Patent Number: 
Section: claims

1. An image-guided radiation therapy (IGRT) apparatus, comprising:a medical imaging device integrated with a linear accelerator, the linear accelerator configured for emitting a radiation beam which is shaped by a beam shaper; anda gantry configured to rotate the emitted radiation beam about an axis,wherein the beam shaper is mounted to an adjustment arm configured to adjust the beam shaper between a first position and a second position, andwherein the medical imaging device is an MRI device generating a magnetic field, and the second position is a radial distance away from the magnetic field such that a magnetic field strength generated by the MRI device at the second position is lower than a magnetic field strength generated by the MRI device at the first position. 2. The IGRT apparatus as claimed in claim 1, wherein the first position is a treatment position, and the second position is a service position. 3. The IGRT apparatus as claimed in claim 1, wherein the position of the linear accelerator is moveable with the beam shaper between the first and second positions. 4. The IGRT apparatus as claimed in claim 1, wherein the beam shaper is a multi-leaf collimator. 5. The IGRT apparatus as claimed in claim 1, wherein the adjustment arm is connected to a fixed body through a linkage and operable to move the beam shaper between the first and second positions. 6. The IGRT apparatus as claimed in claim 5, wherein the fixed body is integral with the gantry, and wherein the linkage comprises a pivot operable to pivot the beam shaper from a position within the gantry to a position removed from the gantry. 7. The IGRT apparatus as claimed in claim 5, further comprising an actuator to move the adjustment arm between the first and second positions. 8. The IGRT apparatus as claimed in claim 7, wherein the actuator comprises a pneumatically or hydraulically operated component. 9. The IGRT apparatus as claimed in claim 8, wherein the actuator comprises at least one electro-mechanical actuator. 10. The IGRT apparatus as claimed in claim 9, further comprising a gearing system. 11. The IGRT apparatus as claimed in claim 5, wherein the linkage comprises a multi-axis joint. 12. The IGRT apparatus as claimed in claim 5, further comprising a locking mechanism for locking the beam shaper into position during delivery of radiation treatment. 13. The IGRT apparatus as claimed in claim 5, wherein the adjustment arm is provided with one or more joints operable to present the beam shaper in an increased number of positions and orientations. 14. The IGRT apparatus as claimed in claim 5, wherein the adjustment arm incorporates a linear actuator allowing the length of the arm to be adjusted thereby providing further flexibility in the positioning of the beam shaper when removed from the operational position. 15. The IGRT apparatus as claimed in claim 1, wherein the IGRT apparatus has a closed drum configuration. 16. The IGRT apparatus as claimed in claim 1, wherein the IGRT apparatus has an open ring configuration. 17. A radiation therapy apparatus for delivering radiation therapy to a target, the apparatus comprising:a linear accelerator configured to emit, via a radiation beam emitter, a radiation beam along a beam path toward the target;an imaging device configured to obtain an image of the target;a beam shaper configured to shape the emitted radiation beam emitted toward the target;a gantry coupled to the linear accelerator, wherein the gantry is configured to rotate the radiation beam emitter about an axis; andan adjustment arm connected to the gantry and to the beam shaper, wherein the adjustment arm is configured to adjust the beam shaper between a treatment position and a non-treatment position, andwherein the medical imaging device is an MRI device generating a magnetic field, and the non-treatment position is a radial distance away from the magnetic field such that a magnetic field strength generated by the MRI device at the non-treatment position is lower than a magnetic field strength generated by the MRI device at the treatment position. 18. The radiation therapy apparatus as claimed in claim 17, wherein the adjustment arm is connected to a fixed body through a linkage and operable to move the beam shaper between the treatment and non-treatment positions. 19. The radiation therapy apparatus as claimed in claim 18, wherein the fixed body is integral with the gantry, and wherein the linkage comprises a pivot operable to pivot the beam shaper from a position within the gantry to a position removed from the gantry. 20. The radiation therapy apparatus as claimed in claim 17, wherein the imaging device has an open ring configuration.