Radiation

Radiation therapy is one of the central conventional treatments for cancer. It uses ionizing radiation, most commonly high-energy photons, electrons, protons, or implanted radioactive sources, to damage DNA and other critical cell structures. Cancer cells often have impaired repair capacity and rapid growth signals, making a carefully delivered radiation dose able to stop division, trigger cell death, shrink tumors, or sterilize microscopic disease left behind after surgery.

How It Is Used

Radiation may be used as the main curative treatment, before surgery to shrink a tumor, after surgery to lower recurrence risk, with chemotherapy as chemoradiation, with systemic therapy for organ preservation, or as palliative treatment for pain, bleeding, airway obstruction, brain metastases, spinal cord compression, or bone metastases. Treatment intent, dose, and schedule vary by cancer type, stage, tumor location, prior radiation exposure, and nearby organs at risk.

Major Forms

External beam radiation therapy uses a machine outside the body to aim radiation at the tumor. Modern forms include three-dimensional conformal radiation therapy, intensity-modulated radiation therapy, image-guided radiation therapy, volumetric modulated arc therapy, stereotactic radiosurgery, stereotactic body radiation therapy, electron therapy, and proton therapy. Internal radiation, or brachytherapy, places radioactive seeds, ribbons, capsules, or applicators in or near the tumor. Systemic radiopharmaceutical therapy uses radioactive medicines that travel through the body to target certain cancers or metastases.

Effectiveness and Limits

Radiation is highly effective for many localized and regional cancers and is a major part of breast, prostate, head and neck, lung, cervical, rectal, brain, skin, lymphoma, pediatric, sarcoma, and palliative oncology care. Its strength is local control. Its limits include normal-tissue tolerance, tumor motion, tumor radioresistance, prior radiation dose, and the fact that local radiation alone cannot treat widespread microscopic disease throughout the body.

Side Effects and Safety

Radiation side effects depend on the body area treated, total dose, fractionation, treatment volume, and concurrent therapy. Common issues include fatigue and site-specific effects such as skin reaction, mouth or throat irritation, swallowing difficulty, nausea, bowel or bladder symptoms, fertility effects, hair loss in the treated field, fibrosis, lymphedema, dry mouth, or late organ injury. Modern planning attempts to maximize tumor dose while limiting normal-tissue exposure. Most external beam radiation does not make the patient radioactive, while some internal or systemic treatments require temporary safety precautions.