It is well-known that radiation dose is accumulated. However, in clinics patient is usually asked to take a series of radiographs including panoramic, lateral and posteroanterior radiographs, sometimes even a CBCT or CT scan in a very short period for orthodontic or orthognathic treatment planning and/or prognosis evaluation. Thus, whether the radiation dose accumulated in such a short time increases potential cancer risk becomes concern. The lecture aims to present a series of studies investigating the potential biological damage on such patients and provide a theoretical basis for the optimization of treatment process and radiation protection.