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About Radiation

Radiation involves using high-energy radiation beams in a very focused way to treat or cure cancer, or to provide relief from cancer symptoms. Approximately half of all cancer patients require radiation treatment at some point during the course of their illness.

Radiation treatment is the use of a certain type of energy (radiation) from X-rays, gamma rays and electrons to destroy cancer cells. In high doses, radiation destroys cells in the area being treated. It does this by damaging the DNA (genetic information) in cancer cell genes, making it impossible for them to grow and divide. During radiation treatment, both cancer cells – which are growing in an uncontrolled way – and healthy cells are affected, but most healthy cells can repair themselves.

In some cases, patients may receive radiation treatment alone, without surgery or other treatments. Some patients may receive radiation treatment and chemotherapy at the same time (often called “chemoradiation”). For some types of cancer, the combination of chemotherapy and radiation may destroy more cancer cells (increasing the likelihood of a cure), but it may also cause more side effects.

Radiation Timing

Patients may receive radiation therapy before, during or after surgery. The timing of radiation treatment depends on the type of cancer being treated and the goal of treatment (cure or to lessen symptoms):

  • 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.
  • Radiation given after surgery is called post-operative or adjuvant radiation treatment.

There are 2 main types of radiation treatments: external beam radiation therapy and brachytherapy. The type and stage of cancer you have, along with factors such as other medical conditions and previous medical procedures, will determine which type of radiation you receive.

External Beam Radiation Therapy

In external beam radiation therapy, radiation is directed at the cancer and surrounding tissue from a machine outside the body. This type of treatment is used to treat most cancers and is most often delivered in the form of photon beams (either X-rays or gamma rays).

Common types of external beam radiation treatment include:

  • Intensity-modulated radiation therapy (IMRT) – IMRT uses sophisticated computer software and advanced treatment machines to deliver radiation to precise areas. Hundreds of very small radiation beam-shaping devices (collimators) allow the intensity of the radiation beams to change during treatment sessions, as specified by patients’ unique treatment plans. The goal of IMRT is to increase the radiation dose to areas that need it (for example, a tumour) and reduce radiation exposure to the surrounding normal tissue.
  • Volumetric arc therapy (VMAT) – VMAT is an advanced form of IMRT, which delivers treatment to a precise area. During regular IMRT treatments, the radiation treatment machine must rotate several times around the patient or make multiple stops/starts to deliver treatment to the tumour from a number of angles. Using VMAT, treatment can be delivered to the tumour in a 360-degree rotation more quickly.
  • Image guided radiation therapy (IGRT) – In IGRT, repeated imaging (CT, MRI) is performed during treatment to spot changes in a tumour’s size and location (which change due to treatment) and allow adjustments to be made to the patient’s position or the planned radiation treatment dose. These adjustments are important to make sure that the appropriate area is treated every day.
  • Stereotactic body radiation therapy (SBRT) – SBRT delivers radiation in fewer sessions, using high doses and to small areas. SBRT is typically used to treat small, isolated tumours, including cancers in the lung and liver.
  • Stereotactic radiosurgery (SRS) – Used to treat small tumours, SRS delivers 1 or more high doses of radiation. SRS is most commonly used to treat brain or spinal tumours as well as brain metastases.

  • Proton therapy – This form of external beam radiation treatment uses proton beams instead of the photon beams mentioned earlier. Proton therapy is being investigated for use in the treatment of other cancers, however, at this time it is most commonly used for the treatment of pediatric brain tumours.


In brachytherapy, sealed radioactive sources are placed inside the body, in or near the cancer. A sealed radioactive source is often called an implant. Brachytherapy makes it possible to treat the cancer with a high total dose of radiation in a concentrated area in a short period of time.

To destroy cancer cells properly, it’s very important for the radiation to target the exact area where the cancer is and that your exposure is continually watched. There are several steps in the radiation treatment process to make sure your treatment is as successful as possible:

  • Simulation – This is the first step in creating your personalized treatment plan. A simulator (a special scanner) takes pictures (3D imaging) of your treatment area. These pictures are then used to design your treatments.
  • Planning – After your simulation appointment, your radiation team uses the information to design your treatment plan. They decide how many radiation treatments you need and how much radiation you will receive at each appointment.
  • Treatment – The first session usually lasts about 30 minutes, while the other treatment sessions are around 15 to 20 minutes each. You will lie on a treatment bed in the position determined during the planning phase. The bed will be moved under the linear accelerator (the radiation machine), which delivers the radiation. If the goal is to cure the cancer (curative), radiation treatment is usually given daily for 3 to 8 weeks. If the goal is to lessen symptoms (palliation), the treatment is often given over a shorter timeframe.
  • Review – This weekly appointment with your radiation oncologist and oncology nurse reviews how your treatment is going and helps with any side effect concerns.

  • Follow-up – In the last week of your treatment you will receive a follow-up appointment to come back for a meeting with your radiation oncologist, usually 4 to 8 weeks after you finish treatment.