From IMRT to IGRT: frontierland or neverland?

The recent enthusiasm for real-time image guidance in radiotherapy (IGRT) is in part due to the commercial availability of advanced on-line imaging technologies. Perhaps more important than its potential to improve conventional radiotherapy, IGRT may lead to a paradigm shift in facilitating hypo-fractionated or single-dose treatment. However, there are uncertainty regarding features and approaches of competing IGRT systems and as to whether a sub-set of the features of an ideal IGRT system would suffice for specific disease sites and clinical applications. Clinical studies are necessary for the quantification of benefit needed for evidence-based medicine.