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Radiation Therapy for Cancer

Radiation therapy is known by several names including radiotherapy and x-ray therapy. This type of cancer treatment directs a carefully controlled amount of radiation at a specific area of the body.

How does radiation therapy work?

Radiation is commonly used in the diagnostic x-rays, CT scans and dental x-rays. However, radiation therapy uses much higher x-ray energy to deliver a many times stronger dose to treat cancer. These high doses can wipe out abnormal cells by destroying the genetic material that controls the growth of these cells. Some healthy cells will also be destroyed but the goal of this treatment is to kill off as many of the cancerous cells while minimizing its impact on the healthy cells. Cancer cells are more susceptible to radiation therapy because they divide more rapidly than healthy cells and are vulnerable to damage while dividing. It helps in this fight against cancer that healthy cells can recover from the treatment faster and more effectively than the cancer cells can.

How is radiation therapy delivered?

Radiation therapy is used in two ways; externally and internally.

Externally – is the most common form of radiation therapy. This technique uses a large machine, a linear accelerator, to deliver high doses of radiation to the specific location. This machine delivers the radiation in a continuous stream of fast-moving subatomic particles. Generally, this treatment is done on a daily basis for around four - six weeks, depending on the individual case.

Internally - this treatment process is also known as brachytherapy, meaning short distance therapy, and includes both interstitial and intracavitary radiation. This treatment uses special radioactive substances about the size of grain of rice, called seeds or pellets.

  • Interstitial radiation is when the radiation source is placed directly in or next to the tumor using pellets, wires, tubes or containers.
  • Intracavitary radiation is when a container of radioactive material is placed in a specific body cavity, such as the vagina.
  • In order to place these radioactive sources in the right place, the physicians use x-rays, ultrasound or CT scans. These implants, depending on the treatment plan, can be either permanent or temporary.
  • Permanent – involves low dose radiation placing these pellets or seeds directly into tumors using very fine hollow needles. Once in place, the pellets give off radiation for several weeks or months. Due to their tiny size, these implants are left in place even after their radioactive material is used up.
  • Temporary – involves high dose radiation where hollow needles, tubes, or balloons filled with fluid are placed into the area to be treated. These are left in for a short period of time and then removed. This process will be repeated over several days to weeks. Lying calm and still during treatment is required to stop the implant from shifting.
  • Radiopharmaceuticals - These are drugs that contain radioactive materials. These drugs can be given through an IV line, orally, or into a body cavity. Depending again on the drug and how it is given to the patient, these radioactive materials travel to various parts of the body. This method is used extensively for some conditions, such as bone pain and thyroid cancer. Examples of these drugs are:
    Phosphorus 32 – infused through a catheter in the space in the abdomen or between the linings around the lungs. It can also be injected directly into certain tumors.
  • Strontium 890 and samarium 153 – both used for tumors that have spread to the bone. Can be given through an IV and will travel to areas of the bone where there is cancer
  • Iodine 131 – destroys cancer cells in the thyroid gland with limited damage to the rest of the body.

How is radiation therapy used in cancer treatments?

Multimodality therapy for mesothelioma

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