I. Why choose image-guided three-dimensional precision radiotherapy (IGRT)? Radiotherapy is one of the three traditional means of malignant tumor treatment and occupies an important position in the comprehensive treatment of malignant tumors, and many cancer patients need to receive radiotherapy at some stage of treatment. With the rapid development of computer technology, medical imaging technology, image processing technology, and the continuous updating of radiotherapy equipment, radiotherapy technology has evolved from two-dimensional general radiotherapy to three-dimensional conformal radiotherapy, intensity-modulated conformal radiotherapy, and image-guided precise stereotactic radiotherapy (IGRT), which significantly improves the effect of radiotherapy and greatly reduces the damage to normal tissues, thus significantly improving the quality of life of patients. Especially, image-guided radiotherapy has been evaluated by experts at home and abroad as a change in the history of radiation oncology, and is the mainstream of radiotherapy technology in the 21st century, which is only carried out by a few units in China at present. Conventional conformal and intensity-modulated radiotherapy has the following problems: 1. The patient’s positional shift in the whole treatment process during fractionated radiotherapy, and it is found that sometimes this shift is even greater than 1.5 cm, which may shift the tumor tissue to be treated out of the treatment target area and make the whole treatment fail; at the same time, excessive positional shift may include too many surrounding normal tissues, which can cause fatal Injury. 2. A complete radiotherapy process may take about 2 months, with the course of treatment, the patient’s appearance will change, and the relative position of body markers will also change, which will cause serious deviation of the treatment target area. Again, as radiotherapy continues, the tumor will gradually shrink and deform, and the relative positions of the target area and important normal tissues and organs will change, so that the initially designed treatment plan will be inconsistent with the actual situation of the tumor, and the critical organs near the irradiation field may be irradiated with a higher dose at this time, which will bring about unnecessary injuries. 3, no matter the tumor and the adjacent normal tissues will be affected by respiration and peristalsis of the cavity organs, and it is impossible to monitor and adjust this error in the process of conventional radiotherapy. How to eliminate the effect of physiological movement of organs in radiotherapy, such as respiratory movement, bladder filling, small bowel peristalsis, tumor increase and decrease, and elastic deformation of organs, etc., is the hotspot of the current radiotherapy research, which is mainly due to the fact that the error brought about by this aspect is much larger than that of posing error. Advantages of image-guided three-dimensional precision radiotherapy (IGRT) There are systematic and random errors in precision radiotherapy for tumors, which are simply due to the positional differences caused by the technician’s positioning status during each treatment and the changes in the patient’s anatomical position during the fractionated treatments, such as respiratory movements, bladder filling, small bowel movement, thoracic and abdominal fluid, and tumor enlargement or shrinkage, and so on. Despite the use of a variety of auxiliary positioning devices and strict accordance with the operating procedures, the positioning error may still be several millimeters or even greater, which is more obvious in conformal and intensity-modulated radiotherapy. Wang Yinhua, Department of Radiotherapy, Wuhu Second People’s Hospital In recent years, diagnostic cone-beam CT (CBCT) has been installed on a linear gas pedal, which has become a cutting-edge radiotherapy equipment that integrates CT and linear gas pedal, and realizes image-guided precision radiotherapy [IGRT], which refers to scanning a three-dimensional image of a certain volume of the tumor target area and its surroundings with CBCT before each radiotherapy treatment and compare it to the image of the treatment plan. If an error is found, the patient’s position is adjusted so that the tumor target area is returned to the treatment plan position, and the irradiation field completely “follows” the treatment target area. Image-guided precision radiotherapy is the most advanced tumor radiotherapy technology in the world, which allows patients to obtain accurate images of the patient’s position, vital organs and anatomical location of the tumor in the actual position of the tumor radiotherapy, and through real-time on-line correction and revision of the radiation treatment plan, the patient receives the most accurate radiation treatment every time. Image-guided radiotherapy, on the basis of 3D conformal and intensity-modulated radiotherapy, further improves the accuracy of radiation irradiation, which can maximally protect normal tissues under the premise of ensuring sufficient irradiation of tumors, thus significantly improving the radiotherapy and cure rate of tumor patients while improving the quality of life. The following is an example of common nasopharyngeal cancer to introduce the whole process of image-guided radiotherapy carried out in our center. I. CT scanning: The patient takes the supine position, the head, neck and shoulder thermoplastic mold for fixing the patient’s position is given to the patient to wear, the treatment bed is moved through the laser light in the treatment room, and the marking line in the treatment center is aligned, so that the patient is outside of the treatment position. Then a metal marker lead bead is attached to the treatment center, and then the treatment bed is rotated 180°, and the patient is sent into CTVision’s unique 82CM large-aperture CT for scanning. Acquiring images: The doctor determines the scope of CT scanning according to the anatomical structure of the patient, the location, scope and size of the lesion, and then adjusts the scanning layer thickness, layer spacing and other parameters to obtain the image information from the scanning. The acquired images are then reconstructed and transmitted to the image alignment workstation. Image Alignment: The physicists will transmit the reconstructed CT images to the workstation by using metal markers and specific software in the three vertical planes of cross-sectional, coronal and sagittal planes, according to the reference information of the external contour, bony markers and the range of the target area, and then by translating and rotating certain anatomical structures to make them match with the images of the treatment plan, in order to realize the calibration of the two images. IV. Adjustment of Positioning: After the image alignment is completed, the IGRT system will automatically calculate the displacement in the three-dimensional spatial direction between the isocenter and the accelerated treatment center within the treatment plan. After the doctor’s confirmation, the technician will re-adjust the treatment bed according to the displacement data derived from the alignment to make the treatment plan position consistent with the actual treatment position and then start the radiation therapy. Image-guided three-dimensional precision radiotherapy (IGRT) represents the highest level of current radiotherapy Radiation therapy is one of the three major means of treating tumors, and image-guided intensity-graded radiation therapy is recognized as a revolutionary advancement in the more than 100-year history of radiation therapy. During the course of radiation therapy, all organs of the human body (including tumor tissues) are in constant motion all the time. For example, breathing, heartbeat, and gastrointestinal peristalsis all affect the position and shape of the tumor. In addition, there is a certain change in the patient’s position during each treatment, and this change will also lead to a change in the position of the tumor. Therefore, there is always a certain deviation in radiation therapy, and IGRT technology is the best means to correct these deviations, which utilizes CT imaging to track the effects of the patient’s position change, breathing, heartbeat, etc. on the tumor position, and by correcting the error, the radiation will be focused on the tumor tissue, reducing the amount of radiation received by the normal tissues, reducing the side effects, and improving the efficacy of the treatment.The specific implementations of IGRT technology include There are online calibration, adaptive radiotherapy, breath-holding, respiratory gating, four-dimensional radiotherapy technology and real-time tracking technology. Real-time tracking technology can detect and track the motion of target area caused by various reasons in real time, which represents the ideal realm of radiotherapy. IGRT solves the problem of accurate conformal treatment of moving targets, which improves geometric accuracy while reducing the amount of normal tissue received. IGRT has been shown to reduce treatment error and normal tissue exposure volume in the vast majority of cases.IGRT is generally applicable to a wide range of tumors that can be treated with conventional radiotherapy, but it is better suited to clinical situations that would benefit more from IGRT, including: tumors in close proximity to sensitive normal tissues, tumors with a controlled dose that is much higher than the tolerance of the neighboring normal tissues, tumors with very severe consequences of positional errors, and tumors with large errors of organ displacement. The tumor may have a large margin of error for organ displacement and recurrent tumors. For example, nasopharyngeal carcinoma, laryngeal carcinoma, tonsil carcinoma, paranasal sinus carcinoma and parotid adenocarcinoma in the head and neck region, intracranial metastases, gliomas, pituitary tumors, meningiomas and other tumors of the central nervous system, lung, esophageal, breast and mediastinal benign and malignant tumors, pancreatic carcinoma, hepatocellular carcinoma, gastric cancer, cervical carcinoma, prostatic carcinoma, rectal cancer, anal carcinoma, sarcoma and other malignant tumors of the abdomen, as well as hemangiomas located in the spinal column, bone metastasis and tumors of nerve origin. Nowadays, radiation therapy has entered a new era of precise positioning, precise planning and precise treatment, and IGRT will make great contributions to controlling tumors, reducing side effects and improving patients’ quality of life.