Objective:To investigate and understand current status of radiotherapy resources in the Association of Southeast Asian Nations (ASEAN) and analyze the radiotherapy needs of ASEAN countries, aiming to provide suggestions for China's radiotherapy technology international assistance work.Methods:We created a database of 10 ASEAN countries using open-source data, including data on population size, per capita gross national income, new cancer cases, and radiotherapy equipment (megavolt units). We also estimated the number of cases requiring radiotherapy and the demand for radiotherapy equipment. Descriptive statistics were used to present aggregate data and national data.Results:In 2020, the number of new cancer cases in ASEAN countries was 1.0992 million, and the estimated total number of cancer patients requiring radiotherapy was 700 300. The number of radiotherapy equipment required was 1 406. At present, the actual number of radiotherapy equipment in ASEAN countries is 564, and there is a certain gap between the existing radiotherapy resources in some ASEAN countries and the actual needs of cancer patients in their own countries. In 2040, the estimated number of new cancer cases in ASEAN countries will be 1.803 million, and the estimated total number of cancer patients who need radiotherapy in ASEAN countries will be 1.141 2 million. The number of required radiotherapy equipment will be 2 287. By 2040, the growth rate of radiation therapy equipment demand in ASEAN countries will be 305%, and all ASEAN countries need to allocate more radiotherapy resources to cope with the increase in the number of cancer patients and radiotherapy demand.Conclusions:ASEAN countries have a huge demand for radiotherapy in the next two decades, while there are significant differences among different countries. China's precision radiotherapy science and technology have huge potential for ASEAN countries. Radiotherapy science and technology international assistance work based on the needs of ASEAN countries will help China's radiotherapy continue to exert influence and promote the health and well-being of people in ASEAN countries.