Concept of three-dimensional conformal radiotherapy and intensity modulated radiotherapy With the continuous improvement of diagnostic imaging and radiotherapy technology, the use of high-energy X-rays or gamma rays, electron beams, proton beams and other continuous rotation around the target or fixed-field cluster irradiation can obtain a dose distribution conformal to the tomogram of the target area at the irradiation site, so that the radiation is maximally concentrated in the lesion target area. When treating a patient, the intensity distribution in the direction of radiation exposure is first calculated using a planning system based on the three-dimensional anatomy of the lesion (target area) and surrounding organs and tissues obtained from CT and MRI, and then the treatment is performed on the treatment machine according to the designed intensity distribution. This method is called conformal radiation therapy, which means that the morphology of the high radiation dose area (irradiation field) is consistent with the morphology of the tumor (target area). Since the target area is always three-dimensional and is treated with radiation, it is also called three-dimensional conformal radiation therapy. When uniform dose distribution within the target area and on the target surface is required for conformal therapy, it is necessary to make the dose rate within each irradiation field adjustable as required and make the dose in the target area very high and the dose in the surrounding tissues very low, which is called intensity modulated radiotherapy Peacock system: the dose distribution in the plane of the irradiation field is shaped like an open peacock, and the key technology is the multileaf collimator (MIMIC) and the inverse treatment plan design system. The system starts from the dose prescribed by the doctor to the tumor and the allowed irradiation amount of the surrounding normal tissue, reverse the plan and control the multi-leaf collimator for treatment. Tomotherapy: An intensity-modulated conformal radiotherapy device that integrates a CT machine with a linear gas pedal, proposed by Professor Mackie of the University of Wisconsin in 1993. The main features are: ① the patient and the treatment beam move simultaneously, forming a spiral high-dose distribution area in the target area, without the problems of overdose (hot spot) produced by the overlap between layers of intensity-modulated conformal radiotherapy irradiation and underdose (cold spot) produced by the separation between layers; ② CT scan positioning and irradiation treatment are performed simultaneously, fundamentally solving the problem of repeated positioning accuracy of fractionated treatment.