Patent Number: 
Section: claims

1. A radiotherapy apparatus comprising:a source of radiation configured to emit a beam of radiation; anda collimator structure configured to limit a lateral extent of the beam, the collimator structure comprising:a primary collimator positioned adjacent to the radiation source, the primary collimator comprising a primary aperture configured to shape the beam;a first collimator comprising a plurality of adjacent elongate leaves, the leaves being extendable into the beam in a first direction transverse to the beam; anda block collimator positioned away from the radiation source, the block collimator comprising a spine region extending in a second direction and an aperture, located on the spine region, configured to permit the beam to pass through, the block collimator being extendable into the beam in the second direction transverse to the beam and transverse to the first direction. 2. The radiotherapy apparatus according to claim 1, wherein the aperture is cone-shaped. 3. The radiotherapy apparatus according to claim 1, wherein the aperture is a through-hole. 4. The radiotherapy apparatus according to claim 1, wherein the aperture is filled with a radiotransparent material. 5. The radiotherapy apparatus according to claim 4, wherein the aperture has a frusto-conical shape configured to limit the beam to a desired diameter. 6. The radiotherapy apparatus according to claim 1, wherein the block collimator includes a plurality of apertures including the aperture and at least one additional aperture. 7. The radiotherapy apparatus according to claim 6, wherein the plurality of apertures have different dimensions. 8. The radiotherapy apparatus according to claim 6, further comprising:a control apparatus configured to, in a first mode:extend the block collimator such that the aperture is placed in the path of the beam; andextend leaves of the first collimator in order to cover the at least one additional aperture. 9. The radiotherapy apparatus according to claim 1, further comprising:a control apparatus configured to, in a first mode, extend leaves of the first collimator in order to cover the aperture. 10. The radiotherapy apparatus according to claim 9, wherein the control apparatus is further configured to, in a second mode:extend the block collimator such that the aperture is placed in the path of the beam. 11. The radiotherapy apparatus according to claim 1, wherein the block collimator further comprises:a first side region and a second side region flanking the spine region, the first and second side regions having a second thickness that is less than the first thickness. 12. The radiotherapy apparatus according to claim 11, wherein the block collimator further comprises:a front edge portion having the first thickness. 13. The radiotherapy apparatus according to claim 1, wherein the block collimator further comprises:a frontal portion extending transversely to the spine region in either direction to define a T shape. 14. The radiotherapy apparatus according to claim 13, wherein the frontal portion extends in the first direction. 15. The radiotherapy apparatus according to claim 13, wherein the spine region is of a first thickness and the block collimator further comprises:a first side region and a second side region flanking the spine region, the first and second side regions having a second thickness that is less than the first thickness. 16. A collimator structure for a radiotherapy apparatus, the collimator structure comprising:a primary collimator comprising a primary aperture configured to shape a beam of radiation emitted from a source of radiation, the primary collimator being positioned adjacent to the radiation source;a first collimator comprising a plurality of adjacent elongate leaves, the leaves being extendable into the beam in a first direction transverse to the beam; anda block collimator positioned away from the radiation source, the block collimator comprising a spine region extending in a second direction and an aperture, located on the spine region, configured to permit the beam to pass through, the block collimator being extendable into the beam in the second direction transverse to the beam and transverse to the first direction. 17. The collimator structure according to claim 16, wherein the block collimator comprises a plurality of apertures having different dimensions. 18. The collimator structure according to claim 16, wherein the aperture has a frusto-conical shape configured to limit the beam to a desired diameter. 19. The collimator structure according to claim 16, wherein the spine region has a first thickness and the block collimator further comprises:a first side region and a second side region flanking the spine region, the first and second side regions having a second thickness that is less than the first thickness. 20. The collimator structure according to claim 19, wherein the block collimator further comprises:a front edge portion having the first thickness.