Radiation therapy (or radiotherapy) 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 and diagnosis). 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 and/or hormone therapy. The most common tumours treated with radiotherapy are breast cancer, prostate cancer, lung cancer, colorectal 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 success.
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 radioactive sources has the usual side effects associated with invasive proceedures.
Radiation Therapy can, to some extent, be regarded as a drug like any other. It is therefore useful to distinguish the total dose from the fractionation schedule. Radiation therapy is usually given daily, the dose depends primarily on tumor type, but many other factors such as whether radiation is given alone or with chemotherapy, before or after surgery, the success of surgery and its findings and many other reasons that are considered by the treating doctor (known as a radiation oncologist). The typical dose for a solid epithelial tumor may range from 50 to 70 Gray or more, while lymphomas (white cell) tumors might receive doses closer to 20 to 40 Gray given in daily doses (a daily dose is a fraction);In adults these are typically ~2 Gy (Gray (unit)) per fraction. These small frequent doses allow healthy cells time to grow back, repairing damage inflicted by the radiation. In short, total dose can be given in daily fractions using external beam radiation or the total dose can be given via other methods such as implants that deliver radiation continuously over a given timeframe. Depending on the implant type, it may be given as a fraction (e.g. High Dose Rate HDR) over minutes or hours or as another example permanent seeds may be implanted (such as in the prostate) which slowly deliver radiation until the seeds become inactive.
As mentioned above, the typical fractionation schedule is 2Gy/fraction, with 1 fraction/day for an adult patient. However, there are alternative fractionation schedules that have been tried. One of the best-known was the CHART (Continous Hyperfractionated Accelerated RadioTherapy) regime for lung cancer, which used 2 or 3 smaller fractions per day in the treatment of lung cancer. Although reasonably successful, this imposed huge strains on the departments delivering the service, as it required multiple treatments everyday, including weekends. In some paediatric cancers, fractionation schedules tend to give 1.5 - 1.7Gy/fraction. The reason for this is that fractionation effects the balance between acute and late toxicity, and the smaller the fraction, the smaller the late effects. Obviously late effects are of more concern in paediatric patients than adults.
How it works
Radiation therapy works by damaging the DNA of cells. The damage is caused by an electromagnetic, electron or proton beam ionizing the bases in the DNA breaking the DNA chain. Because cells have mechanisms for repairing DNA breakage, where the DNA is broken on both strands of the DNA are the most significant in modifying cell charactaristics. Because cancer cells generally are undifferentiated and stem cell-like, they reproduce more, and have an dimished ability to repair sublethal damage compared to most healthy differentiated cells. The DNA damage is inherited through cell division, accumulating damage to the cancer cells, causing them to die or reproduce more slowly. Proton radiotherapy works by sending protons with varying kinetic energy to precisely stop at the tumor. Being researched is antiproton radiotherapy which would require fewer treatments than proton radiotherapy.
Tumours don't repair the radiation damage as well as nonmalignant tissue.
Most cells, however, die only during a specific phase of cellular reproduction, which has many curious implications:
Three main divisions of radiotherapy are external beam radiotherapy (XBRT) 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 and 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).