Radiation Therapy: A Treatment Option for Cancer

Radiation therapy is the use of penetrating beams of high-energy X-rays, electron beams or radioactive isotopes to destroy the cancerous cells by interfering with its reproduction.  A cell is the basic unit of all organs, muscles and tissues in the human body. At the center of the cell is the nucleus that contains chromosomes in which are embedded arrays of genes. The chromosomes control all the functions of a cell. New cells originate from the existing cells by the process of cell division. Uncontrolled multiplication of cells leads to malignancy or cancer.

There are many ways of treatment of cancer, including surgery, chemical therapy and radiation therapy. Chemotherapy involves the use of drugs and is a systemic treatment, whereas radiation therapy is a localized treatment. This means it affects only the cells in the specific areas of the body where the radiation is directed. Radiation therapy is sometimes used in combination with other therapies.
 
When the rays or particles from the radiation unit enter the cell’s nucleus, they interact with water present in the nucleus, and form a free radical called hydroxyl radical. The hydroxyl radical is unstable and causes damage to the cell’s DNA. The radiation affects those cells that are undergoing a rapid division, which is indeed the case with cancerous cells. Due to this damage, some cells die immediately. Even the cells that survive are unable to divide and will die at the time of cell division.

Normal, healthy cells are affected by radiation therapy as well, and this accounts for the adverse side effects seen with this type of treatment. But unlike malignant cells,  they are able to repair the effects of radiation in a few months. To help minimize their damage, radiation is divided into doses or fractionated and spread out over time.

The present day technology allows deeper penetration of the radiation with minimal scatter to healthy tissues. To target the malignant cells as closely as possible, the radiation therapist uses CT scan, an MRI, or a barium enema, to determine the exact area that needs treatment. A CT scan is a type of x-ray that uses a computer to produce cross-sectional images of the inside of the body. An MRI scan uses magnetic waves to produce two and three dimensional images of the inside of the body. A barium enema helps to create better x-ray images through radioactive coating the lining of the colon and rectum by a rectal injection of barium. With this information as the basis, the maximum radiation to be directed at the tumor is calculated, while minimizing the dose to the normal surrounding tissues.

Radiation therapy can be given before surgery to shrink a cancerous tumor. It can also be used after surgery to stop the growth of any remaining cancer cells.
  
Radiation can come from a variety of energy sources, including X-rays and gamma rays, and particle beams such as electrons, protons and neutrons from radioisotopes. Cobalt-60 and  Cesium-137 are the main isotopes used for treatment. Radiation from each of these vary in the type of energy emitted, the amount of area it can cover and the degree of penetration.

Apart from external radiation as described above, internal radiation (brachytherapy) is also used, wherein the radiation source is kept within the cancerous node or very near to its surface. Normally natural cavities of the human body are used for placing the radiation source inside the body. Cesium-137, Cobalt-60 and Iridium-192 are used for this type of treatment.