Radiation Therapy: Which type is right for me?
There are two main types of radiation therapy. External radiation therapy is when a beam of radiation is directed into the body. It may also be called x-ray therapy, 3D conformal radiation, intensity-modulated radiation therapy (IMRT), cobalt, photon, or proton therapy. Internal radiation therapy is when a radioactive source is placed inside the body, in or near the tumor. This is called brachytherapy or implant therapy.
External radiation therapy is named after the type of radiation particles that are used to give the treatment:
Photon, electron, and proton therapy all damage cancer cells. Each type does have certain advantages and disadvantages. Your treatment team will work together to pick the best type of radiation therapy for your type of cancer.
Photon and electron radiation are found in most radiation centers and are the most used. Protons are at only some cancer centers, with new proton therapy centers being built and others in the planning stage.
Photon beams are the same type of beam used in x-ray machines, like those used to take chest x-rays. However, in radiation therapy, much higher energy photon beams are used. Photons can be used in many different types of radiation therapy.
Two-Dimensional Photon Therapy ("Conventional" Radiation Therapy)
When 2D, or conventional radiation therapy is used, x-ray films are used to guide and position the radiation beams. A machine called a “fluoroscopic simulator” is often used to plan the radiation treatments. The bones seen on the x-rays are used as landmarks to find where the tumor is and where to position the radiation beams to treat the tumor.
Planning does not take a long time and patients can often start treatment within a week. It is often used for urgent treatments.
3D Conformal Radiation Therapy
Many hospitals now have the ability to use a CT scanner (Cat Scan) to plan radiation treatments. This is called 3D conformal radiotherapy. CT-guided therapy allows the tumor and normal organs to be looked at in three dimensions instead of using the "flat" image of an x-ray (in “conventional” radiation therapy).
Intensity Modulated Radiation Therapy (IMRT)
IMRT is another way to deliver photons but it spares more healthy tissue. Treatment planning for IMRT also begins with a simulation. Like 3D conformal therapy, the tumor and normal organs are outlined on the CT in 3D. Multiple beams are positioned around the person to deliver the radiation. However, in IMRT, these beams are divided into a grid-like pattern, separating the one big beam into many smaller "beamlets." These beamlets help to protect the healthy tissues.
Stereotactic Radiation Therapy (SRT)
SRT uses many different angles to focus the radiation at one small area and to deliver a high dose of radiation. The tissues around it receive a much lower dose, lowering the risk of side effects. There are two types of stereotactic radiation therapy: Stereotactic radiosurgery (SRS) and Stereotactic body radiation therapy (SBRT).
Brachytherapy is the use of a radioactive source, often one that releases photons. The source is put into the tumor (interstitial brachytherapy) or placed near the cancer, often in a body cavity (intracavity brachytherapy). Since brachytherapy is placed in, or very close to the tumor, the amount of normal tissue affected by the radiation is less. The dose of radiation released from the source is very high but much less in the nearby tissues.
Brachytherapy can only be used in cancers where a radioactive source can be placed safely and treat the tumor.
Orthovoltage was often used before linear accelerators became available for the treatment of many different tumors. Orthovoltage radiation uses lower energy photons to treat tumors that are found on or very close to the skin. The lower energy of orthovoltage beams doesn’t work well for deep tumors. Orthovoltage units are not used as much since these tumors can now be treated with electrons.
Electrons release their energy close to the skin's surface and are often used to treat superficial tumors (tumors close to the surface of the skin), such as skin cancers, keloids, and some lymph nodes. The radiation does not go much past the skin to deeper normal tissues. This treatment often replaces orthovoltage because it can be combined in the same machine as a linear accelerator. Electron radiation can be used to treat the skin of the entire body or only certain spots.
Proton therapy is a type of radiation that uses a particle, the proton, to deliver radiation while keeping the dose low to nearby healthy tissue. A large space used to be needed to house a proton machine. Smaller machines are being made making it easier to find clinics that offer proton therapy.
The advantage of protons is that they enter the body, release small amounts of radiation to the healthy tissues, deliver large amounts of radiation to the tumor, and very little radiation is released past that point.
There are many types of radiation therapy. Your radiation care team will consider your treatment goals, type of tumor, and where your tumor is when deciding which type of radiation is best for you. Talk with your radiation care team about any questions or concerns you might have.