Organs at Risk

Organs at risk are healthy organs or tissues near a radiation-treatment target whose exposure must be limited to reduce treatment-related harm.

Radiation Dose: The amount of ionizing radiation absorbed by matter, measured in grays. Dose to an organ at risk is the quantity planners seek to constrain.
Radiation Therapy: The use of ionizing radiation to control or destroy cancer and some other diseases. Organs at risk are defined in relation to a radiation treatment plan.
Radiation Therapy for Prostate Cancer: The use of radiation to control prostate cancer, delivered externally or with implanted sources. The rectum and bladder are commonly protected during prostate treatment.
Radiation Pneumonitis: Inflammation of lung tissue that can develop after radiation exposure. It is a potential complication when lung dose exceeds tolerable levels.
Dose–Volume Histogram: A graph showing how much of a structure receives at least each radiation dose. It summarizes how a planned dose is distributed across an organ at risk.
Radiation Therapy Planning Image: Medical imaging used to map treatment targets and nearby anatomy for radiation planning. Images reveal which healthy structures lie close enough to require protection.
Radiation Therapy for Lung Cancer: The treatment of lung cancer with focused external-beam radiation, sometimes combined with other therapies. The lungs, heart, esophagus, and spinal cord can constrain thoracic treatment plans.
Radiation-Induced Myelopathy: Spinal-cord injury caused by exposure to therapeutic or other ionizing radiation. The spinal cord’s sensitivity makes its dose a strict planning concern.
Radiotherapy Treatment Planning: The process of designing radiation delivery to treat a target while limiting exposure to healthy tissue. Planners balance target coverage against dose constraints for nearby organs.
Radiation Therapy Contouring: The outlining of targets and normal structures on medical images for treatment planning. Contouring gives each organ at risk a defined shape for dose calculation.

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