ABSTRACT
Shortly after the discovery of X-rays by Wilhelm Röntgen in 1895 (Nitske 1971), it was found that X-rays could be used not only for imaging but also for treating disease. One of the earliest clinical examples was to use X-rays to treat skin malignancies (Freund 1904). Although the mechanism involved in using X-rays to treat malignancies is very complex (Hall 1994), clinical evidence has shown that the use of X-rays, or more generally, radiation to treat cancer (now known as radiation therapy) is effective for a large number of cancer patients. Radiation therapy has now become one of the main treatment modalities for cancer patients (Holleb et al.1991).
