Radiation therapy
is the use of penetrating beams of high-energy waves or streams of particles called radiation to treat disease. Radiation has been used to treat cancer since the late 19th century. In fact, the first successful radiation treatment for cancer was reported in 1898.
In its earliest state, radiation was given in single, large doses, which caused many complications. By 1940, doctors had begun dividing the total dose of radiation into several smaller doses. This process is known as fractionation of the dose. Fractionation is very important because it allows the oncologist to destroy tumor cells, while allowing normal tissues to repair the radiation damage.
In the last 50 years, technology has allowed for great advances in radiation therapy, including deeper penetration of the radiation and less scatter to healthy tissues. Currently, there exists a delicate balance between using radiation to treat cancer cells and minimizing its adverse side effects on the body's normal cells.
Radiation therapy destroys the ability of cancer cells to grow and divide. When high-energy ionizing radiation is given as cancer therapy, some cells are directly damaged, but more cells are indirectly affected by the radiation. The rays or particles enter the cell's nucleus, interact with water present in the nucleus, and form a free radical called hydroxyl radical. The hydroxyl radical is unstable and causes damage to the cell's DNA. Due to this damage, some cells die immediately. Some cells will survive in the short-term, but are unable to divide and will die at the time of mitosis, or cell division.
Normal, healthy tissues are affected by radiation therapy as well, and this accounts for the adverse side effects seen with this type of treatment. To help minimize side effects, radiation is divided into doses and spread out over time. In addition, radiation is targeted as much as possible to shield normal tissue and only irradiate the cancer cells.
Unlike
chemotherapy, which is a systemic treatment, radiation therapy is a localized treatment. This means it affects only the cells in the specific areas of the body where the radiation is directed. Radiation therapy is sometimes used in combination with other therapies, like chemotherapy or hormonal therapy, to help improve treatment results. Also, radiation therapy can be given before, during, or after surgery.
Radiation therapy is given with the intention of completely destroying the disease. When this is not possible, controlling the growth and spread of the cancer is the goal. In addition, improving quality of life by controlling symptoms associated with cancer is an aim of radiation therapy. These symptoms include pain, uncontrolled bleeding, tumor obstruction around major blood vessels and organs, and spinal cord compression.
Determining if your cancer may be appropriately treated by radiation therapy is based on several factors, such as tumor type, location, size, and response to other modalities including surgery and chemotherapy. Your radiation oncologist is the only medical professional qualified to give an absolute opinion on the role of radiation therapy in the management of your disease.
Some factors affecting how well radiation therapy will work include the following:
- Phase of cell—A cell goes through five phases in its cycle of division—from resting to mitosis. Cells in the resting phase are less sensitive to radiation (and therefore less likely to be damaged) than cells that are actually dividing (in mitosis).
- Division rate of the cell—Rapidly dividing cells are more sensitive than slowly dividing cells.
-
Oxygenation—Because oxygen is necessary to form the hydroxyl radical (which leads to cell destruction), highly oxygenated tissues are more sensitive to radiation therapy. This has been clearly demonstrated in
cervical cancers
and cancers of the head and neck. In fact, the presence of oxygen is so important that patients who smoke, and therefore lower the oxygen level to their tumor, suffer from a 50% reduction in the ability of the radiation to kill the cancer.
In external radiation therapy, rays are directed at the tumor from outside the body. Prior to treatment, your doctor will develop a plan to determine the best method for delivering treatment. In a process called simulation, you will be asked to lie on the examination table while the radiation therapist uses a special x-ray machine to define the area of treatment. Radiographic studies, like a
CT scan, an
MRI, or a
barium enema, help the physician visualize the exact area that needs treatment. Using this information, the doctor can calculate the maximum radiation dose to the tumor, while minimizing the dose to the normal surrounding tissues.
A CT scan is a type of x-ray that uses a computer to produce cross-sectional images of the inside of the body. An MRI scan uses magnetic waves to produce images of the inside of the body. Using a large magnet, radio waves, and a computer, an MRI produces 2D and 3D pictures. A barium enema is a rectal injection of barium, a substance that coats the lining of the colon and rectum. It is done before x-rays are taken in order to create better x-ray images.
If you receive external radiation therapy, you will go to the hospital or clinic each day for treatment. Usually, treatments are given 5 days a week for 2 to 8 weeks. The total dose of radiation and the number of treatments necessary will depend on the size, location, and type of cancer you have, as well as your general health and other medical treatments you may be having. This procedure is like having an x-ray. Actual treatment time (the time you are receiving radiation) ranges from 2 to 5 minutes.
Radiation is usually given once a day with a dose based on the type and location of the tumor. In hyperfractionated radiation therapy, the daily dose is divided into smaller doses and given several times a day (usually twice a day). Treatments are separated by 4 to 6 hours.
Hyperfractionation is used in the treatment of head and neck cancers, some
lung cancers, and in a situation where a patient has already had radiation therapy and needs more to that same area. Other cancer sites have not been conclusively shown to respond to radiation given more often than once daily.
Different types of machines are used to deliver the radiation. The higher the energy produced by the machine, the greater the depth of penetration. In addition, there is less radiation scatter with higher energies.
This table explains the two main types of treatment machines.| Machine | Treatment Beam | Characteristics | Use |
|---|
| Orthovoltage | X-rays with 150-500 kilovolts (kV) of energy |
Low-level energy
Superficial treatment scatter of radiation beam
|
Superficial
skin cancer |
|---|
| Megavoltage | X-rays and electrons with
1-18 million volts of energy |
Deeper penetration below skin level
Less scatter
| All tumors other than skin cancer |
|---|
At the end of the treatment regimen, the tumor site often gets an extra dose of radiation, called a boost.
Internal radiation therapy, also called brachytherapy, places the radiation source as close as possible to the cancer cells. Radioactive material, sealed in a thin wire, catheter, or tube, is placed directly into the affected tissue. This method concentrates the radiation on the cancer cells and minimizes the radiation damage to the normal tissue nearby.
The radioactive substances used for internal radiation therapy include the following:
- Cesium
- Iridium
- Iodine
- Phosphorus
- Palladium
The type of implant and how it is placed depends on the size and location of the tumor. Methods include the following:
- Interstitial radiation—The implant is placed directly into the tumor via catheters, seeds, or capsules. This is commonly used for prostate cancer.
- Intracavitary radiation—Commonly used for cervical cancer, the implant is placed in special applicators inside a body cavity.
-
Intraluminal radiation—Commonly used for lung or
esophageal cancer, the implant is placed in special applicators inside a body passage or lumen.
- Surface brachytherapy—The implant is placed in or against the tumor. This is commonly used for skin cancer or melanoma of the eye.
Implants may be removed after a short time or left in place permanently. When left in place, the implants become non-radioactive in a short time. For the placement of most types of implants, you will need to be in the hospital.
Indications for internal radiation therapy include cancers of the head and neck, lung, breast, uterus, thyroid, cervix, rectum, bladder, and prostate. It is sometimes given in combination with external radiation therapy.
Intraoperative radiation combines
surgery
and radiation therapy. During surgery, after as much of the tumor as possible is removed, a large dose of radiation is given directly to the tumor bed and nearby areas. This therapy is sometimes given in combination with external radiation therapy.
Intraoperative radiation is used to treat locally advanced abdominal cancers such as stomach, pancreatic, colorectal, and retroperitoneal sarcomas.
In photodynamic therapy (PDT), photosensitizers, or light-sensitive molecules, are injected into the bloodstream and absorbed by cells throughout the body. These agents remain in cancer cells longer than in normal cells. When the cancer cells are exposed to laser light, the photosensitizers are activated and form oxygen radicals that affect cell membranes, the cytoplasm, and the DNA. This results in cell damage and death. PDT causes minimal damage to healthy tissue, but the laser light used in PDT cannot pass through more than 3 centimeters of tissue.
PDT is mainly used to treat tumors on or just under the skin or on the lining of internal organs. Currently, PDT is used in the treatment of skin, lung, and esophageal cancers as well as superficial cancers of the bladder, head, and neck.
In addition, PDT is used for
bone marrow purging. Bone marrow used for autologous transplantation must be relatively free of cancer cells. Before transplantation, the harvested marrow is often treated with PDT in a process known as "purging" to get rid of cancer cells.
In hyperthermia, body tissues are exposed to high temperatures (up to 106°F) to damage and kill cancer cells or to make cancer cells more sensitive to the effects of radiation. Methods include the following:
Local hyperthermia
—Heat is applied to a small area, usually the tumor itself, either externally or internally. If heated externally, high-frequency sound waves are aimed at the tumor using a device (like an ultrasound machine) outside the body. Internal heating can be done by inserting sterile probes that are either heated or filled with warm water, implanted microwave antennae, or radiofrequency electrodes.
Regional hyperthermia
—Heat is applied to an organ or a limb. This can be done with magnets or other devices that produce high energy. Or, blood can be removed, heated, and returned to the affected region.
Whole-body hyperthermia
—Heat is applied to the entire body. This is used for metastatic cancer that has spread throughout the body. Warm-water blankets, hot wax, inductive coils, or thermal chambers are used to raise body temperature.
Radiation therapy affects normal, healthy cells as well as cancer cells. When radiation is targeted at a cancerous site, there is destruction of normal tissue, in addition to cancer cells, in that area. A majority of the adverse effects are due to this phenomenon. The following are general side effects that can occur with radiation therapy.
Fatigue, or feeling tired, can be a symptom of the cancer itself, as well as a side effect of cancer treatment. It is experienced by many people receiving radiation therapy. The exact cause is not know, but it may result from a combination of lowered red blood cell counts, lack of sleep, pain, and poor appetite. Fatigue many occur after treatment each day and become chronic as treatment continues. Fatigue is not a life-threatening side effect, but it can be disruptive to daily life.
The level of fatigue varies among people, but generally, most people are able to continue work and light activities. To help combat fatigue, try not to do too much. If you start to feel tired, limit your activities. Try to get enough rest at night and take naps or short breaks throughout the day. Allow people to help you with daily responsibilities, like shopping, house cleaning, and child care.
Some people have found that light exercise, such as walking, helps combat fatigue. Talk with your doctor about how much exercise is right for you both during and after radiation therapy.
Skin reactions are normal and expected with radiation therapy. Reactions can occur as soon as 2 weeks into treatment. The skin becomes red and irritated and slight swelling may appear. After a few weeks of treatment, skin may become very dry, itchy, and flaky. In some types of radiation therapy, skin may develop a moist reaction. The skin starts to shed, leaving a raw, painful area. If this occurs, it is important to let your doctor know.
Skin reactions are more common in areas receiving large doses of radiation. Also, certain areas of the skin are more sensitive, such as facial skin, skin over bony prominences, and skin with a pre-existing surgical wound. When radiation therapy is used along with chemotherapy, there is a higher risk of developing a skin reaction. Most skin reactions disappear a few weeks after treatment is completed.
The following suggestions may help you avoid skin problems:
- Wash with lukewarm water and mild soap, and pat dry.
- Do not wear tight clothing over the area.
- Do not rub, scratch, or scrub the skin in the treated area.
- Avoid putting anything hot or cold on the treated area.
- Avoid exposing the radiated area to the sun during treatment.
- Ask your doctor to recommend a cleanser and moisturizer for your sensitive skin.
If large areas of active bone marrow are treated with radiation therapy, a decrease in bone marrow function occurs. Such treatment areas include the pelvis, spine, sternum, ribs, long bones, and skull. This can lead to low levels of red blood cells (
anemia), white blood cells (neutropenia), and platelets (thrombocytopenia). Resulting complications may include fatigue, serious infection, and uncontrolled bleeding.
During radiation therapy, blood levels may be monitored, particularly if chemotherapy is also being delivered, or if a large part of the body is being irradiated. For many sites treated with radiation, there is no reason to get blood samples, unless you begin to feel poorly and the doctor wants to determine if low blood counts are to blame. If a blood test shows significant bone marrow effects, your doctor may wait until your blood counts increase before continuing treatment. Blood transfusions are sometimes necessary.
Radiation therapy can cause hair loss, also known as
alopecia. Hair loss occurs only in the area being treated with radiation. If you receive radiation to your head, you may lose some or all of the hair on your scalp. The amount of hair that grows back depends on how much and what kind of radiation you received. Some people find that when their hair grows back, the color or texture may be slightly different.
Although not life-threatening, hair loss can be upsetting. Many people buy a wig or hairpiece, or use hats or scarves, to cover their heads. If you buy a wig because of cancer treatment, it is a tax-deductible expense and may be covered in part by health insurance.
Loss of appetite can be a symptom of the cancer itself, as well as a side effect of cancer treatment. It is not unusual to lose one or two pounds a week during radiation treatment. You will be weighed weekly to monitor your weight.
Many small meals, rather than three large ones, can help make eating seem less overwhelming. Ask your doctor for a referral to a registered dietitian (RD) to assist you in setting up a diet plan that helps you maintain weight. In addition, medications to increase your appetite are available. If it is painful to chew and swallow, you may want to try a powdered or liquid diet supplement. It is crucial that you get enough calories and protein so that your body has enough energy to fight the cancer. Studies have found that people who eat well cope better with their cancer and its treatment.
