Patent Number: 
Section: claims

1. An attenuator system for attenuating a radiation beam, comprising:a first attenuating element placed in a path of a radiation beam for attenuation thereof;a second attenuating element also placed in said path of said radiation beam so as to form an attenuation cascade with said first attenuating element;a first positioner operatively connected to said first attenuating element, which moves said first attenuating element along a first direction; anda first processor operatively connected to said first positioner for controlling motion of said first attenuating element;wherein a two-dimensional attenuation distribution of said first attenuating element varies linearly with respect to at least one coordinate, and wherein one of said first and second attenuating elements has two portions with different slopes and cross-sections. 2. The attenuator system according to claim 1, wherein a two-dimensional attenuation distribution of said second attenuating element varies linearly with respect to at least one coordinate. 3. The attenuator system according to claim 1, wherein said first and second attenuating elements form an attenuating cascade, wherein the attenuating cascade has an attenuation distribution depending on a position of said first attenuating element. 4. The attenuator system according to claim 3, wherein the attenuation distribution of the attenuating cascade is generally uniform over an area equal to a cross-section of the radiation beam for a range of positions of said first attenuating element. 5. The attenuator system according to claim 1, further incorporating a second positioner operatively connected to said second attenuating element, which moves said second attenuating element along a second direction; and a second processor operatively connected to said second positioner for controlling motion of said second attenuating element. 6. The attenuator system according to claim 5, wherein said first direction and said second direction are parallel to each other. 7. The attenuator system according to claim 5, wherein said first direction and said second direction are both perpendicular to said radiation beam. 8. The attenuator system according to claim 1, wherein said first attenuating element has a cross-section coplanar with the radiation beam which is triangular in shape and which has an apex with a positive angle slope, and said second attenuating element has a portion with a cross-section coplanar with the radiation beam which is triangular in shape and which has an apex with a negative angle slope. 9. The attenuator system according to claim 8, wherein magnitudes of the positive and negative angle slopes are equal. 10. The attenuator system according to claim 1, further comprising a radiation sensor that senses attenuated radiation that passes through said first and second attenuating elements, said radiation sensor being in operative communication with said first processor, wherein temporal beam modulation is carried out by sensing a beam intensity drift with said radiation sensor and compensating by moving said first attenuating element by said first positioner. 11. The attenuator system according to claim 1, wherein said first and second attenuating elements have cross-sections that vary along a Cartesian coordinate. 12. The attenuator system according to claim 1, wherein said first and second attenuating elements have cross-sections that vary along a polar coordinate. 13. A radiotherapy system comprising:a radiation beam source which emits a radiation beam;a first attenuating element placed in a path of the radiation beam for attenuation thereof;a second attenuating element also placed in said path of said radiation beam so as to form an attenuating cascade;a first positioner operatively connected to said first attenuating element, which moves said first attenuating element along a first direction; anda first processor operatively connected to said first positioner for controlling motion of said first attenuating element;wherein a two-dimensional attenuation distribution of said first attenuating element varies linearly with respect to at least one coordinate, and wherein one of said first and second attenuating elements has two portions with different slopes and cross-sections. 14. The radiotherapy system according to claim 13, further comprising a radiation sensor that senses attenuated radiation that passes through said first and second attenuating elements, said radiation sensor being in operative communication with said first processor, wherein temporal beam modulation is carried out by sensing a beam intensity with said radiation sensor and moving said first attenuating element with said first positioner. 15. A method for attenuating a radiation beam, comprising:placing a first attenuating element in a path of a radiation beam for attenuation thereof;placing a second attenuating element also in said path of said radiation beam so as to form an attenuating cascade; andmoving said first attenuating element along a first direction;wherein a two-dimensional attenuation distribution of said first attenuating element varies linearly with respect to at least one coordinate, and wherein one of said first and second attenuating elements has two portions with different slopes and cross-sections. 16. The method according to claim 15, comprising forming an attenuating cascade with said first and second attenuating elements form, whereas a second positioner is operatively connected to said second attenuating element, which moves said second attenuating element along a second direction; and a second processor is operatively connected to said second positioner for controlling motion of said second attenuating element; and wherein the attenuating cascade has an attenuation distribution depending on a position of said first attenuating element. 17. The method according to claim 15, further comprising carrying out temporal beam modulation by sensing a beam intensity and moving at least one of said first and second attenuating elements.