Total central radiotherapy, also known as whole brain and whole spinal cord radiotherapy (CSI), is an important treatment for disseminated central nervous system tumors. Its irradiation range includes the whole brain and all spinal cord, and has the characteristics of long target area, large position fixation range, poor patient autonomy and poor positioning repeatability[1]。 The irradiation field range of conventional accelerator is only 40 cm ×40 cm, and the insufficient irradiation field range can only be solved by connecting multiple irradiation fields in multiple centers. Radiotherapy workers have been exploring ways to solve the uneven dose distribution in the target area at the junction of irradiation fields and the cold and hot dose problems formed in the actual irradiation process. Most of the existing measures can only solve the problems of uneven dose distribution and poor conformity in the target area or find better positioning methods to improve the positioning accuracy[2,3,4,5]All measures are not obvious enough to reduce the positioning risk. The purpose of this study is to find a CSI planning field convergence method that can significantly reduce the dose cold and hot spots caused by positioning error, so as to meet the clinical CSI dosimetry requirements.