Radiation therapy has the capability to conform radiation fields delivered to tumours much more accurately because of developments in therapy equipment in recent decades. This can help to reduce doses to normal tissues considerably. Successful delivery requires the patient to be in the same position on the couch as in the treatment plan. Therefore, images are taken at regular intervals, frequently at every treatment fraction and compared with images used for planning, and this is referred to as image guided radiation therapy (IGRT). If more imaging with x rays is carried out, this exposes patients to additional doses to tissues surrounding the tumour that carry a risk of inducing secondary cancers. The reductions in high dose treatment margins that can be achieved with IGRT need to be balanced against risks from greater imaging doses. ICRP Task Group 116 is preparing guidance on IGRT, and has used the ICRP mentorship programme to undertake surveys of imaging practices and to trial ways for measuring cone beam computed tomography (CBCT) doses that could be widely applied. Results from the projects are feeding into development of the report with recommendations to facilitate improvements in the application and optimisation of radiological protection in the use of imaging in radiotherapy.