Radiation Therapy
What is Radiation Therapy?
X-rays, gamma rays, and charged particles are types of radiation used for cancer treatment.
Radiation therapy uses precisely targeted X-rays to shrink and destroy cancer cells so they cannot multiply. Radiation therapy can be used to treat primary cancers or advanced cancers in many sites of the body. It may be the only treatment used, or used in combination with surgery and/or chemotherapy. It can also be used to reduce the size of the cancer and relieve pain, discomfort or other symptoms.
The radiation may be delivered by a machine outside the body (external-beam radiation therapy), or it may come from radioactive material placed in the body near cancer cells (internal radiation therapy, also called brachytherapy).
Systemic radiation therapy uses radioactive substances, such as radioactive iodine, that travel in the blood to kill cancer cells.
The length of treatment can vary depending on factors such as the location, type and stage of the cancer, and whether or not the radiotherapy is combined with other treatments, such as chemotherapy or surgery.
About half of all cancer patients receive some form of radiation therapy sometime during the course of their treatment.
Why is Radiation Therapy given?
Radiation therapy may aim to:
- Cure.
- Some cancers can be cured by radiation therapy alone or combined with other treatments.
- Control.
- Radiation therapy can control some cancers by making them smaller or stopping them from spreading.
- Relieve symptoms.
- If a cure is not possible, radiation therapy may be used to reduce cancer symptoms and prolong a good quality of life.
What are the potential side effects of radiation therapy?
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. 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.
Side-effects vary and will depend on which area of your body is being treated. Possible side-effects include:
- fatigue (tiredness)
- dry, red or itchy skin
- swelling
- loss of appetite
- nausea (feeling sick)
- digestive problems
- dry or sore throat or mouth
- cough or shortness of breath.
Most side-effects can be managed and will gradually disappear once the treatment has finished.
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| Possible Side Effects of Radiation Therapy |
Does radiation therapy kill only cancer cells?
No, radiation therapy can also damage normal cells, leading to side effects.
The potential damage to normal cells are taken into account by doctors when planning a patient’s course of radiation therapy. The amount of radiation that normal tissue can safely receive is known for all parts of the body. This information is used by doctors to assist them in deciding where to aim radiation during treatment.
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| Cancer Cells During Radiation Therapy |
How does radiation therapy kill cancer cells?
Radiation therapy kills cancer cells by damaging their DNA (the molecules inside cells that carry genetic information and pass it from one generation to the next) Radiation therapy can either damage DNA directly or create charged particles (free radicals) within the cells that can in turn damage the DNA.
Cancer cells whose DNA is damaged beyond repair stop dividing or die. When the damaged cells die, they are broken down and eliminated by the body’s natural processes.
Other Methods of Radiation Therapy
Many other methods of external-beam radiation therapy are currently being tested and used in cancer treatment. These include:
Intensity-modulated radiation therapy (IMRT):
IMRT hundreds of collimators which are tiny radiation beam-shaping devices. These are used to deliver a single dose of radiation. The collimators can be stationary or can move during treatment, thus allowing the intensity of the radiation beams to change during treatment sessions. This kind of dose modulation allows different areas of a tumor or nearby tissues to receive different doses of radiation.
IMRT hundreds of collimators which are tiny radiation beam-shaping devices. These are used to deliver a single dose of radiation. The collimators can be stationary or can move during treatment, thus allowing the intensity of the radiation beams to change during treatment sessions. This kind of dose modulation allows different areas of a tumor or nearby tissues to receive different doses of radiation.
IMRT is planned in reverse, known as inverse treatment planning which is unlike other types of radiation therapy. During the process of inverse treatment planning, the radiation oncologist chooses the radiation doses to different areas of the tumour and surrounding tissue, then a high-powered computer program calculates the required number of beams and angles of the radiation treatment that is needed to treat the tumour. In contrast, during traditional (forward) treatment planning, the radiation oncologist chooses the number and angles of the radiation beams in advance and computers calculate how much dose will be delivered from each of the planned beams.
The goal of IMRT is to increase the radiation dose to the specific areas that are in need and reduce radiation exposure to specific sensitive areas of surrounding normal tissue. Compared with 3D-CRT, IMRT can reduce the risk of some side effects, such as damage to the salivary glands (which can cause dry mouth, or xerostomia), when the head and neck are treated with radiation therapy. However, with IMRT, a larger volume of normal tissue is exposed to radiation. Whether IMRT leads to improved control of tumor growth and better survival compared with 3D-CRT is not yet completely known.
Image-guided radiation therapy (IGRT):
In IGRT, repeated imaging scans (CT, MRI, or PET) are performed during treatment. These imaging scans are processed by computers to identify changes in a tumor’s size and location due to treatment and to allow the position of the patient or the planned radiation dose to be adjusted during treatment as needed. The increase in accuracy go radiation treat can be achieved by repeated imaging and may allow reductions in the planned volume of tissue to be treated, thus decreasing the total radiation dose to normal tissue.
In IGRT, repeated imaging scans (CT, MRI, or PET) are performed during treatment. These imaging scans are processed by computers to identify changes in a tumor’s size and location due to treatment and to allow the position of the patient or the planned radiation dose to be adjusted during treatment as needed. The increase in accuracy go radiation treat can be achieved by repeated imaging and may allow reductions in the planned volume of tissue to be treated, thus decreasing the total radiation dose to normal tissue.
Tomotherapy:
Tomotherapy is a type of image-guided IMRT. A tomotherapy machine is a combination of a CT imaging scanner and an external-beam radiation therapy machine. The part of the tomotherapy machine that delivers radiation for both imaging and treatment can rotate completely around the patient in the same manner as a normal CT scanner.
Tomotherapy is a type of image-guided IMRT. A tomotherapy machine is a combination of a CT imaging scanner and an external-beam radiation therapy machine. The part of the tomotherapy machine that delivers radiation for both imaging and treatment can rotate completely around the patient in the same manner as a normal CT scanner.
Very precise tumour targeting and sparing of normal tissue can be achieved as Tomotherapy machines can capture CT images of the patient’s tumour immediately before treatment sessions.
Like standard IMRT, tomotherapy may be better than 3D-CRT at sparing normal tissue from high radiation doses. However, clinical trials comparing 3D-CRT with tomotherapy have not been conducted.
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| Computed Tomography Scanner |
Stereotactic radio surgery:
Stereotactic radiosurgery (SRS) can deliver one or more high doses of radiation to a small tumour. SRS uses extremely accurate image-guided tumor targeting and patient positioning. Therefore, a high dose of radiation can be given without excess damage to normal tissue.
Stereotactic radiosurgery (SRS) can deliver one or more high doses of radiation to a small tumour. SRS uses extremely accurate image-guided tumor targeting and patient positioning. Therefore, a high dose of radiation can be given without excess damage to normal tissue.
SRS can be used to treat only small tumors with well-defined edges. It is most commonly used in the treatment of brain or spinal tumors and brain metastases from other cancer types. For the treatment of some brain metastases, patients may receive radiation therapy to the entire brain (called whole-brain radiation therapy) in addition to SRS.
SRS requires the use of a head frame or other device to immobilize the patient during treatment to ensure that the high dose of radiation is delivered accurately.
Stereotactic body radiation therapy: Stereotactic body radiation therapy (SBRT) delivers radiation therapy in fewer sessions, using smaller radiation fields and higher doses than 3D-CRT in most cases. SBRT treats tumors that lie outside the brain and spinal cord. SBRT id typically given in more than one dose as these tumours outside the brain and spinal cord are more likely to move with the normal motion of the body, and therefore cannot be targeted as accurately as tumors within the brain or spine. SBRT can be used to treat only small, isolated tumours, such as cancers in the lung and liver.
Many doctors refer to SBRT systems by their brand names, such as the CyberKnife®.
Proton therapy:
External-beam radiation therapy can be delivered by proton beams.
External-beam radiation therapy can be delivered by proton beams.
Proton beams differ from photon beams mainly in the way they deposit energy in living tissue. Photons deposit energy in small packets all along their path through tissue, whereas protons deposit much of their energy at the end of their path (called the Bragg peak) and deposit less energy along the way.
Use of protons should reduce the exposure of normal tissue to radiation, possibly allowing the delivery of higher doses of radiation to a tumour. Proton therapy has not yet been compared with standard external-beam radiation therapy in clinical trials as of yet.
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| Proton Therapy Gantry |
Other charged particle beams: Electron beams are used to irradiate surface tumours, such as skin cancer or tumours near the surface of the body, but they cannot travel very far through tissue. Thus, not being able to treat tumours deep within the body.
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.
When will a patient get radiation therapy?
Radiation therapy may be given to a patient before, during, or after surgery. Some patients may receive radiation therapy alone, without surgery or other treatments. Whereas others 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).
Does radiation therapy make a patient radioactive?
External-beam radiation does not make a patient radioactive.
However during temporary brachytherapy treatments, the patient may is radioactive when the radioactive material is inside the body 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) 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.
Bibliography
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“What to Expect When Having Radiation Therapy", <http://www.cancer.net/navigating-cancer-care/how-cancer-treated/radiation-therapy/what-expect-when-having-radiation-therapy>, 2013 (28/9/15)
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