This chapter discusses clinical applications of imaging equipment with relation to imaging science aspects. It describes factors influencing choices in equipment in relation to different treatment techniques and anatomical sites. Radioisotope imaging generally provides a two-dimensional image. As radiotherapy plans generally require volumetric images with a high spatial resolution, radioisotope imaging is more commonly used at diagnosis stage and to determine the staging of the disease, rather than defining an exact target volume for radiotherapy treatment. In a similar way to radioisotope imaging, positron emission tomography images provide functional information. The majority of radiotherapy departments will have one or a number of dedicated radiotherapy planning computed tomography (CT) scanners within the department used solely for the planning of radiotherapy treatments. A limitation of CT imaging can be artefacts produced due to a patient's normal breathing motion. Radiation fields used to treat whole breast or bone metastases target volumes are often quite large in modern radiotherapy terms.