During external beam radiation therapy, a beam (or multiple beams) of radiation is directed through the skin to the cancer and the immediate surrounding area to destroy the tumor and any nearby cancer cells. To minimize side effects, the treatments are typically given five days a week, Monday through Friday, for a number of weeks. This allows enough radiation to get into your body to kill the cancer while giving healthy cells time to recover.
The radiation beam is usually generated by a machine called a linear accelerator, or linac. The linear accelerator is able to produce high-energy X-rays or electrons for the treatment of your cancer. Using treatment planning computers and software, your treatment team controls the size and shape of the beam, as well as how it is directed at your body, to effectively treat your tumor while sparing the surrounding normal tissue. There are several special types of external beam radiation therapy used for specific types of cancer.
Tumors are not all the same; they come in different shapes and sizes. Also, every patient’s body is unique. Three-dimensional conformal radiation therapy, or 3-D CRT, uses computers and special imaging techniques such as CT, MR or PET scans to show the size, shape and location of the tumor as well as surrounding organs. Your radiation oncologist can then precisely tailor the radiation beams to the size and shape of your tumor with special shielding. Because the radiation beams are carefully targeted, nearby normal tissue receives less radiation and is able to heal better.
Intensity modulated radiation therapy, or IMRT, is a specialized form of 3-D CRT that allows radiation to be specifically shaped to cover the tumor and spare more normal tissue. With IMRT, the radiation beam can be broken up into many “beamlets,” and the intensity of each beamlet can be adjusted individually. Using IMRT, it may be possible to further limit the amount of radiation received by healthy tissue near the tumor. In some situations, this may also safely allow a higher dose of radiation to be delivered to the tumor.
Radiation oncologists use image guided radiation therapy, or IGRT, to more accurately deliver radiation to the cancer. IGRT involves conformal radiation treatment guided by imaging, such as CT, ultrasound or X-rays, taken in the treatment room just before the patient is given the radiation treatment on a daily basis. Because tumors can move between treatments, due to differences in organ filling or movements while breathing, IGRT allows for better targeting of cancer cells. You will first undergo a CT scan as part of the planning process. The information from the CT scan is then transmitted to a computer in the treatment room to allow the team to compare the earlier image with the images taken just before treatment. During IGRT, the team compares these images to see if the treatment needs to be adjusted. In some cases, doctors will implant a tiny marker in or near the tumor to help localize the treatment area. IGRT allows the team to better target the cancer while avoiding nearby healthy tissue.
Stereotactic radiotherapy is a specialized technique that allows your radiation oncologist to use extremely focused beams of radiation to destroy certain types of tumors using higher doses than with daily radiation treatments. Since the beam is so precise, your radiation oncologist may be able to spare more healthy tissue. In selected cases, stereotactic treatments can be used to retreat tumors that have received radiation before.
Stereotactic radiotherapy was first developed to treat brain tumors in a single dose, sometimes called stereotactic radiosurgery or SRS. In addition to treating cancers, radiosurgery can also be used to treat benign tumors and certain noncancerous neurologic conditions. In some cases, using more than a single dose may help decrease the risk of side effects with stereotactic radiation therapy.
Treatment outside the brain is called stereotactic body radiation therapy (SBRT). It is typically given in a few treatments. Often used for the lung, spine or liver, SBRT may allow radiation to be given in a way that is safer and more effective than other radiation techniques.
Because specialized treatments with stereotactic radiation are often much higher doses than daily radiation treatment, additional precision and quality assurance is necessary. This involves using very secure immobilization of the head or body as well as using techniques that allow the radiation beam to account for organ motion during treatment. Stereotactic radiation offers new ways for your doctor to treat cancer. In many clinics, these technologies are called by the name of the vendor that makes it or the product name.
Radiation therapy given during surgery is called intraoperative radiation therapy, which can be helpful when vital normal organs are very close to the tumor. During an operation, a surgeon temporarily moves the normal organs out of the way so radiation can be applied directly to the tumor. This allows your radiation oncologist to avoid exposing those organs to radiation.
Proton beam therapy is a form of external beam radiation treatment that uses protons rather than electrons or X-rays to treat certain types of cancer and other diseases. The physical properties of the proton therapy beam allow the radiation oncologist to more effectively reduce the radiation dose to nearby healthy tissue.
Like proton therapy, neutron beam therapy is a specialized form of external beam radiation therapy. It involves using neutrons rather than electrons or X-rays to treat certain types of cancer. It is often used to treat certain tumors that are radioresistant, meaning they are very difficult to kill using conventional X-ray radiation therapy. Neutrons have a greater biologic impact on cells than other types of radiation. Used carefully, this added impact can be an advantage in certain situations. Neutron therapy is available at only a few centers in the country.