What is radiation therapy?
Radiation therapy is the use of a high-energy x-rays to destroy cancer cells and shrink tumors. Cancer cells reproduce faster than normal cells in the body. Radiation therapy targets these rapidly dividing cells. The radiation reacts with water in the cells, and this reaction damages the DNA or genetic material in the cell that controls cell growth. Most normal cells can recover from the effects of radiation and function properly. Cancer cells can’t repair themselves easily and they are destroyed. The goal of radiation therapy is to damage as many cancer cells as possible, while limiting harm to nearby healthy tissue.
There are different types of radiation and different ways to deliver the radiation. For example, certain types of radiation can penetrate more deeply into the body than can others. In addition, some types of radiation can be very finely controlled to treat only a small area (an inch of tissue, for example) without damaging nearby tissues and organs. Other types of radiation are better for treating larger areas.
In some cases, the goal of radiation treatment is the complete destruction of an entire tumor. In other cases, the aim is to shrink a tumor and relieve symptoms. In either case, doctors plan treatment to spare as much healthy tissue as possible.a
About half of all cancer patients receive some type of radiation therapy. Radiation therapy may be used alone or in combination with other cancer treatments, such as chemotherapy or surgery. In some cases, a patient may receive more than one type of radiation therapy.
When is radiation therapy used?
Radiation therapy may be used to treat almost every type of solid tumor, including cancers of the brain, breast, cervix, larynx, lung, pancreas, prostate, skin, spine, stomach, uterus, or soft tissue sarcomas. Radiation can also be used to treat leukemia and lymphoma (cancers of the blood-forming cells and lymphatic system, respectively). Radiation dose to each site depends on a number of factors, including the type of cancer and whether there are tissues and organs nearby that may be damaged by radiation.
For some types of cancer, radiation may be given to areas that do not have evidence of cancer. This is done to prevent cancer cells from growing in the area receiving the radiation. This technique is called prophylactic radiation therapy.
Radiation therapy also can be given to help reduce symptoms such as pain from cancer that has spread to the bones or other parts of the body. This is called palliative radiation therapy.
What is the difference between external radiation and internal radiation?
The type of radiation to be given depends on the type of cancer, its location, how far into the body the radiation will need to go, the patient’s general health and medical history, whether the patient will have other types of cancer treatment, and other factors.
Most people who receive radiation therapy for cancer have external radiation, but some patients will receive both external and interal radiation therapy. External radiation therapy usually is given on an outpatient basis and is used to treat most types of cancer, including cancer of the bladder, brain, breast, cervix, larynx, lung, prostate, and vagina. In addition, external radiation may be used to relieve pain or ease other problems when cancer spreads to other parts of the body from the primary site.
What are the sources of energy for external radiation therapy?
The energy (source of radiation) used in external radiation therapy is generated by a machine called a linear accelerator. Depending on the amount of energy the x-rays have, they can be used to destroy cancer cells on the surface of the body (lower energy) or deeper into tissues and organs (higher energy). The machine is normally the size of a small room measuring 10 feet high and 15 feet long. Treatment begins by having the patient lie down on a movable treatment couch while the linear accelerator delivers beams of radiation to the tumor from multiple directions or angles. Lasers are used to make sure the patient is in the proper position. The intensity of each beam’s radiation dose can be varied according to the patient’s treatment plan.
To ensure patient safety at the June E. Nylen Cancer Center, several safety systems are built into the linear accelerator so that it will deliver the prescribed dose intended by the Radiation Oncologist. During treatment, the radiation therapist continuously monitors the patient both visually and audibly.
Intensity-modulated radiation therapy (IMRT)
IMRT is an advanced mode of high precision radiation therapy that uses computer controlled x-ray equipment (linear accelerator) and a multi-leaf collimator to deliver precise radiation beams to a targeted area. The multi-leaf collimator is a device with a series of computer-controlled “shutters” that subdivide (modulate) radiation beams into many beamlets aimed in various directions. The equipment can be rotated around the patient so that radiation beams can be sent from the best angles. The beams conform as closely as possible to the shape of the tumor. By varying the intensities of the beams, different doses of radiation are delivered to small areas of tissues at the same time. This technology allows for the delivery of higher doses of radiation within the tumor and lower doses to normal tissue. Because IMRT equipment is highly specialized, not every cancer treatment center offers IMRT. June E. Nylen Cancer Center has a strong and ongoing commitment to bringing our patients the best and most current therapies,
How does the doctor measure the dose of radiation?
The amount of radiation absorbed by the tissues is called the radiation dose. Different tissues can tolerate various amounts of radiation. For example, the liver can receive a much higher dose than the kidneys. The total dose of radiation is usually divided into smaller doses that are given daily over a specific time period. This maximizes the destruction of cancer cells while minimizing the damage to healthy tissue.
Will radiation therapy make the patient radioactive?
Cancer patients receiving radiation therapy are often concerned that the treatment will make them radioactive. The answer to this question depends on the type of radiation therapy being given.
External radiation therapy will not make the patient radioactive. Patients do not need to avoid being around other people because of the treatment.
Internal radiation therapy that involves sealed implants emits radioactivity, so a stay in the hospital may be needed. Certain precautions are taken to protect hospital staff and visitors. The sealed sources deliver most of their radiation mainly around the area of the implant, so while the area around the implant is radioactive, the patient’s whole body is not radioactive.
Who plans and delivers the radiation treatment to the patient?
Many health care providers help to plan and deliver radiation treatment to the patient. The radiation therapy team includes the radiation oncologist, a doctor who specializes in using radiation to treat cancer; the dosimetrist, who determines the proper radiation dose; the radiation physicist, who makes sure that the machine delivers the right amount of radiation to the correct site in the body; and the radiation therapist, who gives the radiation treatment. Often, radiation treatment is only one part of the patient’s total therapy. Combined modality therapy, the use of radiation with drug therapy, is commonly used.
The radiation oncologist also works with the medical or pediatric oncologist, surgeon, radiologist (a doctor who specializes in creating and interpreting pictures of areas inside the body), pathologist (a doctor who identifies diseases by studying cells and tissues under a microscope), and others to plan the patient’s total course of therapy. A close working relationship between the radiation oncologist, medical or pediatric oncologist, surgeon, radiologist, and pathologist is important in planning the total therapy.
What is treatment planning, and why is it important?
Because there are so many types of radiation and many ways to deliver it, treatment planning is a very important first step for every patient who will have radiation therapy. Before radiation therapy is given, the patient’s radiation therapy team determines the amount and type of radiation the patient will receive.
If the patient will have external radiation, the radiation oncologist uses a process called simulation to define where to aim the radiation. During simulation, the patient lies very still on an examining table while the radiation therapist uses a special x-ray machine to define the treatment port or field—the exact place on the body where the radiation will be aimed. Most patients have more than one treatment port. Simulation may also involve CT scans or other imaging studies to help the radiation therapist plan how to direct the radiation. The simulation may result in some changes to the treatment plan so that the greatest possible amount of healthy tissue can be spared from receiving radiation. The simulation visit is an key part of treatment; the visit may take several hours, but treatment is not given that day.
The areas to receive radiation are marked with either a temporary or permanent marker, tiny dots or a “tattoo” showing where the radiation should be aimed. These marks are also used to determine the exact site of the initial treatments if the patient should need radiation treatment later.
Depending on the type of radiation treatment, the radiation therapist may make body molds or other devices that keep the patient from moving during treatment. These are usually made from foam, plastic, or plaster. In some cases, the therapist will also make shields that cannot be penetrated by radiation to protect organs and tissues near the treatment field.
When the simulation is complete, the radiation therapy team meets to decide how much radiation is needed (the dose of radiation), how it should be delivered, and how many treatments the patient should have.