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Radiotherapy Physics

Article Index

What is cancer?

Normally the cells that make up the body grow, divide, and replace themselves in an orderly manner. Sometimes, however, this order is upset and the cells divide abnormally to form cancerous cells.

Tumours can be either benign or malignant. Benign tumours are not cancer. They usually grow slowly, and generally do not spread to other parts of the body. Benign tumours can usually be removed surgically without any further problems. Malignant tumours are cancer. They are usually capable of invading adjacent tissues or metastasising (spreading) to other parts of the body. The most common methods for cancer to spread are through the lymphatic system to regional lymph nodes or through the bloodstream to distant organs.


How is cancer treated?

There are three major methods of treating cancer--surgery, radiation therapy, and chemotherapy.

Surgery involves the removal of the tumour and some of the surrounding normal tissues. This is a very localised form of treatment.

Radiation therapy involves the use of ionising radiation to destroy cancer cells. Radiation therapy is also a localised form of treatment. However, it is broader in scope than surgery because organs that cannot be removed surgically can usually be treated with irradiation.

Chemotherapy uses anticancer medication to destroy cancer cells. The drugs may be given by mouth, intramuscularly, or intravenously. Because the chemotherapy agents travel throughout the body, it can eradicate cancer cells in remote locations but at the same time cause damage to the body as a whole.

Many cancers are treated with a combination of these treatment modalities.


What is radiation therapy?

Radiation therapy is the careful use of high energy x-rays, gamma rays, or electrons to treat cancer. Radiation is effective in treating cancer because it damages cancer cells more than it does normal cells. However, normal tissues may also be damaged, which is one reason why side effects can occur. The goal of radiation therapy is to destroy the cancer with as little injury as possible to the surrounding normal tissues.

The purpose of radiation therapy is often to cure the patient of cancer. Such treatment is called curative radiotherapy. To be curative, the treatment must eradicate every cancer cell or prevent them from growing and multiplying. High doses are often required when the aim of the radiation therapy treatment is to cure. Radiation therapy may also be used to relieve cancer symptoms, even when cure is not possible. This type of treatment is called palliative radiotherapy.


How is radiation therapy given?

There are two main types of radiation therapy- external beam radiation therapy and radioactive implants. With external beam radiation therapy, a machine is used to direct the radiation to the cancer through the skin. Most of the patients who are treated with radiation therapy are treated with external beam irradiation.

With radioactive implants, radioactive sources are placed inside the body within or next to the tumour. Radioactive implants are often used to treat well-localised cancers because a greater dose of radiation can be given to the tumour with less dose to surrounding healthy tissues. It is not unusual for a patient to receive a combination of external beam radiation therapy followed by a radioactive implant.


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