During simulation and daily treatments, it is necessary to ensure that the patient will be in exactly the same position every day relative to the machine delivering the treatment or doing the imaging. Body molds, head masks, or other devices may be constructed for an individual patient to make it easier for a patient to stay still. Temporary skin marks and even tattoos are used to help with precise patient positioning.
After simulation, the radiation oncologist then determines the exact area that will be treated, the total radiation dose that will be delivered to the tumor, how much dose will be allowed for the normal tissues around the tumor, and the safest angles (paths) for radiation delivery.
The staff working with the radiation oncologist (including physicists and dosimetrists ) use sophisticated computers to design the details of the exact radiation plan that will be used. After approving the plan, the radiation oncologist authorizes the start of treatment. On the first day of treatment, and usually at least weekly after that, many checks are made to ensure that the treatments are being delivered exactly the way they were planned.
Radiation doses for cancer treatment are measured in a unit called a gray (Gy), which is a measure of the amount of radiation energy absorbed by 1 kilogram of human tissue. Different doses of radiation are needed to kill different types of cancer cells.
Radiation can damage some types of normal tissue more easily than others. For example, the reproductive organs ( testicles and ovaries ) are more sensitive to radiation than bones. The radiation oncologist takes all of this information into account during treatment planning.
If an area of the body has previously been treated with radiation therapy, a patient may not be able to have radiation therapy to that area a second time, depending on how much radiation was given during the initial treatment. If one area of the body has already received the maximum safe lifetime dose of radiation, another area might still be treated with radiation therapy if the distance between the two areas is large enough.
The area selected for treatment usually includes the whole tumor plus a small amount of normal tissue surrounding the tumor. The normal tissue is treated for two main reasons:
Radiation can come from a machine outside the body (external-beam radiation therapy) or from radioactive material placed in the body near cancer cells (internal radiation therapy, more commonly called brachytherapy). Systemic radiation therapy uses a radioactive substance, given by mouth or into a vein, that travels in the blood to tissues throughout the body.
The type of radiation therapy prescribed by a radiation oncologist depends on many factors, including:
External-beam radiation therapy
External-beam radiation therapy is most often delivered in the form of photon beams (either x-rays or gamma rays) ( 1 ). A photon is the basic unit of light and other forms of electromagnetic radiation . It can be thought of as a bundle of energy. The amount of energy in a photon can vary. For example, the photons in gamma rays have the highest energy, followed by the photons in x-rays.
Patients usually receive external-beam radiation therapy in daily treatment sessions over the course of several weeks (see Question 7 ). The number of treatment sessions depends on many factors, including the total radiation dose that will be given.
One of the most common types of external-beam radiation therapy is called 3-dimensional conformal radiation therapy (3D-CRT). 3D-CRT uses very sophisticated computer software and advanced treatment machines to deliver radiation to very precisely shaped target areas.
Many other methods of external-beam radiation therapy are currently being tested and used in cancer treatment. These methods include:
Patients can discuss these different methods of radiation therapy with their doctors to see if any is appropriate for their type of cancer and if it is available in their community or through a clinical trial (see Question 11 ).
Internal radiation therapy
Internal radiation therapy (brachytherapy) is radiation delivered from radiation sources (radioactive materials) placed inside or on the body ( 12 ). Several brachytherapy techniques are used in cancer treatment. Interstitial brachytherapy uses a radiation source placed within tumor tissue, such as within a prostate tumor. Intracavitary brachytherapy uses a source placed within a surgical cavity or a body cavity, such as the chest cavity, near a tumor. Episcleral brachytherapy, which is used to treat melanoma inside the eye, uses a source that is attached to the eye.
In brachytherapy, radioactive isotopes are sealed in tiny pellets or “seeds.” These seeds are placed in patients using delivery devices, such as needles, catheters , or some other type of carrier. As the isotopes decay naturally, they give off radiation that damages nearby cancer cells.
If left in place, after a few weeks or months, the isotopes decay completely and no longer give off radiation. The seeds will not cause harm if they are left in the body (see permanent brachytherapy, described below).
Brachytherapy can be given as a low- dose-rate or a high-dose-rate treatment:
Doctors can use brachytherapy alone or in addition to external-beam radiation therapy to provide a “boost” of radiation to a tumor while sparing surrounding normal tissue ( 12 ).
Systemic radiation therapy
In systemic radiation therapy, a patient swallows or receives an injection of a radioactive substance, such as radioactive iodine or a radioactive substance bound to a monoclonal antibody .
Radioactive iodine (131I) is a type of systemic radiation therapy commonly used to help treat some types of thyroid cancer . Thyroid cells naturally take up radioactive iodine.
For systemic radiation therapy for some other types of cancer, a monoclonal antibody helps target the radioactive substance to the right place. The antibody joined to the radioactive substance travels through the blood, locating and killing tumor cells. For example:
Many other systemic radiation therapy drugs are in clinical trials for different cancer types.
Some systemic radiation therapy drugs relieve pain from cancer that has spread to the bone (bone metastases). This is a type of palliative radiation therapy. The radioactive drugs samarium-153 -lexidronam (Quadramet®) and strontium-89 chloride (Metastron®) are examples of radiopharmaceuticals used to treat pain from bone metastases ( 13 ).
Patients who receive most types of external-beam radiation therapy usually have to travel to the hospital or an outpatient facility up to 5 days a week for several weeks. One dose (a single fraction) of the total planned dose of radiation is given each day. Occasionally, two treatments a day are given.
Most types of external-beam radiation therapy are given in once-daily fractions. There are two main reasons for once-daily treatment:
Researchers hope that different types of treatment fractionation may either be more effective than traditional fractionation or be as effective but more convenient.
A patient may receive radiation therapy before, during, or after surgery. Some patients may receive radiation therapy alone, without surgery or other treatments. Some patients may receive radiation therapy and chemotherapy at the same time. The timing of radiation therapy depends on the type of cancer being treated and the goal of treatment (cure or palliation).
Radiation therapy given before surgery is called pre-operative or neoadjuvant radiation. Neoadjuvant radiation may be given to shrink a tumor so it can be removed by surgery and be less likely to return after surgery ( 1 ).
Radiation therapy given during surgery is called intraoperative radiation therapy (IORT). IORT can be external-beam radiation therapy (with photons or electrons) or brachytherapy. When radiation is given during surgery, nearby normal tissues can be physically shielded from radiation exposure ( 15 ). IORT is sometimes used when normal structures are too close to a tumor to allow the use of external-beam radiation therapy.
Radiation therapy given after surgery is called post-operative or adjuvant radiation therapy.
Radiation therapy given after some types of complicated surgery (especially in the abdomen or pelvis) may produce too many side effects; therefore, it may be safer if given before surgery in these cases ( 1 ).
The combination of chemotherapy and radiation therapy given at the same time is sometimes called chemoradiation or radiochemotherapy. For some types of cancer, the combination of chemotherapy and radiation therapy may kill more cancer cells (increasing the likelihood of a cure), but it can also cause more side effects ( 1 , 14 ).
After cancer treatment, patients receive regular follow-up care from their oncologists to monitor their health and to check for possible cancer recurrence. Detailed information about follow-up care can be found in the National Cancer Institute fact sheet Follow-up Care After Cancer Treatment, which is available at http://www.cancer.gov/cancertopics/factsheet/therapy/followup on the Internet.
External-beam radiation does not make a patient radioactive.
During temporary brachytherapy treatments, while the radioactive material is inside the body, the patient is radioactive; however, as soon as the material is removed, the patient is no longer radioactive. For temporary brachytherapy, the patient will usually stay in the hospital in a special room that shields other people from the radiation.
During permanent brachytherapy, the implanted material will be radioactive for several days, weeks, or months after the radiation source is put in place. During this time, the patient is radioactive. However, the amount of radiation reaching the surface of the skin is usually very low. Nonetheless, this radiation can be detected by radiation monitors and contact with pregnant woman and young children may be restricted for a few days or weeks.
Some types of systemic radiation therapy may temporarily make a patient’s bodily fluids (such as saliva, urine, sweat, or stool) emit a low level of radiation. Patients receiving systemic radiation therapy may need to limit their contact with other people during this time, and especially avoid contact with children younger than 18 and pregnant women.
A patient’s doctor or nurse will provide more information to family members and caretakers if any of these special precautions are needed. Over time (usually days or weeks), the radioactive material retained within the body will break down so that no radiation can be measured outside the patient’s body.
Radiation therapy can cause both early ( acute ) and late ( chronic ) side effects. Acute side effects occur during treatment, and chronic side effects occur months or even years after treatment ends ( 1 ). The side effects that develop depend on the area of the body being treated, the dose given per day, the total dose given, the patient’s general medical condition, and other treatments given at the same time.
Acute radiation side effects are caused by damage to rapidly dividing normal cells in the area being treated. These effects include skin irritation or damage at regions exposed to the radiation beams. Examples include damage to the salivary glands or hair loss when the head or neck area is treated, or urinary problems when the lower abdomen is treated.
Most acute effects disappear after treatment ends, though some (like salivary gland damage) can be permanent. The drug amifostine (Ethyol®) can help protect the salivary glands from radiation damage if it is given during treatment. Amifostine is the only drug approved by the FDA to protect normal tissues from radiation during treatment. This type of drug is called a radioprotector. Other potential radioprotectors are being tested in clinical trials (see Question 11 ).
Fatigue is a common side effect of radiation therapy regardless of which part of the body is treated. Nausea with or without vomiting is common when the abdomen is treated and occurs sometimes when the brain is treated. Medications are available to help prevent or treat nausea and vomiting during treatment.
Late side effects of radiation therapy may or may not occur. Depending on the area of the body treated, late side effects can include ( 1 ):
Second cancers that develop after radiation therapy depend on the part of the body that was treated ( 16 ). For example, girls treated with radiation to the chest for Hodgkin lymphoma have an increased risk of developing breast cancer later in life. In general, the lifetime risk of a second cancer is highest in people treated for cancer as children or adolescents ( 16 ).
Whether or not a patient experiences late side effects depends on other aspects of their cancer treatment in addition to radiation therapy, as well as their individual risk factors . Some chemotherapy drugs, genetic risk factors, and lifestyle factors (such as smoking) can also increase the risk of late side effects.
When suggesting radiation therapy as part of a patient’s cancer treatment, the radiation oncologist will carefully weigh the known risks of treatment against the potential benefits for each patient (including relief of symptoms, shrinking a tumor, or potential cure). The results of hundreds of clinical trials and doctors’ individual experiences help radiation oncologists decide which patients are likely to benefit from radiation therapy.
A more comprehensive discussion of acute and late side effects from radiation therapy, as well as ways to cope with these side effects, can be found in the NCI publications Radiation Therapy and You: Support for People With Cancer ( http://www.cancer.gov/cancertopics/radiation-therapy-and-you ) and the Radiation Therapy Side Effects Fact Sheets ( http://www.cancer.gov/cancertopics/wtk/index ).
Doctors and other scientists are conducting research studies called clinical trials to learn how to use radiation therapy to treat cancer more safely and effectively. Clinical trials allow researchers to examine the effectiveness of new treatments in comparison with standard ones, as well as to compare the side effects of the treatments.
Researchers are working on improving image-guided radiation so that it provides real-time imaging of the tumor target during treatment. Real-time imaging could help compensate for normal movement of the internal organs from breathing and for changes in tumor size during treatment.
Researchers are also studying radiosensitizers and radioprotectors, chemicals that modify a cell's response to radiation:
The use of carbon ion beams in radiation therapy is being investigated by researchers, but, at this time, the use of these beams remains experimental. Carbon ion beams are available at only a few medical centers around the world. They are not currently available in the United States. Researchers hope that carbon ion beams may be effective in treating some tumors that are resistant to traditional radiation therapy.
People with cancer who are interested in taking part in a clinical trial should talk with their doctor. A comprehensive list of current clinical trials is available on NCI’s Web site at http://www.cancer.gov/clinicaltrials on the Internet.
NCI's Cancer Information Service (CIS) can also provide information about clinical trials and help with clinical trial searches. Call the CIS at 1–800–4–CANCER (1–800–422–6237).
Related NCI materials and Web pages:
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