What is Radiation Therapy?
Posted 7/28/2010
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Radiation therapy often seems the most mysterious of cancer treatments. We understand how surgery works. We sort of understand how chemotherapy works and certainly see its impact. Hormonal theray, just those little pills, can also seem mild. but we have taken pills for lots of things, so it is familiar.
Lying down under this large machine, baring our bodies to it. and believing that strong treatment is delivered can be hard to appreciate. It is disconcerting that, after a lifetime of being told to avoid radiation exposure, we are choosing to take it daily. It is more disconcerting that, in spite of the reassurances about no scatter, all the techs leave the room and make sure the heavy door is closed before the machine is turned on.
This is an excellent explanation of ASCO's Cancer Net about radiation therapy.
Understanding Radiation Therapy
Last Updated: July 12, 2010
This is the first article in a three-part series, and it provides an overview of radiation therapy. Other articles in this series address what to expect when receiving radiation therapy and side effects of the treatment.
What is radiation?
Radiation is energy that travels through space in the form of subatomic particles or electromagnetic waves. The various types of radiation have different frequencies (speeds of repetition) at which they oscillate (swing back and forth in a steady rhythm). Radiation with a low frequency (and, thus, low energy) is described as non-ionizing and can come from sources such as AM/FM radios, televisions, microwave ovens, and heat lamps. Meanwhile, ionizing radiation—such as ultraviolet (UV) light from the sun and x-rays—oscillates at a high enough frequency to break chemical bonds in atoms. As a result, such high-energy x-rays or other particles can be used to kill cancer cells in a treatment called radiation therapy.
Radiation as therapy
A doctor called a radiation oncologist oversees radiation therapy, which usually consists of a specific number of treatments given over a specific time. The goal of this treatment is to kill cancer cells without harming the surrounding healthy tissue. It may be used as the main treatment or as an adjuvant therapy (treatment given after the main treatment to target any potential remaining cancer cells). Meanwhile, radiation therapy can also be used to shrink tumors and reduce pressure, pain, and other symptoms of cancer (called palliative radiation therapy) when it is not possible to completely eliminate the disease.
More than half of all people with cancer receive some type of radiation therapy. For some cancers, radiation therapy alone is an effective treatment, while other types of cancer respond best to combination treatment approaches that may include radiation plus surgery, chemotherapy, or immunotherapy.
Types of radiation therapy
External-beam radiation therapy.
This is the most common type of radiation treatment in which the radiation is given from a machine outside the body. It can be used to treat large areas of the body, if necessary. The machine typically used to create the radiation beam is called a linear accelerator, or linac.Computers with special software are used to adjust the size and shape of the beam and to point it in the right direction to target the tumor while sparing the normal tissue surrounding the cancer cells.
External-beam radiation therapy does not make you radioactive.
Types of external-beam radiation therapy include the following:
Three-dimensional conformal radiation therapy (3D-CRT): This treatment uses special computers to create detailed three-dimensional pictures of the cancer. This allows the treatment team to aim the radiation more precisely, which means that they can use higher doses of radiation while reducing damage to healthy tissue. Studies have shown that 3D-CRT can lower the risk of complications.
Intensity modulated radiation therapy (IMRT): This treatment can better direct the radiation dose to the tumor than 3D-CRT by precisely modulating (varying) the intensity of the beam under strict computer guidance. (The positioning of the beam occurs during a specialized planning process.)
IMRT has been shown to allow higher doses of radiation while protecting normal tissues.
Proton beam therapy: This treatment uses protons, rather than x-rays, to treat some cancers. Protons are parts of atoms. They have enough energy to destroy cancer cells when they are directed to a particular site of cancer in the body while allowing better control of the radiation dose to nearby healthy tissue, reducing the damage to that tissue. Because this therapy is relatively new and requires highly specialized equipment, it is currently only available in certain medical centers across the country.
Stereotactic radiation therapy: This treatment delivers a large, precise radiation dose to a small tumor area. Because of the precision involved in this type of treatment, the patient must remain extremely still. Head frames or individual body molds may be used limit movement. Although stereotactic radiation therapy is often performed as a single treatment, some patients may need fractionated radiation therapy, which involves multiple treatments.
Internal radiation therapy.
Also known as brachytherapy, which means short-distance therapy, internal radiation therapy involves placing radioactive material into the cancer itself or into tissue surrounding it. These implants may be permanent or temporary and may require a hospital stay. Permanent implants are tiny steel seeds (capsules) about the size of a grain of rice that contain radioactive material and are placed inside the body at the tumor site. The seeds deliver most of the radiation around the area of the implant; however, some radiation can be emitted (sent) from the patient's body. This means that the patient needs to take certain precautions to protect others from radiation exposure while the seeds are still active. (For more information, see the "Safety for the patient and family" section.) Over time, the implant loses its radioactivity, but the inactive seeds remain in the body. For temporary implants, the radiation is delivered through needles, catheters (tubes that carry fluid in or out of the body), or specialized applicators and kept in the body for a specific time, from a few minutes to a few days. When the temporary radiation is kept for more than a few minutes, the patient is stationed in a private room while the implants are in place to limit others' exposure to the radiation.
Other treatment options
Intraoperative radiation therapy (IORT).
Radiation therapy can be delivered directly to the tumor during surgery, either as external-beam radiation therapy or as internal radiation therapy. This technique allows the surgeon to move normal tissue out of the way before radiation therapy occurs, and it may be helpful when healthy, vital (life-sustaining) organs are dangerously close to the tumor.
Systemic radiation therapy.
Systemic (whole body) radiation therapy uses radioactive materials, such as iodine 131 or strontium 89, that can be taken by mouth or injected into the body to target cancer cells. These radioactive materials can leave the body through saliva, sweat, and urine, making these fluids radioactive. Additional safety measures must be used to protect people who come in close contact with the patient. For more information, see the "Safety for the patient and family" section.
Radioimmunotherapy.
A type of systemic therapy, this treatment uses monoclonal antibodies (man-made versions of naturally occurring proteins that find and attack things in the body that the immune system identifies as invaders) that can bind (stick) to some types of cancer cells while leaving normal cells alone. By attaching radioactive molecules to these antibodies in a laboratory, they can deliver doses of radiation directly to the tumor. Examples of these radioactive molecules include ibritumomab (Zevalin) and tositumomab (Bexxar).
Radiosensitizers and radioprotectors.
Researchers are studying radiosensitizing and radioprotectant substances that help radiation better destroy tumors or better protect normal tissues near the area being treated. Examples of radiosensitizers include fluorouracil (5-FU) and cisplatin (Platinol). Meanwhile,amifostine (Ethyol) is a radioprotector.
Safety for the patient and family
When receiving external-beam radiation therapy, the patient does not become radioactive; the radiation remains in the treatment room. However, with internal radiation therapy, a number of safety measures are necessary.
While the implant is in place, women who are pregnant and children younger than 18 should not visit.
Other visitors should sit at least 6 feet from the patient's bed and limit their stay to 30 minutes or fewer each day. Permanent implants remain radioactive after the patient is discharged from the hospital, and he or she should refrain from close (less than 6 feet) or lengthy (more than 5 minutes) contact with women who are pregnant and children for two months.
With systemic radiation therapy, safety precautions must be followed for the first few days after treatment. The risk of radiation exposure to family and friends can be minimized using the following precautions.
Maintaining personal hygiene following toilet use
Using separate utensils and towels
Drinking plenty of fluids to flush the remaining radioactive material from the body
Avoiding sexual contact
Minimizing contact with infants, children, and women who are pregnant
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