Defining the radiation target on a daily basis

The delineation of the target volume for irradiation is a critical step in the radiotherapy process. Delivery of radiotherapy occurs over a fractionated course of many treatments. Variations in the position of the target volume may occur on a daily basis during treatment and so the procedure for defining the target volume on a single initial 'snapshot' computed tomography scan has been re-evaluated. Newer technologies of image-guided radiotherapy allow the development of on-line daily definition of the target volume prior to radiotherapy delivery.