Radiotherapy: technical aspects

Radiotherapy is involved in the treatment of at least 40% of cancer patients. Whereas palliative radiotherapy is typically given over 1–10 treatments, radical treatments can extend over 4–8 weeks. Radiation is delivered using external beam machines or by inserting radioactive isotopes. Localization of tumours has been transformed with spiral computed tomography, magnetic resonance imaging and positron emission tomography scanning. Modern imaging, computing and delivery systems have led to dramatic improvements in external-beam radiotherapy such as intensity-modulated radiotherapy (IMRT). Image-guided radiotherapy (IGRT) increases accuracy by imaging moving targets during treatment. Stereotactic radiotherapy allows very high doses to be delivered very precisely in a small number of treatments and is used for both intra- and extra-cranial lesions.