Radiation Therapy

Radiation Therapy



Roberta Anne Strohl



DEFINITION


Radiation therapy is a local treatment for cancer. It is the use of high-energy particles or x-rays, which possess sufficient energy to create ionizing radiation by ejecting electrons from their orbit. The effects of radiation occur because of physical, chemical, and biochemical factors. Physical factors consist of the energy of the radiation that is able to eject electrons, creating instability. Chemical reactions occur because ionization creates powerful oxidizing and reducing agents, known as free radicals, in cellular fluid. The target of radiation effect is cellular deoxyribonucleic acid (DNA). Radiation results in biochemical damage of the chemical bonds, which loosely hold DNA together. Double-strand breaks in DNA are the most important effect of radiation on cells.



RADIOBIOLOGY


Apoptotic, or programmed, cell death is enhanced by radiation. Radiation damage most often occurs at the time the cell attempts to divide. Cells are most sensitive to radiation damage during the G2 and M phases of the cell cycle and least sensitive during S phase. Cells that have a higher mitotic index are more sensitive to radiation damage.


Normal cells have a better ability to recover and repair from radiation damage than do cancer cells. Despite this ability, there is a maximally tolerated radiation dose for normal cells, and treatment above that dose may result in irreparable damage. The delivery of radiation must balance the dose of radiation needed to treat the given tumor cell line and the dose that is tolerated by the surrounding normal tissues. When there is a wide margin between the dose that must be given and the tolerance of the surrounding tissue, the treatment course may be short and will be better tolerated than when that margin is narrow. For example, cancers in the head and neck area require a high radiation dose, which is difficult for the mitotically active oral mucosa to tolerate.



RADIATION DELIVERY



External Beam Therapy


This is the most common delivery system for radiation. The linear accelerator is a treatment machine, which generates ionizing radiation by accelerating electrons along a tube. In this form of radiation, the patient is positioned on a treatment couch and through a sophisticated system of planning; the radiation beam is directed to the tumor site. The total dose of radiation required is achieved through equal daily fractions of radiation, usually given one a day, 5 days per week, until the total dose is reached. Patients receiving this form of radiation are not radioactive.



Brachytherapy


Radioactive material is placed into the tumor or near the tumor site. This is implant treatment. The implant may be temporary or permanent. Temporary implants are more common and are used in clinical situations where a local radiation dose required is higher than can be achieved with external beam therapy because it would exceed the normal tissue tolerance. Implants deposit most of the radiation dose in a small-volume area. The radioactive sources are sealed in metal carriers. Patients having implants are radioactive for the period of time that the source is in them. Because the radiation source is sealed, there is no contamination of the body fluids. Nurses caring for these individuals are instructed to observe the precautions of time, distance, and shielding to protect themselves from radiation exposure. This means spending a defined amount of time at a defined distance from the source and to use shielding as available.


Permanent implants are the insertion of radioactive materials that are not removed. The sources used are weak emitters of gamma radiation yielding low surface doses. Iodine 125 used in prostate cancer is the most common permanent implant in cancer care.

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Mar 1, 2017 | Posted by in NURSING | Comments Off on Radiation Therapy

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