Radiotherapy (RT) has played important roles in cancer treatment for more than one century. The development of RT techniques allows high-dose irradiation to tumors while reducing the radiation doses delivered to surrounding normal tissues. However, RT is a complex process and involves understanding of the principles of medical physics, radiobiology, radiation safety, dosimetry, radiation treatment planning, simulation and interaction of radiation with other treatment modalities. Each step in the integrated process of RT needs quality control and quality assurance (QA) to prevent errors and to ensure that patients will receive the prescribed treatment correctly. The aim of this study is to help the radiotherapists in identifying a system for QA that balances patient safety and quality with available resources. Recent advances in RT focus on the need for a systematic RTQA program that balances patient safety and quality with available resources. It is necessary to develop more formal error mitigation and process analysis methods, such as failure mode and effect analysis (FMEA), to focus available QA resources optimally on the process components. External audit programs are also effective. Additionally, Clinical trial QA has a significant role in enhancing the quality of care. The International Atomic Energy Agency (IAEA) has operated both an on-site and off-site postal dosimetry audit to improve practice and to assure the dose from RT equipment. Both postal dosimetry audit and clinical trial RTQA, especially for advanced technologies, in collaboration with global networks, will serve to enhance patient safety and quality of care.