Radiation therapy is the process in which a patient that has cancerous tumors undergoes radiation therapies in an attempt to remove the growth from the body. Radiation therapy targets very specific locations on the body so that healthy tissues remain healthy and unaffected by the radiation. Some forms of cancer are not remote and require systemic radiation treatments in which the patient either imbibes or is injected by a radiated substance in order to kill the cancerous cells. The high-energy radiation shrinks malignant or benign tumors in hopes of destroying all cancerous cells. Not all cancer patients receive radiation therapy; in fact, about half of cancer patients are treated with radiation. Radiation therapy is the most effective way to kill cancerous cells if the cancer cannot be removed via surgery. Radiation therapy has saved the lives of countless people and is a true marvel of our modern technological advances.
Radiation therapy damages the DNA of harmful cancer cells by blasting the cancer cells with high-powered radiation. The high-energy radiation does not just affect the cancer cells though, it affects all cells near where the radiation is targeted. To ensure that the radiation is not killing healthy cells, the radiation has to be carefully targeted and planned out. The radiation therapy is specially used to shrink tumors and kill all cancer cells. When the DNA cells of the cancer are destroyed enough, they will stop dividing and die. The body takes the dead or unproductive cells and eliminates them through natural bodily processes. Even though radiation therapy is meant to kill body cells, it is meant for good. Because cancer cells are surrounded by normal healthy cells, nothing can prevent the good cells to be killed as well since they are so close to the area being bombarded by the radiation. 
There are three basic types of radiation therapy: external-beam radiation therapy, internal radiation therapy, and systemic radiation therapy. The radiation treatment a patient receives is dependent upon: the type of cancer, the size of the cancer,the cancer’s location in the body, how close the cancer is to normal tissues that are sensitive to radiation, how far into the body the radiation needs to travel, the patient’s general health and medical history, whether the patient will have other types of cancer treatment,the patient’s age, and other medical conditions. There are various kinds of external-beam therapies. The methods used for external-beam therapy are as follows: Intensity-modulated radiation therapy (IMRT, Image-guided radiation therapy (IGRT), Tomotherapy, Stereotactic radiosurgery, Stereotactic body radiation therapy, Proton therapy, and Other charged particle beams. External-beam therapy is groups of photon beams as either x-rays or gamma rays that usually target very precise areas to kill cancerous cells. Internal radiation therapy is radiation that is put into the body, either directly into the tumor tissue, or into a surgical or bodily cavity near the tumor. In systemic radiation therapy, the patient either swallows or receives an injection of a radioactive material.
Radiation therapy dates all the way back to 1896 where a doctor named Wilhelm Conrad Roentgen from Germany gave a lecture on the possibilities of X-ray technologies. Within three years, X-rays were being used to kill cancer cells and ultimately treat cancer. Discovering and greatly improving radiation therapies over the years has not gone perfectly though. Many tests trying to determine correct doses and risks of radiation have gone wrong. In some of the earlier years of using radiation as a cure for cancer, doctors would test the strength of the radiation by exposing their arm to it until it turned a pink color that resembled a sunburn. This was called the erythema dose. Many of these earlier radiologists ended up getting leukemia themselves because of all the radiation they exposed themselves to. Now, radiation machines are very advanced. The radiation beams are matched to the size and shape of the tumor, and the pin-point radiation beams are aimed from several directions onto the tumor. 
There can be numerous side effects to receiving radiation therapy that can last for months or years. The side effects that a patient has is dependent upon what part of the body someone receives the radiation treatment on, the daily dose, the overall dose, and the person's medical health. Acute side effects that appear when areas of rapidly dividing normal cell production is damaged often cause skin irritation, hair loss, urinary problems, and damage to salivary glands. Fatigue is a constant side effect that affects all patients regardless of where the cancer treatment is on the body. Nausea is prevalent in patients that undergo radiation treatments in the abdomen or the head. Other common side affects that show up in radiation cancer treatment patients are: fibrosis, damage to the bowels which cause diarrhea and/or bleeding, memory loss, infertility, or even a second cancerous tumor could appear (though very rare).