Patent Number: 
Section: claims

1. A particle therapy apparatus comprising:a particle beam generator configured to output a particle beam having a predetermined energy;an energy degrader for reducing an energy of the predetermined-energy particle beam, the energy degrader configured to output a degraded particle beam having an energy spread that is increased with respect to an energy spread of the predetermined-energy particle beam; anda rotatable gantry including:an entrance point configured to receive the degraded particle beam in a direction substantially along a rotation axis of the gantry;a beam optic system having a plurality of dipole magnets, including a first dipole magnet and a last dipole magnet, and configured for beam transport along a beam path to a target, wherein the beam optic system is configured to have a first position along the beam path where a nominal dispersion at the first position is larger than a nominal beam size at the first position;an adjustable spread-limiting device, installed at the first position, having a spacing to limit an energy spread of the degraded particle beam and configured to output a limited beam having an energy spread that is decreased with respect to the energy spread of the degraded particle beam,wherein the spacing of the adjustable spread-limiting device is configured to be adjusted to a selected beam opening based on a selected value reflecting a maximum energy spread for the limited beam to be output by the adjustable spread-limiting device, andwherein the adjustable spread-limiting device is installed downstream of the first dipole magnet and upstream of the last dipole magnet of the plurality of dipole magnets, and there is no energy analyzer between the energy degrader and the gantry entrance point. 2. The particle therapy apparatus according to claim 1, wherein the particle beam generator is a cyclotron. 3. The particle therapy apparatus according to claim 1, wherein the adjustable spread-limiting device is located at the first position, wherein the nominal dispersion being defined as a transversal displacement of a particle whose momentum differs by 1% (one percent) of an average momentum P of all particles of the beam, the nominal beam size being defined as a one sigma beam size value of a mono-energetic particle beam having the average momentum P. 4. The particle therapy apparatus according to claim 1, wherein the rotatable gantry further comprises at least one emittance slit, emittance aperture, or emittance collimator configured to limit a transverse emittance of the particle beam to a selected maximum value. 5. The particle therapy apparatus according to claim 4, wherein the at least one emittance slit, or emittance aperture, or emittance collimator is located upstream of the adjustable spread-limiting device. 6. The particle therapy apparatus according to claim 1, wherein the spacing of the adjustable spread-limiting device is configured to be adjusted to a selected beam opening based on a predefined calibration curve that defines beam opening as a function of required energy spread. 7. The particle therapy apparatus according to claim 1, wherein the adjustable spread-limiting device has at least one aperture configured to be opened or closed in response to the selected value reflecting the target energy spread, wherein the opening or closing of the at least one aperture causes an adjustment of the spacing of the adjustable spread-limiting device. 8. The particle therapy apparatus according to claim 1, wherein the adjustable spread-limiting device includes at least one opening. 9. The particle therapy apparatus according to claim 1, wherein the adjustable spread-limiting device includes at least one spread-limiting aperture. 10. The particle therapy apparatus according to claim 1, wherein the adjustable spread-limiting device includes a collimator. 11. The particle therapy apparatus according to claim 1, wherein a distance between an output of the particle beam generator and the entry point of the rotatable gantry is less than three meters. 12. The particle therapy apparatus according to claim 1, wherein a distance between an output of the particle beam generator and the degrader is about two meters. 13. The particle therapy apparatus according to claim 4, wherein the at least one emittance slit, emittance aperture, or emittance collimator is further configured to limit a transverse emittance of the particle beam to a selected maximum value of horizontal transverse emittance and vertical transverse emittance. 14. The particle therapy apparatus according to claim 1, wherein the first dipole magnet is a 45 degree bending dipole magnet and the last dipole magnet is a 135 degree bending dipole magnet. 15. The particle therapy apparatus according to claim 1, whereinthe first dipole magnet is a 36-degree dipole magnet and the last dipole magnet is a 60-degree bending dipole magnet, andthe plurality of dipole magnets further comprises a third 66-degree bending dipole magnet located between the first dipole magnet and the last dipole magnet. 16. The particle therapy apparatus according to claim 1, wherein the energy degrader reduces the energy of the predetermined-energy particle beam by more than two-thirds. 17. The particle therapy apparatus according to claim 3, wherein the rotatable gantry further includes at least one emittance slit, emittance aperture, or emittance collimator configured to limit a transverse emittance of the particle beam to a selected maximum value and located upstream of the adjustable spread-limiting device. 18. The particle therapy apparatus according to claim 17, wherein the spacing of the adjustable spread-limiting device is configured to be adjusted to a selected beam opening based on a predefined calibration curve that defines beam opening as a function of required energy spread. 19. The particle therapy apparatus according to claim 18, wherein a distance between an output of the particle beam generator and the degrader is about two meters.