The time required for a course of radiotherapy needs to be defined according to the specific situation. There are many factors affecting the duration of radiotherapy, mainly including the purpose of radiotherapy, the site of radiotherapy and the mode of radiotherapy. 1. Purpose of radiotherapy: according to the purpose of treatment, radiotherapy can be categorized into various modes. Among them, radical radiotherapy is more difficult to treat and takes a relatively long time, roughly 6-7 weeks; preoperative radiotherapy is mainly for preparation, a course of about 4 weeks; postoperative radiotherapy is for consolidation of treatment, a course of about 5 weeks; palliative radiotherapy takes about 4-5 weeks for a course of treatment. 2. Radiotherapy site: the time needed for the general course of radiotherapy varies with different radiotherapy sites, for example, radical radiotherapy for esophageal cancer takes about 7-8 weeks, while whole brain radiotherapy takes about 3 weeks. 3. Radiotherapy modes: there are also differences in the duration of treatment between different radiotherapy modes, the above mentioned is conventional segmented radiotherapy, while high-dose segmented mode has shorter treatment time. Taking lung cancer as an example, conventional segmentation usually takes about 7 weeks, while stereotactic body radiotherapy (SBRT) can be completed in about 1 week. Due to the difference in tolerance of individuals, the exact duration of radiotherapy should be based on the individual’s physical condition, and if serious discomfort occurs during radiotherapy, the physician should be informed in time so that the radiotherapy program can be adjusted.