Radiation therapy or radiotherapy, also called radiation oncology, is the use of ionizing radiation as part of cancer
treatment to destroy malignant cells.
Cells reproducing at abnormally high rates are known as Tumors . Radiation therapy specifically acts against such cells that are reproducing rapidly. Normal cells stop reproducing or dividing as they come into contact with other cells. But in the case of a tumor, dividing of the cells does not stop and the cells continue to divide over and over. It is due to the DNA of the cell that makes it capable of reproducing.
In Radiation therapy high energy x-rays are used to damage the DNA of cells, thus it kills the cancer cells, or else stop them from reproducing.This damage is caused by a photon, electron, proton, neutron, or ion beam directly or indirectly ionizing the atoms by which DNA chain is made up of. Indirect ionization occurs due to the ionization of water, forming free radicals, notably hydroxyl radicals, which damages the DNA. Most of the radiation effect is through free radicals, is commonly used form of radiation therapy. But cells have the mechanisms to overcome the DNA damage. So this technique proves to be the most effective in modifying cell characteristics by breaking the DNA on both strands .Because cancer cells are generally undifferentiated and stem cell-like, they reproduce fast and have the capability to repair sub- lethal damage as compared to most healthy differentiated cells. But this damage in DNA is accumulating to the cancer cell which it inherits through cell division,as a result causing them to die or reproduce more slowly. But normal cells are also damaged through Radiation. Actually normal cells grows slowly, so they are capable of repairing this radiation damage better then the cancer cells.
Types of Radiation Therapy:
There are mainlytwo main types of radiation therapy : -
a). External radiation therapy In this case a beam of radiation is directed from outside the body. In internal radiation therapy which is also known as brachytherapy or implant therapy, here a radioactivity source is placed surgically inside the body near the tumor.
b). External radiationThis is also known as x-ray therapy, cobalt therapy, proton therapy, or intensity modulated radiation therapy (IMRT). In this type of radiation a machine called a linear accelerator is used to administered .Depending on the treatment protocol being used, once or twice a day this treatment can be given.
Five days a week and for several weeks the treatments goes on, which depends on the total final dose of radiation that has been planned. In order to give normal cells some time to heal, on weekends patients are given a break from treatment , which reduces the side effects. Someone receiving external radiation therapy is neither radioactive nor dangerous to the people surrounding him or her.
In Internal radiation therapy the source of high-energy rays is placed inside the body, mostly close to the cancer cells. This is done by implanting small pieces of the radioactive substance or else by implanting a reservoir, in which a liquid radioactive substance is injected. Very intense radiation is delivers through this to a small area of the body which limits the dose to the normal tissue. When compared with external treatment internal radiation therapy allows the doctor to give a higher total dose of radiation in a shorter time .
According to experts in there theory of RADIATION THERAPY IN THE MANAGEMENT OF CANCER has stated that "Radiation oncology is relatively a new subject as compared to other medical specialties. However, there is no other medical field which had more speedy evolution than radiation oncology. Within a short span, it has attained tremendous growth and made a place for itself in the medical science showing its utility in the welfare of mankind. This has resulted in accurate target localization and precise delivery of radiation to the target area resulting into better tumor control, minimal normal tissue complications and to some extent improved survival rates.
According to him understanding the basic principles of radiotherapy is essential to the successful use of radiation therapy.
These include: The higher the dose of the radiation delivered to the tumor, higher the probability of the local control of the tumor. Hence, generally the aim is to deliver the maximum dose to the tumor without causing undue toxicity to the surrounding normal tissues. The lower the dose to the surrounding normal tissues, the lower the associated morbidity, hence the radiation oncologists use multiple beams, optimized treatment planning, shielding, brachytherapy and other techniques to limit the dose to the surrounding normal tissues, thereby minimizing the morbidity. Larger tumors require higher doses of radiation for control. Conversely, small or microscopic tumors require lower doses for control.
Tumor cells usually proliferate faster than the normal tissues. Shortening the time interval between surgery and radiation therapy reduces the repopulation of tumor cells. Hence prolonged delays between surgery and start of radiation therapy should be avoided.
There are basically two types of radiation treatment:
1) External Beam Radiation Therapy (EBRT)
A patient may receive one or the other, or a combination of both External Beam Radiation Therapy (EBRT) or teletherapy denotes treatment of patient when the source of radiation lies outside the body.
Brachytherapy is the treatment with radioactive material implanted into the tumor bearing area. The various radioactive materials used are Iridium-192, Caesium-137, Iodine-125 and Palladium-103 etc. Currently the brachytherapy treatment is performed with the help of Remote After loading Units where there is no risk of radiation exposure to the staff personnel. Brachytherapy has the advantage of delivering high dose of radiation in shorter time simultaneously sparing the surrounding normal structures. The usual treatment with low dose rate (LDR) brachytherapy takes about 3 days and requires one or more fractions. On the other hand HDR brachytherapy treatment is delivered in minutes but multiple fractions (average 3-7 fractions) are required. The tumors where brachytherapy is preferred are cancers of cervix cancer, endometrium, esophagus, head & neck and chest wall tumors.
Steps in radiation treatment:
Consultation: At the beginning, the patient is examined by the radiation oncologist for a consultation. During the consultation, the radiation oncologist takes a history and performs a physical examination. He reviews all the pertinent data and all of the investigations that have been performed. He may also request other tests or consultations to be made.
Simulation: The next step is simulation or treatment planning. After the consultation, the radiation oncologist formulates a treatment plan. Here, the patient comes to the radiation department and lies down on a table under a machine, called a simulator. Various immobilization devices may be necessary, such as a head rest or a face mask, in order to make sure the patient is positioned correctly and in the same way for each treatment. There will be various markings that will be made on the skin and various x-rays are taken. The patients may require more than one session for simulation. Simulation is very important, since it is the step that allows for proper planning and delivery of the actual treatment. After simulation, there is a lot of behind-the-scenes work. Here the medical physicist is involved. CT scans may have to be taken in order that the computers can calculate and prescribe the dose distribution of the radiation.
Blocks and shields are often fashioned for the patient undergoing radiation treatment. Blocks or shields are pieces of lead that are placed on a tray between the patient and the treatment machine. The blocks basically will cover up normal tissues in the body in order that radiation is delivered principally to the tumor. External radiation is a safe and basically painless form of treatment.
The treatment is painless. Patients do not hear or feel anything during or after the treatment. Patients then return on schedule to complete the treatment course. During the radiation course, patients are monitored by the radiation oncologist and his/her staff. These are called status checks. Patients should inform the radiation oncologist of any new symptoms. The side effects/accompaniments of the radiation depend on the exact type of tumor treated and the location of the radiation treatment. During the course of treatment, patients undergo blood tests, sometimes once a week. Radiation works best when it is given in small doses over several sessions. In this way, it can kill the tumor cells and yet allow sufficient time for the normal healthy cells around the tumor to repair any damage from the radiation.
Healthy cells along with the cancer cells is also get damaged through Radiation therapy. This damage causes side effects. Mostly healthy cells of the body recover shortly after the therapy is stopped. These side effects depends on what body parts are treated, and on the radiation dose.
Side effects include :-
2.Hair loss on the treated body part
3.Skin irritation like a bad sunburn on the treated body part
4.Nausea, vomiting or diarrhea, if the abdomen is treated
5.Mouth sores, a sore throat or dry mouth, if the head or neck is treated
These side effects generally go away within a few weeks when the treatment is over.
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