Intensity-Modulated Radiotherapy

Intensity-modulated radiotherapy, or IMRT, is an advanced form of external beam radiotherapy that uses computer-controlled linear accelerators to shape the radiation dose to the three-dimensional form of a tumor. It works by modulating the intensity of the radiation beam across many small segments, raising the dose delivered to the tumor itself while reducing or avoiding dose to the surrounding healthy tissue, an improvement over earlier three-dimensional conformal radiotherapy that is especially useful for tumors that wrap around sensitive structures such as the spinal cord. It is used for complex treatment sites including cancers of the central nervous system, head and neck, prostate, breast and lung, and it is commonly paired with image-guided radiation therapy, which verifies the position of the patient and the tumor before and during treatment to keep the higher-precision dose on target.