Radiation therapy (sometimes called radiotherapy, x-ray therapy, or irradiation) uses high energy x-rays to kill 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. Radiation therapy can damage normal cells as well as cancer cells. Therefore, treatment must be carefully planned to minimize side effects.
The radiation used for cancer treatment may come from a machine outside the body (external beam radiotherapy), or it may come from radioactive material placed in the body near cancer cells (internal radiotherapy, brachytherapy) One type of radiation therapy commonly used involves photons, "packets" of energy. The higher the energy of the x-ray beam, the deeper the x-rays can go into the body. Linear accelerators are machines that produce high energy x-rays.
Radiation therapy may be used alone or in combination with chemotherapy or surgery. The total dose of radiation and the number of treatments will depend on the size and location of the cancer, your general health and other medical treatments you may be receiving. Radiation therapy is typically given five days a week for 4 to 6 weeks. When radiation is used for palliative care, the course of treatment is shorter, usually 1 to 2 weeks.
Stereotactic radiosurgery (SRS) can deliver one or more high doses of radiation to a small area of cancer. SRS uses extremely accurate image-guided 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 cancers with well-defined edges. It is most commonly used in the treatment of cancer in the brain as well as in liver or lungs. 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.
Volumetric Modulated Arc Therapy
Volumetric Modulated Arc Therapy (VMAT) is a new radiotherapy method first performed in the Sydney at Mater Hospital, North Sydney. Using three-dimensional volume imaging, treatment can be designed and delivered to maximise the radiation dose the tumour receives and minimise exposure of the surrounding healthy tissue. The angle of the beam, the dose rate and the leaf speed are all independently controlled, making this a very accurate form of treatment. Arc therapy treatments also take much less time to deliver than other radiotherapy techniques.
Brachytherapy is different to the other treatments listed above. Instead of the ionising radiation source being outside the body, patients have radioactive sources placed inside their body. This can be done in an operating theatre under anaesthetics and patients may require to stay in hospital for a few days.
Prior to the start of radiation therapy, you will have to go through a process called simulation (planning). During simulation, you will be asked to lie very still on an examining table while the radiation therapist uses a special CT scan machine to image your treatment field. Simulation may also involve CT scans or other imaging studies to accurately plan how to direct the radiation.
Depending on the type of treatment you will be receiving, face masks, body moulds or other devices that keep you from moving during treatment (immobilization devices) may be made at this time. They will be used each time you have treatment to ensure you are positioned correctly. The radiation therapist will often mark on your skin with tattoos or tiny dots of coloured, permanent ink. These tattoo marks are used to set up treatment field each day. Simulation may take from half an hour to approximately one hour. Once completed, your doctor will meet with the radiation therapist to design an individual treatment plan for you and this may take 3-4 days.
Before each treatment, you may need to change into a hospital gown. It's best to wear clothing that is easy to take off and put on again. In the treatment room, the radiation therapist will use the tattoo mark on your skin to locate the treatment area and to position you correctly. For each external radiation therapy session, you will be in the treatment room about 10 to 20 minutes, but you will be getting radiation for only about 2 to 5 minutes of that time.
Receiving external radiation treatments is painless, just like having an x-ray taken. You will not hear, see, or smell the radiation.
The radiation therapist may put special shields (or blocks) between the machine and certain parts of your body to help protect normal tissues and organs. You need to remain very still during the treatment so that the radiation reaches only the area where it is needed and the same area is treated each time. You don't have to hold your breath — just breathe normally.
The radiation therapist will leave the treatment room before your treatment begins, to operate the equipment. Although you may feel alone, keep in mind that the therapist can see and hear you and even talk with you using an intercom in the treatment room (you will be watched on a television screen in the control room). If you feel ill or very uncomfortable during the treatment, tell your therapist at once. The machine can be stopped at any time.
After starting treatment, your doctor and members of your health care team will follow your progress at least once a week, by checking your response to treatment and how you are feeling. When necessary, your doctor may revise the treatment plan by changing the radiation dose or the number and length of your remaining radiation sessions.
Like all forms of cancer treatment, radiation therapy can have side effects. Possible side effects of radiation include temporary or permanent loss of hair in the area being treated, skin irritation, temporary change in skin colour in the treated area, and tiredness. Other side effects are largely dependent on the area of the body that is treated. More information about the side effects associated with radiotherapy can be obtained from your radiation oncologist.
External radiation therapy does not cause your body to become radioactive. There is no need to avoid being with other people because you are undergoing treatment. Even hugging, kissing or having sexual relations poses no risk of radiation exposure.