Radiation therapy
Radiation therapy is a cancer treatment that uses carefully planned doses of ionizing radiation to damage cancer cells, shrink tumors, relieve symptoms, and spare nearby healthy tissue as much as possible.
What radiation therapy is
Radiation therapy, also called radiotherapy, uses ionizing radiation as a medical treatment. It is most often used for cancer, either to cure disease, shrink a tumor, reduce the chance of recurrence, or relieve symptoms such as pain, bleeding, or pressure. The treatment is local or regional in many cases, meaning it is aimed at a defined part of the body rather than the whole body.
How it works
Radiation damages DNA and other cell structures. Cancer cells are often less able than healthy cells to repair that damage, so repeated treatment can stop them from dividing or cause them to die. Normal tissues can also be affected, which is why radiation therapy depends on careful planning, precise positioning, dose limits, and spacing treatments over time when appropriate.
External beam treatment
External beam radiation therapy uses a machine outside the body, often a linear accelerator, to aim radiation at the treatment area. Imaging and computer planning help shape the beam, choose angles, and calculate dose. Techniques such as three-dimensional conformal radiation therapy, intensity-modulated radiation therapy, image-guided radiation therapy, stereotactic treatment, electron therapy, and proton therapy are used for different situations.
Planning and simulation
Treatment planning usually begins with simulation, often using CT imaging in the position the patient will use for treatment. Masks, cushions, marks, or molds may help reproduce the same position each day. The team outlines the tumor or treatment target, nearby organs at risk, and dose goals. A plan is checked before the first treatment and monitored during the course.
Internal and systemic radiation
Not all radiation therapy comes from an external machine. Brachytherapy places a radiation source inside or near the target, such as in some prostate, cervical, breast, or skin cancers. Systemic radiation therapy uses radioactive medicines that travel through the body and concentrate in certain tissues or cancer cells. These approaches have different safety precautions and planning needs.
Side effects
Side effects depend on the body area treated, dose, schedule, other treatments, and individual health. Fatigue and skin changes are common with many external beam courses, while head and neck, chest, abdomen, pelvis, brain, or bone treatments can create different symptoms. Some effects happen during treatment; others appear months or years later, so follow-up matters.
Safety checks
Radiation therapy is built around safety checks because small errors in position, dose, target, or patient identity can matter. Teams verify the plan, machine calibration, imaging, treatment site, patient setup, shielding, and daily delivery. Medical physicists and radiation therapists play central roles in quality assurance and in making sure the prescribed dose is delivered as intended.
Why it matters
Radiation therapy matters because it can cure some cancers, improve control of others, and relieve symptoms when cure is not possible. It also shows how medicine blends biology, physics, imaging, engineering, and patient care. The central challenge is humane precision: delivering enough radiation to help while protecting normal tissue and the person's quality of life.