target volume while sparing nearby critical structures with the latest delivery technology in radiation therapy: intensity modulated radiation therapy (IMRT). Secondly, with the images available on a more frequent basis, analysis will yield tumor response during radiation treatments in the early stages that will allow adjustment of treatment techniques (fraction size, radiation modality, radiation treatment plan modification, etc.). In order to achieve wide-spread use of these latest image and delivery technologies to their fullest capabilities, sufficiently powerful and efficient strategies and software tools have to be available. Among the needed, for accurate and efficient adjustments, tools that allow registration of internal structures between image sets are mandatory. Since internal structures are expected to deform, registration technology that incorporates deformation has to be employed. To evaluate tumor size variation during radiation therapy treatment courses, one needs efficient and accurate tools that define structures withwithout human intervention. Other general essential tools are image manipulation capabilities that include proper image filtering for maximum information rendering. If radiation therapy treatment plan modification is deemed necessary, tools have to be included for the ability to create radiation treatment plans with full dosimetric calculation capability using the online acquired geometry. In this talk, I will describe the adaptive radiotherapy process, some of the software tools implemented and the ones that are still needed.