A method to accurately and rapidly locate tumor, comprising the steps of using a immobilization module to ensure the consistency of patient positioning, verification and the position of each treatment using a locating and marking module comprising a locating and marking tool for locating and marking using a data input module to obtain the data required for a calculation of Optical Positioning System in radiotherapy and using a positioning module to calculate the deviation between the planned isocenter and the machine isocenter, and to provide prompts of patient positioning.
