Image guidance in radiotherapy

Imaging has been integral to radiotherapy for decades. However, it has been within the last 20 years that phrases such as ‘image guidance’ have become part of mainstream radiotherapy vocabulary, and the use of all available imaging modalities within radiotherapy more common. So what is meant by ‘image guidance in radiotherapy’? This was one of the questions that the National Radiotherapy Implementation Group considered as part of its 2012 report. The resulting definition reflected how imaging is crucial within the whole of the radiotherapy process: ‘Image guided radiotherapy (IGRT) is any imaging at pretreatment and delivery, the result of which is acted upon, that improves or verifies the accuracy of radiotherapy.’ Figure 1 demonstrates how imaging is embedded in the radiotherapy process. At the policy level, the Department of Health Cancer Policy Team in the report Radiotherapy Services in England 2012 states unequivocally: “All patients should have a form of image guidance as part of their radiotherapy treatment episode,” (there are similar policies for the devolved nations). This article discusses IGRT in the context of its being integral to high quality radiotherapy.