There are three main types of radiation therapy: external beam radiation, internal radiation and radiopharmaceuticals. Each of these types will be considered in more detail below.
External Beam Radiation Therapy
This is the most common type of radiation used in the treatment of cancer and uses an external machine away from the body to direct radiation towards the area of the body affected by cancer. It is ideal for treating large areas or targeting different parts of the body simultaneously. Although it is aimed at the cancerous tissue, usually it also affects the surrounding normal tissue.
Three-dimensional conformal radiation therapy (3D-CRT) is a specialized technique that uses a realistic visualization of the tumor. It involves radiation targeted precisely to the tumor to minimize exposure of normal tissues to the radiation. It is essential that the imaging is accurate, as any part of the tumor that is unmapped will not be treated effectively.
Intensity modulated radiation therapy (IMRT) also uses a 3-dimensional map of the tumor, but aims photons towards the tumor from several directions with the ability to control the intensity of each beam. This allows greater dose control, with higher intensity to the tumor and less radiation to surrounding tissues. Similar to 3D-CRT, the patient is required to stay in the same position throughout treatment and unmapped areas of the tumor will not be targeted.
Image-guided radiation therapy (IGRT) allows oncologists to take images of the tumor immediately before therapy is administered and make adjustments to the therapy accordingly.
Intensity modulated proton therapy (IMPT) uses protons rather than photons to target the tumor. To date, it is unclear if protons or photons are more effective in radiation therapy.
Stereotactic radiotherapy uses a machine to focus hundreds of different narrow radiation beams at the tumor from different directions. This also involves accurate imaging to determine when the beams should be directed to effectively target the tumor and minimize exposure of other tissues.
Internal Radiation Therapy
Also known as brachytherapy, this type involves a source of radiation placed near the area to be treated with radiation, to minimize travel time of the beam and risk of damage to other tissues.
Interstitial radiation refers to when the radiation source is put in a position inside or right next to the tumor, using forms of seeds or tubes. Intracavitary radiation involves the placement of radioactive material inside a body cavity like the chest, rectum, uterus or vagina.
Permanent brachytherapy uses small pellets or seeds that are placed inside the tumor. These gradually emit radiation over a period of weeks or months and are conveniently small in size and cause minimal discomfort, so can be left in place on a permanent basis. Temporary brachytherapy involves the placement of slightly larger cylinders inside or near the tumor, which need to be removed after treatment due to their larger size that may cause discomfort.
Radiopharmaceuticals are types of drugs that contain radioisotopes, which can be administered to the body via an infection, an oral pill or placement inside a cavity, such as the rectum or vagina. These pharmaceuticals emit radiation, usually alpha and gamma particles that are designed to target the areas affected by tumor growth.
In most cases, this type of radiation is used to deliver radiation needed for imaging, but it can also be used in the treatment of specific tumors.