Radiotherapy: technical aspects

Radiotherapy is an important cancer treatment: in patients who are cured of cancer, radiotherapy contributes to cure in around 40% of cases. Radiotherapy also has an important role in improving symptoms in individuals with incurable cancer. Whereas palliative radiotherapy is typically given over 1–10 treatments, radical treatments can extend over 4–8 weeks. Radiation is often delivered externally by machines called linear accelerators. It can also be delivered using brachytherapy, where radioactive implants are placed in or close to a tumour, or systemic isotopes, which are swallowed or injected and then locate and destroy cancer cells. Modern imaging, computing and delivery systems have led to dramatic improvements in external-beam radiotherapy. Treatment aims to accurately and precisely deliver high radiation doses to tumour tissue and minimize doses received by surrounding normal tissues. Image-guided radiotherapy increases accuracy by evaluating tumour motion and position during treatment. Stereotactic radiotherapy delivers very high radiation doses very accurately in a small number of treatments and can be used for intra- and extracranial lesions. New developments, including magnetic resonance imaging-based treatment systems and adaptive planning, aim to further improve treatment accuracy and precision, with the ultimate aim of increasing cure and reducing toxicity.