The present invention relates to a particle of a radiation device (1) for radiotherapy comprising at least one detector (2) and at least one analyzer (7) capable of detecting a single gamma ray particle (4). An apparatus and method for monitoring the range of radiation (3), upon detection of gamma-ray particles (4), represented below as events, a signal is generated in the detector (2), The analyzer (7) analyzing the signal of the detector (2) detects all events or selected events, the signal being correlated in time with the arrival of gamma ray particles (4) in the detector (2) A single particle from the radiation device (1) to the outside of the radiation device (1), assigned to the time, with the radiation device (1) or a separate particle detector (8) having a time uncertainty of 10 nsec or less Or provide a reference signal that correlates with the appearance of the particle bunch and The particles or particle bunches that generated the gamma ray particles (4) detected by the detector (2), represented as gar particles or particle bunches, have a reference plane perpendicular to the beam direction of the radiation device (1). The time passed is obtained from the reference signal for all or selected events in the analyzer (7), the time of detection of the gamma ray particles (4) in the detector (2), and the event trigger particles or particle bunches The time difference between the time that passes through the reference plane is calculated for all or selected events in the analyzer (7), and at least one statistic of the time difference, represented below as the time distribution (6) Treatment (6) is obtained in the analyzer (7), the time distribution (6) is analyzed, information about the range of the particle beam (3) is obtained therefrom, and the treatment of the treatment monitored by the device Plan with The notification about 致性, characterized in that can be obtained from primarily time distribution (6), to an apparatus and method.本発明は、単一のガンマ線粒子（４）を検出することが
