Intensity-modulated radiation therapy is a 3-dimensional conformal radiation therapy planning and delivery tool that shapes the radiation dose distribution and minimizes the dose to normal structures. Intensity-modulated radiation therapy implies inverse planning algorithms (i.e., the physician determines radiation treatment parameters to maximize dose to the target and minimize dose to normal tissues, and the planning algorithm maximizes the adherence to these parameters by modifying the beam spatially and/or temporally). Spatial and temporal beam modification is often achieved by dynamically moving multi-leaf collimators. Intensity-modulated radiation therapy can also be achieved via custom-made beam compensators, which are derived from inverse planning algorithms. A novel way to deliver intensity-modulated radiation therapy is tomotherapy, in which a bank of collimated leaves shutter open and closed while rotating around the patient in a spiral manner. The unifying principle of all intensity-modulated radiation therapy planning and delivery methods is inverse planning. Intensity-modulated radiation therapy results in a greater deposition of low doses to normal tissue, which may increase the risk of second malignancies. Also called IMRT.