At least one in three will develop cancer. One in four men and one in five women will die from cancer.'Cancer is a disorder of cells and although is usually appearsas a tumor made up a masss of cells, the visible tumor is the end result of a whole series of changes which may of taken years to develop.'Apoptosis and cell cycle control in cancer 1996 Volume 3'.
A quantum of gamma radiation or an energetic alpha particle can pass through a small molecule in a time between 10-17 and 10-18 seconds and deliver energy to it.This will cause physical, chemical and biological changes but will only be expressed as induced cancer perhaps 30 years or more later.
There are two main techniques for delivering radiotherapy:
• An external beam of radiation is either megavoltage treatment from a linear accelerator or a linear accelerator using low energy x-rays or gamma rays from a colbalt source.The energy from the rays destroy the cancer cells on the surface or deeper in the body.This treatment is painless and is usually given for a few minutes a day in several fraction to maximise tumor killing and minimise extraneous damage to normal tissue
• Interstital (implant) irradition gives a high local dose to the tumor.Wires or needles are implanted around the tumor and radiation is given from radium, caesium or irridium. It is used in the treatment of head and neck cancers to give a high local dose without irradition to sensitive oragans such as the lens of the eye and the spinal cord.
New approaches to radiation therapy are being tested to determine their effectiveness of treating cancer. A new technique is intraoperative irradiation in which a large dose of external radiation is directed at the tumor and surrounding tissue during surgery.
Research is being carried out on a technique called radiommunotherapy this process involes the use of radiolabeled antibodies to deliver doses of radiation directly to the cancer. Antibodies are made by the highly specific proteins in response to the presence of antigens. Some tumor cells contain specific antigens that trigger the production of tumor-specific antibodies.These antibodies can be made in the laboratory and attached to radioactive substances( a process known as radiolabeling). This is then injected into the body and the antibodies seek out the cancer cells which are destroyed by the cell-killing action of the radiation. The success of this treatment is still being resaerch and will depend upon both the identification of appropiate radioactive substances and the safeness of delivering radiation in this way.