A particle beam radiotherapy system has been proposed by using a set of first and second scatterers, whereby a short-duration pulse beam is irradiated to a lesion. When the duration of the radiotherapy beam is 200 milliseconds or less, healthy tissues are selectively protected and only cancer tissues are damaged. For example, it can be used for cancer treatment of brain metastases that may be distributed throughout the entire brain tissues. The positions of the scatterers and the energy of the incident particle beams are optimized according to the position and the volume of the brain tissues.