radiotherapy

Radiotherapy, also called radiation therapy, is a medical treatment that uses ionizing radiation to damage the DNA of cells. It aims to kill cancer cells or halt their growth, and may be delivered with curative or palliative intent. Radiotherapy can be external, placing the radiation source outside the body, or internal, via brachytherapy where radioactive sources are placed inside or near the tumor. Systemic radiotherapy uses radiopharmaceuticals that travel through the bloodstream.

Most radiotherapy is delivered as external beam radiotherapy (EBRT) using a linear accelerator that emits photons or charged particles. Modern EBRT employs advanced techniques such as intensity-modulated radiotherapy, image-guided radiotherapy, image guidance, and motion management to concentrate dose in the tumor while sparing surrounding normal tissue. Brachytherapy delivers high doses in a short time by placing sources directly into the tumor or adjacent tissue. Proton therapy and other particle therapies use charged particles with distinct dose distributions.

Planning relies on imaging (CT, MRI, PET) to define the tumor and organs at risk. The total dose is divided into daily fractions over weeks; typical curative regimens deliver 1.8–2 Gy per day, with total doses around 45–70 Gy, whereas SBRT involves fewer, higher-dose fractions.

Common side effects reflect the treated area and may include fatigue, skin changes, or mucosal irritation; most are temporary, with some late effects possible. Radiation therapy is a cornerstone of cancer treatment and is often combined with surgery, chemotherapy, or immunotherapy.