New ways to deliver radiation to tumors are making radiation therapy safer and more effective. Some of these methods are already in use, while others are undergoing further study before they can be approved for widespread use. And scientists around the world continue to look for better and different ways to use radiation to treat cancer.

Three-dimensional conformal radiation therapy (3D-CRT) uses MRI, CT, or PET scan pictures and special computers to very precisely map the location of a cancer in 3 dimensions. The patient is fitted with a plastic mold or cast to keep the body part still during treatment. The radiation beams are matched to the shape of the tumor and delivered to the tumor from several directions. This spreads out the entry and exit routes of the radiation to reduce the amount of radiation that goes though any one area of normal tissue. By aiming the radiation more precisely, it may be possible to reduce radiation damage to normal tissues and better fight the cancer by increasing the radiation dose to the cancer. Many medical centers now use 3D-CRT to treat different kinds of cancer.

Intensity modulated radiation therapy (IMRT) is an advanced form of external radiation therapy that uses photon beams. As with 3D-CRT, computer programs are used to precisely map out the tumor in 3 dimensions. But along with aiming photon beams from several directions, the intensity (strength) of the beams can be adjusted. This gives even more control over decreasing the radiation reaching sensitive normal tissues while delivering a higher dose to the cancer. Because of its precision, it is even more important that a person remain in the right place and be perfectly still during treatment. This usually requires that a special cast or mold be made to keep the body in place during treatment. IMRT is available mainly in major cancer centers. Because IMRT uses a higher total dose of radiation, it may slightly increase the risk of second cancers later on. This is something researchers are looking into.

A related technique, conformal proton beam radiation therapy, uses proton beams instead of x-rays. Protons are parts of atoms that cause little damage to tissues they pass through but are very good at killing cells at the end of their path. This means that proton beam radiation may be able to deliver more radiation to the cancer while reducing side effects on nearby normal tissues. Protons can only be put out by a special machine called a cyclotron or synchrotron. Installing this machine costs millions of dollars and requires expert staff. Because of this, proton beam therapy can be expensive, and very few treatment centers in the United States offer it. More studies are needed to compare outcomes between proton and photon treatment so that each is used for the cancer type for which it works best.

Stereotactic radiosurgery or stereotactic radiation therapy delivers a large, precise dose of radiation to a small tumor area. The term "surgery" may be confusing because no cutting is involved. Some tumors that started from or spread to the brain are treated with this technique.

A box-shaped head frame is attached to the skull to hold it still and allow for precise aiming of radiation beams. Once the exact location of the tumor is mapped (using CT or MRI scans), radiation beams from a machine called a Gamma Knife^® are focused at the tumor from hundreds of different angles for a short time. The process may be repeated if needed. Another approach that is much like this uses a movable linear accelerator that is controlled by a computer. Instead of delivering many beams at once, the linear accelerator moves around to deliver radiation to the tumor from different angles. Several machines work in this way, with names such as X-Knife^®, CyberKnife^®, and Clinac^®.

While these techniques are most commonly used for brain and spinal cord tumors, researchers are looking for ways to use them with other types of cancer too.

Intraoperative radiation therapy (IORT) is the delivery of radiation to the cancer during surgery. The radiation may be given externally or internally, and it is often used along with a course of external radiation given before or after the operation.

IORT is useful for abdominal (belly area) or pelvic cancers that cannot be completely removed (such as those that have grown close to vital body parts) and in cancers that tend to grow back after treatment. As much tumor is removed as possible and one large dose of radiation is directed right at the tumor site. Normal tissues can be moved out of the way and protected, so IORT reduces the amount of tissue that is exposed to radiation. This allows a higher dose of radiation to reach the cancer. IORT is delivered in a special operating room lined with radiation-shielding walls.

Hyperthermia refers to the use of heat to treat cancer. Heat has been found to kill cancer cells, but when used alone it does not destroy enough cells to cure the cancer. Heat created by microwaves and ultrasound is being studied in combination with radiation and appears to improve the effect of the radiation. For more information, see our document, Hyperthermia.

Radiosensitizers are drugs that make cancer cells more sensitive to radiation. Some chemotherapy drugs already in use (such as 5-fluorouracil or 5-FU) are known to be radiosensitizers. Researchers are trying to find new substances that will make tumors more sensitive to radiation without affecting normal tissues.

Radioprotectors are substances that protect normal cells from radiation. These types of drugs are useful in areas where it is hard not to expose vital normal tissues to radiation when treating a tumor, such as the head and neck area. Some radioprotectors, such as amifostine (Ethyol^®), are already in use, while others are being studied in clinical trials.

Go back to Radiation Principles.

Last Medical Review: 07/17/2009
Last Revised: 07/17/2009