There are many types of external beam radiation therapy, all of which share the goal of delivering the highest prescribed dose of radiation to the tumor while sparing the normal tissue around it. Each type relies on a computer to analyze images of the tumor in order to calculate the most precise dose and treatment path possible.
Types of external beam radiation therapy include:
3-D conformal radiation therapy
What It Is
3-D conformal radiation therapy is a common type of external beam radiation therapy. It uses images from CT, MRI, and PET scans to precisely plan the treatment area, a process called simulation. A computer program is used to analyze the images and to design radiation beams that conform to the shape of the tumor.
How It Works
3-D conformal radiation conforms to the shape of the tumor by delivering beams from many directions. The precise shaping makes it possible to use higher doses of radiation to the tumor while sparing normal tissue.
Treatment Schedule
Most people have treatment once a day, Monday through Friday. The number of treatments vary from person to person based on details about your cancer, such as the type and stage of the cancer and the size and location of the tumor.
Intensity-modulated radiation therapy (IMRT)
What It Is
IMRT is a type of 3-D conformal radiation therapy.
How It Works
Like 3-D conformal radiation, radiation beams are aimed at the tumor from several directions.
IMRT uses many more smaller beams than 3-D conformal and the strength of the beams in some areas can be changed to give higher doses to certain parts of the tumor.
Treatment Schedule
Most people have treatment once a day, Monday through Friday. The number of treatments vary from person to person based on details about your cancer, such as the type and stage of the cancer and the size and location of the tumor.
Image-guided radiation therapy (IGRT)
What It Is
IGRT is a type of IMRT. However, it uses imaging scans not only for treatment planning before radiation therapy sessions, but also during radiation therapy sessions.
How It Works
During treatment, you will have repeated scans, such as CT, MRI, or PET scans. These scans are processed by computers to detect changes in the tumor’s size and location. The repeated imaging allows for your position or the radiation dose to be adjusted during treatment, if needed. These adjustments can improve the accuracy of treatment and help spare normal tissue.
Treatment Schedule
Most people have treatment once a day, Monday through Friday. The number of treatments vary from person to person based on details about your cancer, such as the type and stage of the cancer and the size and location of the tumor.
Tomotherapy®
What It Is
Tomotherapy® is a type of IMRT that uses a machine that is a combination of a CT scanner and an external-beam radiation machine.
How It Works
Tomotherapy® machines take images of the tumor right before treatment sessions to allow for very precise tumor targeting and sparing of normal tissues. It rotates around you during treatment, delivering radiation in a spiral pattern, slice by slice. Tomotherapy® might be better at sparing normal tissue than 3-D conformal radiation therapy, but it has not been tested in clinical trials to be sure.
Treatment Schedule
Most people have treatment once a day, Monday through Friday. The number of treatments vary from person to person based on details about your cancer, such as the type and stage of the cancer and the size and location of the tumor.
Stereotactic radiosurgery
What It Is
Stereotactic radiosurgery is the use of focused, high-energy beams to treat small tumors with well-defined edges in the brain and central nervous system. It may be an option if surgery is too risky due to your age or other health problems or if the tumor cannot safely be reached with surgery. GammaKnife is a type of stereotactic radiosurgery.
How It Works
You will be placed in a head frame or some other device to make sure you do not move during treatment. In stereotactic radiosurgery, many small beams of radiation are aimed at the tumor from different directions. Each beam has very little effect on the tissue it passes through, but a precisely targeted dose of radiation is delivered to the site where all the beams come together.
Treatment Schedule
Treatment schedules can vary, but treatment is usually given in one dose. In some cases, you may receive up to five doses, given once per day.
Stereotactic body radiation therapy
What It Is
Stereotactic body radiation therapy is similar to stereotactic radiosurgery, but it is used for small, isolated tumors outside the brain and spinal cord, often in the liver or lung. It may be an option when you cannot have surgery due to age, health problems, or the location of the tumor.
How It Works
As in stereotactic radiosurgery, stereotactic body radiation therapy uses special equipment to hold you still during treatment. It delivers a highly precise beam to a limited area.
Treatment Schedule
Tumors outside of the brain are more likely to move with the normal motion of the body, such as with breathing or digesting. Therefore, the radiation beams cannot be targeted as precisely as they are in stereotactic radiosurgery. For this reason, stereotactic body radiation is usually given in more than one dose. You may have up to five doses, given once per day.