Most people think of radiation therapy as coming from a machine outside of the body, but there are actually several ways radiation therapy can be delivered. Sometimes radiation is given more than one way at the same time, or different types of radiation may be given one after the other.

External beam radiation

External beam radiation is the most widely used type of radiation therapy. The radiation comes from a machine outside the body and is focused on the area affected by the cancer. It is much like getting an x-ray, but for a longer time. This type of radiation is most often given by machines called linear accelerators.

The radiation is aimed at the tumor but also affects the normal tissue it passes through on its way into and out of the body. External beam radiation allows large areas of the body to be treated and allows treatment of more than one area, such as the main tumor and nearby lymph nodes. External radiation is usually given in daily treatments over several weeks. It is given in an outpatient clinic or treatment center, so you do not have to stay in the hospital.

Some newer types of external beam radiation are making radiation therapy safer and more effective. These are described in the section. "What's new in radiation therapy?"

Treatment planning for external beam radiation

The process of planning external beam radiation therapy involves many steps and may take several days to complete. But it is one of the key parts of your radiation treatment. The doctor will design a treatment just for you. The treatment will give the strongest dose of radiation to the cancer but will spare normal tissue as much as possible. This will help reduce any side effects you might have.

The first part of treatment planning is called simulation. It is sometimes referred to as a "marking session." You will be asked to lie still on a table while the health care team works out the best treatment position for you. They will then mark the radiation field (also called the treatment port), which is the exact place on your body where the beam of radiation will be aimed. Your doctor may use imaging tests such as a CT scan to check the size of the tumor, figure out where it is more likely to spread, outline normal tissues that are in the treatment area, take measurements, and develop the treatment plan.

Through a complex process called dosimetry, computer programs are used to find out how much radiation the nearby normal structures would be exposed to in order to deliver the prescribed dose to the cancer.

The doctor and dosimetrist will work together to decide on the amount of radiation you will get and the best ways to aim it at the cancer. They base this on the size of the tumor, how sensitive the tumor is to radiation, and how well the normal tissue in the area can withstand the radiation.

Dosing and treatment for external beam radiation

The total amount of radiation you will get is measured in units called Gray (Gy). Often the dose is expressed in centigray (cGy), which is one hundredth of one Gray. For external radiation, the total dose is often divided into several smaller doses (called fractions) that are most often given over a number of weeks. This allows the best dose to be given with the least damage to normal tissues. In most cases, treatments are given 5 days a week, for about 5 to 8 weeks.

For some cancers, patients may be treated more often than once a day.

• Hyperfractionated radiation is when the daily dose is divided into 2 treatment sessions, without changing the length of the treatment. In this case, you would be treated twice a day for several weeks.

• Accelerated radiation is when the total dose of radiation is given over a shorter period of time by giving the same dose of radiation more frequently (more than once a day).

These types of schedule can make the radiation work better for some tumors. The down side is that radiation side effects are seen earlier and may be worse.

It is important that you are treated in exactly the same way each time so the right amount of radiation will be given to the right area. For external radiation, small, long-lasting or permanent (tattoo) marks may be put on your skin to show where treatment is to be focused. You will need to stay very still and in the same position during each treatment, which can last up to 30 minutes. Sometimes a special mold or cast of the body part to be treated will be used to hold you in a certain position. This helps make sure you're in the right place and helps you stay still. Your health care team may also need to make special blocks or shields to protect certain parts of your body from radiation during treatment.

Internal radiation therapy (brachytherapy)

Internal radiation therapy is also known as brachytherapy (brake-ee-THER-uh-pee), which means short-distance therapy. With this method, radioactive containers are placed into the tumor or into a body cavity close to the tumor. The advantage of brachytherapy is the ability to deliver a high dose of radiation to a small area. It is useful in cases that need a high dose of radiation or a dose that would be more than the normal tissues could stand if it had to come in from the outside. The main types of internal radiation are:

• interstitial radiation: the radiation source is placed directly into or next to the tumor using small pellets, seeds, wires, tubes, or containers.

• intracavitary radiation: a container of radioactive material is placed in a cavity of the body such as the chest, rectum, uterus, or vagina.

Ultrasound, x-rays, or CT scans are used to help the doctor put the radioactive source in the right place. The placement can be permanent (long-term) or temporary (short-term):

Permanent brachytherapy involves using small containers, called pellets or seeds, which are about the size of a grain of rice. They are put right into the tumors using thin, hollow needles. Once in place, the pellets give off radiation for several weeks or months. Because they are very small and cause little discomfort, they are simply left in place after their radioactive material is used up.

Temporary brachytherapy can be high-dose rate (HDR) or low-dose rate (LDR). Either type involves briefly placing hollow needles, tubes, or fluid-filled balloons into the area to be treated. Radioactive material can be put in these containers for a short period of time and then removed. For HDR brachytherapy, the radiation source is put into place for about 10 to 20 minutes at a time, and then removed. This process may be repeated twice a day over the course of a few days, or once a week for a few weeks. For LDR brachytherapy, the radiation source stays in place for up to 7 days. To keep the implant from moving out of place, you will need to stay in bed and lie fairly still. For this reason, you will be kept in the hospital during LDR therapy.

Treatment with internal radiation

Severe pain or illness is not likely to happen during implant therapy. You may feel sleepy, weak, or nauseated for a short time because of the anesthesia (drugs used to make you sleepy) while the implant is put in place. Tell the nurse if you have any unusual side effects such as burning or sweating.

Anesthesia is usually not needed to take out the implant. Most can be taken out right in your hospital room. If you had to stay in bed during implant therapy, you might have to stay in the hospital an extra day or so after the implant is removed.

Once the implant is removed, there is no radioactivity in your body. The doctor will tell you if you should limit your physical activity for a time. Most patients are encouraged to do as much as they feel like. Some people need extra sleep or rest breaks during their first days at home, but you will probably feel stronger quickly. The area that has been treated with an implant may be sore or sensitive for some time after treatment.

Radiopharmaceuticals

Radiopharmaceuticals are drugs containing radioactive materials. They may be put into a vein, taken by mouth, or placed in a body cavity. Depending on the drug and how it is given, these materials travel to various parts of the body to treat cancer or relieve its symptoms.

Treatment of bone pain

Strontium 89 and samarium 153 are radiopharmaceuticals often used for tumors that have spread to the bones (bone metastases). Other drugs are now under study as well. These medicines are given by vein (intravenously or IV), so that they go into circulation with the blood. They build up in the areas of the bone where there is cancer. The radiation they give off kills cancer cells and eases the pain caused by bone metastases.

For cancer that has already spread to more than one bone, this approach is much better than trying to aim external beam radiation at each affected bone. These drugs may also be used along with external beam radiation which is aimed at the most painful bone metastases. This combined approach has helped many men with prostate cancer, but its use for other cancers has not been studied as much.

Some people notice an increase in bone pain for the first day or 2 after treatment. These drugs can also lower blood cell counts, especially white blood cells (this can increase the risk of infection) and platelets (which can raise the risk of bruising or bleeding).

Treatment of thyroid cancer

The thyroid gland absorbs nearly all of the iodine in the blood. Because of this, radioactive iodine (also known as radioiodine or iodine 131) can be used to destroy the thyroid gland and thyroid cancer with little effect on the rest of the body. This treatment is often used after thyroid cancer surgery to destroy any thyroid cells that may have been left behind or to treat some types of thyroid cancer that spread to lymph nodes and other parts of the body. For more information, please see our document, Thyroid Cancer.

Small doses of radioiodine can be given without having to admit the patient to the hospital, but the usual treatment doses for thyroid cancer require 2 to 3 days in the hospital. Several weeks after treatment, the radioiodine is gone from the body. At that point, doctors can check to see how well the treatment worked.

Short-term side effects of radioiodine treatment are rare, but may include neck tenderness, nausea and stomach irritation, tenderness of the salivary glands, and dry mouth. Large doses may cause low blood cell counts. Men may become infertile (unable to father children) after large doses.

There may be some longer-term risks too. Large studies have found that there may be a very slight increase in the risk of developing other types of cancer, including leukemia, in the future.

It is recommended that women of childbearing age avoid becoming pregnant for at least one year after treatment, even though there is no evidence of birth defects if a woman gets pregnant after the treatment.

Phosphorus 32

This form of phosphorus (also known as P-32 or chromic phosphate P 32) is put inside brain tumors that are cystic (hollow) to kill the tumor without hurting the healthy parts of the brain. In the past, P-32 was given into a vein (IV) as a common treatment for a blood disease called polycythemia vera. P-32 was also placed inside the abdomen (into the belly) as a treatment for ovarian cancer. It is rarely used in these ways today.

Radio-labeled antibodies

Monoclonal antibodies are man-made versions of immune system proteins that attack only a specific molecular target on certain cancer cells. Scientists have learned how to pair these antibodies with radioactive atoms. When put into the bloodstream, the antibodies act as homing devices. They attach only to their target, bringing radiation directly to the cancer.

Radio-labeled antibodies are used to treat some non-Hodgkin lymphomas, especially those that don't respond to other treatments. They may cause allergic reactions when first infused. They may also lower blood cell counts, which can raise the risk of infections, and lower platelets causing bruising or bleeding.

Go back to Radiation Principles.

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