Radiation therapyRadiation therapy
) is the medical
use of ionizing radiation
as part of cancer treatment
to control malignant cells
(not to be confused with radiology
, the use of radiation in medical imaging
). Although radiotherapy is often used as part of curative therapy, it is occasionally used as a palliative treatment
, where cure is not possible and the aim is for symptomatic relief. Other rare uses are to wipe out the immune system prior to transplant to reduce the incidence of tissue rejection, called TBI or Total Body Irradiation; to calm hyperactive muscles -- such as might cause twitchy eyes -- with mild superficial treatments; and to form scar tissue around a STENT to reinforce the vascular wall.
Radiotherapy is commonly used for the treatment of tumours. It may be used as the primary therapy. It is also common to combine radiotherapy with surgery and/or chemotherapy. The most common tumours treated with radiotherapy are breast cancer, prostate cancer, lung cancer, rectal cancer, head & neck cancers, gynaecological tumours, bladder cancer and lymphoma, although the cancer's stage (progress) and invasion into lymph nodes, as well as and other health and (unfortunately) monetary factors affect which treatment will have the greatest possibility of sucess.
Radiation therapy is commonly applied just to the localised area involved with the tumour. Often the radiation fields also include the draining lymph nodes. It is possible but uncommon to give radiotherapy to the whole body, or entire skin surface.
Although the actual treatment is painless, using external radiation (see below) to tackle tumours inevitably leads to side effects. The side effects can occur during treatment (acute side effects such as soreness and redness over the affected area; nausea and vomiting) or long after treatment has finished (late side effects reflecting permanent organ damage). Implanting radiactive sources has the usual side effects associated with invasive proceedures.
Radiation therapy is usually given daily for up to 35-38 fractions (a daily dose is a fraction). These small frequent doses allow healthy cells time to grow back, repairing damage inflicted by the radiation. Tumours don't repair the radiation damage as well as non-cancerous tissue. Most cells, however, die only during a specific phase of cellular reproduction, which has many curious implications:
- Some slowly growing tumours (for example, prostate) may be treated best by not treating them at all, since the patient will likely die from other causes, such as old age, before the cancer kills.
- It is thought that tumours which outgrow their blood supply, causing a low-oxygen state known as hypoxia, reproduce less frequently and are therefore more resistant to the effects of radiation.
- Some brain tumours do not die at extremely high doses. It is an open subject as to to the mechanism by which they survive, but perhaps they do not reproduce in the usual way.
Three main divisions of radiotherapy are external beam radiotherapy
or teletherapy, brachytherapy
or sealed source radiotherapy
and unsealed source radiotherapy
. The differences relate to the position of the radiation source; external is outside the body, while sealed & unsealed source radiotherapy has radioactive material delivered internally. Brachytherapy sealed sources are usually extracted later, while unsealed sources are injected into the body.
Roughly half of the 2500 worldwide radiotherapy clinics are in the US (as of 2001).
See also: Cancer
-- Surgical Oncology -- Gene Therapy -- Cancer Vaccine