Radiation is the process by which energy is emitted as either particles or waves. It can take the form of sound, heat, or light. Radiation therapy, also called radiotherapy, is a type of cancer treatment that uses beams of intense energy to kill cancer cells. Radiation therapy most often uses X-rays, but protons or other types of energy can also be used. The term "radiation therapy" most often refers to external beam radiation therapy, where the high-energy beams come from a machine outside of the body that aims the beams at a precise point on the body. During a different type of radiation treatment called brachytherapy, radiation is placed inside the body.
The process of radiation therapy is customized for patients, depending on which form of radiation therapy patients and their physicians choose as their options. Overall, there are five basic steps of radiation therapy: initial consultation, simulation, treatment planning, treatment delivery, and post-treatment follow-up. The initial consultation involves an appointment with a radiation oncologist, who reviews a patient’s medical records, pathology reports, and radiology images and performs a physical examination. If, based on this review, treatment by radiation therapy is chosen, the patient will be offered an appointment for simulation. During simulation, the radiation oncologist, the physicist, and dosimetrist work together to determine the precise dose and focus of radiation beams used in the treatment, based on the patients type and stage of cancer, general health, and the goals for the treatment. After the planning process, the radiation therapy team decides what type of radiation and what dose the patient will receive.
Radioactive decay is the process by which a radioactive atom becomes more stable by releasing particles and energy. Ionizing radiation is a type of radiation of such energy that it can detach electrons from atoms or molecules, which causes changes at the atomic level when interacting with matter including living organisms. Such changes usually involve the production of ions (electrically charged atoms or molecules) – hence the term “ionizing” radiation. Ionizing radiation can originate from unstable (radioactive) atoms as they are transitioning into a more stable state while releasing energy. Depending on the type of particles or waves that the nucleus releases to become stable, there are various kinds of radioactive decay leading to ionizing radiation. The most common types are alpha particles, beta particles, gamma rays, and neutrons.
