Three-dimensional conformal intensity modulated radiotherapy (IMRT): The three-dimensional conformal intensity modulated radiotherapy (IMRT) technology is based on the three-dimensional conformal radiotherapy (3D-CRT), using computerized three-dimensional inverse treatment planning (Inverse Planning) and CT simulation positioning, 3D image reconstruction technology, by changing the intensity of radiation in the target area, so that any point in the target area can get the ideal By varying the radiation intensity in the target area, the ideal dose can be obtained at any point in the target area, and at the same time, the dose to the vital organs can be limited to the tolerable range according to the doctor’s requirements, so that the dose to the normal tissues immediately outside the target area can be minimized. This ideal dose calculation is achieved through a 3D treatment planning system with inverse calculation capabilities. The precise positioning of the target area is a prerequisite for IMRT, which is achieved through a CT simulator with 3D image processing. Three-dimensional conformal intensity modulated radiotherapy technology is the symbol of modern radiotherapy entering “precise positioning, precise design, precise treatment” and can further improve the gain ratio of tumor radiotherapy. This high-precision radiotherapy technology has brought tumor radiation therapy into a new era. IMRT is mainly applied to nasopharyngeal cancer, paranasal sinus tumors, tumors near the spinal cord or brainstem, intracranial irregular benign and malignant tumors, prostate cancer, breast cancer after breast-conserving surgery, rectal cancer, lung cancer, esophageal cancer, etc.