The treatment of disease (mainly CANCER) with penetrating RADIATION using X-rays, beta rays or gamma rays, either produced by linear accelerator machines or given off by radioactive isotopes (see ISOTOPE), although the latter is rarely used now.

Beams of radiation may be directed at the tumour from a distance, or radioactive material – in the form of needles, wires or pellets – may be implanted in the body. Some germ-cell tumours (see SEMINOMA; TERATOMA) and lymphomas (see LYMPHOMA) are particularly sensitive to irradiation which therefore forms a major part of management, particularly for localised disease. Many head and neck tumours, gynaecological cancers, and localised prostate and bladder cancers are curable with radiotherapy. Radiotherapy is also valuable in PALLIATIVE CARE, chiefly the reduction of pain from bone metastases (see METASTASIS). Side-effects are potentially hazardous and these have to be balanced against the substantial potential benefits. Depending upon the type of therapy and doses used, generalised effects include lethargy and loss of appetite, while localised effects – depending on the area treated – include dry, itchy skin; oral infection (e.g. thrush – see CANDIDA); bowel problems; and DYSURIA.