Radiotherapy Health Article

Definition

Radiotherapy is the use of high-energy penetrating radiation (x rays, gamma rays, proton rays, and neutron rays) to kill cancer cells.

Purpose

The primary purpose of radiotherapy is to eliminate or shrink localized cancers. It is also sometimes used to treat metastases—often brain metastases—in cases in which surgical treatment would be riskier. The aim of radiotherapy is to kill as many cancer cells as possible, while doing as little damage as possible to healthy tissue. In some cases, the purpose is to kill all cancer cells and effect a cure. In other cases, when cures are not possible, the purpose is to alleviate the patient's pain by reducing the size of the tumors that cause pain.

For some kinds of cancers (for example, Hodgkin's disease, non-Hodgkin's lymphoma, prostate cancer, and laryngeal cancer), radiotherapy alone is often the preferred treatment. Radiation is, however, also used in conjunction with surgery, chemotherapy, or both; and survival rates for combination therapy in these cases are often greater than survival rates for any single treatment modality used alone. Radiotherapy is especially useful when surgical procedures cannot remove an entire tumor without damaging the function of surrounding organs. In these cases, surgeons remove as much tumor mass as possible, and the remainder is treated with radiation (irradiated).

Precautions

Radiotherapy has serious side effects; therefore, anyone considering it should be sure that it is the best possible treatment option for their cancer. Cancer treatment research moves so rapidly that some doctors may not be aware of the latest advances in treatments outside their own specialties that might be safer and better. Accordingly, patients who have had radiotherapy recommended to them should consider getting a second opinion.

Description

Radiotherapy is also known as radiation therapy, radiation treatment, x-ray therapy, cobalt therapy, and electron beam or "gamma knife" therapy. Recent advances in medical technology have made it even more useful for patients and have reduced some of its unpleasant side effects. Radioactive implants allow delivery of radiation to localized areas, with less injury to surrounding tissues than radiation from an external source that must pass through those tissues. Proton radiation also causes less injury to surrounding tissues than traditional photon radiation, because proton rays can be tightly focused. Current research with radioimmunotherapy and neutron capture therapy may provide ways to direct radiation exclusively to cancer cells—and in the case of radioimmunotherapy, to cancer cells that have metastasized (spread to other sites throughout the body).

How radiotherapy works

High-energy radiation kills cells by damaging their DNA and thus blocking their ability to divide and proliferate. Other cytotoxic mechanisms include the production of poisonous OH^- free radicals in the cellular cytoplasm.

Radiation kills normal cells about as well as cancer cells; but cells that are undergoing rapid growth and division (such as cancer cells, skin cells, blood cells, immune system cells, and digestive system cells) are the most susceptible to radiation. Fortunately, most normal cells are better able to repair radiation damage than are cancer cells. Accordingly, radiation treatments are parceled into component treatments that are spaced over a given time interval (usually about seven weeks). The spacing of radiation treatments allows cells to repair themselves during the time between treatments. Since the repair rate of normal cells is greater than the repair rate of cancerous cells, a smaller fraction of the radiationdamaged cancerous cells will have been replaced by the time of the next treatment. This procedure is called fractionation because the total radiation dose is divided into fractions. Fractionation allows cancer cells to be killed more effectively with less ultimate damage to the surrounding normal cells. Ideally all the cancer cells will be gone after the last treatment session.