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What are the different types of radiation therapy?
Radiation therapy is given through different methods, depending on the type of disease, its location, and your general health. Often, radiation therapy is used in combination with other treatments. The following are some of the different types of radiation therapy with brief explanations of their goals:
- External Radiation (External Beam Therapy)
With external radiation (external beam therapy), radiation is administered by a medical linear accelerator (invented at Stanford) that points the radiation directly at the tumor. You will lie on an x-ray table with the same immobilization devices in place that were used in the simulation process. A specially-trained radiation therapist controls the machine. Special shields may be made to protect the tissue surrounding the treatment area, or sometimes protective devices are incorporated into the “head” of the treatment machine.
External beam radiation therapy is delivered in multiple “fractions”. Usually, treatments are delivered on a daily basis, five days per week. The duration will depend on the type of cancer and its location. At the outset, confirmatory x-rays are taken in the treatment position to confirm that the treatments have been designed properly. These are then reviewed by the radiation oncologist. Subsequently, each daily treatment requires only several minutes and you will not likely be in the treatment room any longer than 15 minutes.
Radiation treatments are painless, you feel absolutely nothing during a treatment. Although you are alone in the treatment room while the machine is turned on, you will be monitored with audio and video by the radiation therapist.
The two major types of radiation beams are photons and electrons. Both are produced by the linear accelerator. In general, photons (x-rays) travel completely through a body or tissue. Electrons penetrate to only a defined depth. Photons or electrons are chosen depending upon the location of a tumor. They may be used, in combination.
- Three-Dimensional Conformal Radiation Therapy
The use of CT scanning in the treatment simulation process permits the development of a three-dimensional treatment plan that allows the design of a complex combination of radiation beams focusing on a cancer. This is particularly useful in treating cancers that are adjacent to vital structures or near organs that are sensitive to the effects of radiation.
Completion of a three-dimensional treatment plan requires CT scanning equipment, essential computer hardware and software, as well as skilled radiation oncologists and radiation dosimetrists.
- Intensity Modulated Radiotherapy (IMRT)
IMRT is one step further in the development of 3-D conformal radiation therapy. This is an advanced technique of dose calculation and treatment delivery that permits the advanced design of treatment fields to maximize the differential in dose delivered to tumors and normal tissues.
Many of the concepts of IMRT were developed at Stanford and Stanford has the longest experience in Northern California in using this technology. It is especially useful in the management of prostate and head and neck cancers.
- Stereotactic Radiation Therapy or Radiosurgery
Stereotactic radiation therapy or radiosurgery is a specialized form of external beam therapy. For this technique, multiple highly focused radiation beams are delivered from multiple directions with pinpoint accuracy.
This form of treatment is often used for tumors or other growths within the skull, including arterio-venous malformations and acoustic neuromas. It may also be used for cancer or non-cancerous growths along the spine or even in other parts of the body. Radiosurgery generally implies a single high dose or just a few high dose treatments. These treatments may be administered with a conventional medical linear accelerator or with a specially designed linear accelerator called the “CyberKnife."
- Internal Radiation (Brachytherapy, Implant Radiation)
With internal radiation (brachytherapy, implant radiation), a high dose of radiation is given inside the body as close to a cancer as possible. The radiation device may be implanted directly into a tumor or placed into a body cavity.
These techniques are commonly used for treatment of prostate or gynecological (cervix, uterus or vagina) cancers. Some internal radiation treatments stay in the body temporarily and may require brief hospitalization (low dose rate brachytherapy) or not (high dose rate brachytherapy); other internal treatments stay in the body permanently (such as prostate “seed” implants), although the radioactive seeds lose their radiation within a short period of time. In some cases, both internal and external radiation therapies are used.
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