Radiation Therapy

Radiation therapy (also called radiotherapy) is a cancer treatment that uses high doses of radiation to kill cancer cells and shrink tumors.

At high doses, radiation therapy kills cancer cells or slows their growth by damaging their DNA. Cancer cells whose DNA is damaged beyond repair stop dividing or die. When the damaged cells die, they are broken down and removed by the body.

Radiation therapy does not kill cancer cells right away. It takes days or weeks of treatment before DNA is damaged enough for cancer cells to die. Cancer cells continue to die for weeks or months after radiation therapy ends.

Many of the types of radiation therapy will require a short planning session in the equipment to verify the radiation plan.

Types of Radiation Therapy

There are two main types of radiation therapy – external beam and internal.

The type of radiation therapy that you may have depends on many factors, including:


External Beam Radiation Therapy (EBRT)

EBRT comes from a linear accelerator that aims radiation at your cancer. The machine is large but can move around you, sending radiation to a part of your body from many directions.

EBRT is a local treatment which means it treats a specific part of your body. For example, if you have cancer in your lung, you will have radiation only to your chest, not to your whole body.

There are many types of ERBT, all of which share the goal of delivering the optimal 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.

3-D Conformal Radiation Therapy (3D-CRT)

3-D CRT is a common type of EBRT. It uses images from CT and optionally MRI or PET scans to precisely plan the treatment area. The process is called simulation. A computer program is used to analyze the images and to design radiation beams that conform to the shape of the tumor.

3-D CRT 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.

Intensity Modulated Radiation Therapy (IMRT)

IMRT is a type of 3-D CRT. Like 3-D CRT, radiation beams are aimed at the tumor from several directions, either as a static delivery or rotational where the beam is constantly moving around the patient

IMRT uses many smaller beams than 3-D CRT and the strength of the beams in some areas can be changed to give higher doses to certain parts of the tumor.

Image Guided Radiation Therapy (IGRT)

IGRT is a type of EMRT. It uses imaging before, during and after treatment to accurately position the patient and the tumor volume(s) to the treatment planning image.

During treatment, you will have repeated scans, such as CT and optionally 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.


Tomotherapy® is a type of treatment machinery that delivers an EBRT in a helical fashion.

Tomotherapy® machines take images of the tumor right before the treatment session to allow for very precise tumor targeting and sparing of normal tissues. Tomotherapy® treatment machinery rotates around you during treatment, delivering radiation in a spiral pattern, slice by slice.

Stereotactic Radiosurgery (SRS)

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, you have other health concerns or if the tumor cannot safely be reached with surgery. Cyber Knife and Gamma Knife is a type of stereotactic radiosurgery treatment machine but SRS can be delivered by other machines including a linear accelerator.

Stereotactic Body Radiation Therapy (SBRT)

SBRT 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.

Proton Beam

Proton therapy is an advanced form of radiation treatment that uses protons instead of X-rays.

In regular radiation therapy, the beam of energy goes into the body, through the tumor, and out the other side. This “exit dose” of radiation might affect healthy tissue beyond the tumor. Protons, in contrast, are larger particles than those used in regular radiation. They release more of their energy within the tumor itself.

After delivering the energy to the tumor, the protons stop: They do not exit the tumor or go into healthy tissue on the other side.

In this way, proton therapy reduces radiation exposure and potential damage to healthy tissue, especially in sensitive areas such as the brain, eyes, spinal cord, heart, major blood vessels and nerves.

Internal Radiation Therapy

Internal radiation therapy, also known as Brachytherapy, is a treatment in which a source of radiation is put inside your body. The radiation source can be solid or liquid. In this type of treatment, seeds, ribbons, or capsules that contain a radiation source are placed in your body, in or near the tumor. Like EBRT, brachytherapy is a local treatment and treats only a specific part of your body. With brachytherapy, the radiation source in your body will give off radiation for a limited period of time.

The major advantage of Brachytherapy is that very high doses of radiation can be delivered locally to the tumor in a relatively short period of time, while low doses are delivered to the surrounding tissue.