Patent Number: 051480328
Section: claims

1. A radiation emitting device for irradiating an object with a radiation beam, said radiation emitting device comprising: a radiation source for generating a radiation beam, said source including a pulse generating unit for generating pulses and wherein variation of the pulse repetition frequency of said pulses varies the dose rate of said radiation beam;  an aperture plate arrangement located in the trajectory of said radiation beam between said radiation source and said object and including a plurality of plates for determining a radiation field at said object;  a drive control unit coupled to said aperture plate arrangement for moving at least one plate of said plurality of plates at a constant speed;  a dose rate measuring unit located in the trajectory of said radiation beam for measuring the dose rate of said radiation beam; and  a dose control unit coupled to said radiation source, said dose rate measuring unit and to said drive control unit for varying the pulse repetition rate of said pulses, and hence the dose rate of said radiation beam during irradiation in correlation with the movement of said plate at constant speed.  said dose rate controller includes means for providing preset values of dose rate for said radiation beam in correlation with movement of said at least one plate of said aperture plate arrangement.  during movement of said aperture plate said dose rate control unit calculates the deviation between said preset values of dose rate and measured values of dose rate provided by said dose rate measuring unit, for providing a control signal to said pulse control unit which controls its pulse repetition frequency.  a drive unit coupled to move said plate;  a sensing device coupled to said plate for sensing its position; and  a motor controller coupled to said drive unit and said sensing device for controlling the movement of said plate in a predetermined manner. 2. The radiation emitting device according to claim 1, wherein: 3. The radiation emitting device according to claim 2, wherein: 4. A radiation emitting device according to claim 3, wherein said pulse control unit generates trigger pulses, and wherein said dose control unit generates signals for varying the pulse repetition frequency of said trigger pulses in correlation with the movement of said plate. 5. A radiation emitting device according to claim 1, wherein said drive control unit comprises: