Schematic diagram of a laser-proton therapy unit.
Schematic description of the proton selection system. Protons are produced right before the primary collimator and travel in a magnetic field distributed in four separated regions. The desired protons move initially toward axis, deflect in the field, and return to axis after traversing the magnetic field. Those unwanted particles are either stopped by the stoppers and collimators, or absorbed by the surrounding shielding.
Ideal step field used particle selection.
Single rectangular loop located at . The length in the axis is , while it is in the axis.
Field distributions for a single loop shown in Fig. 4, whose size is defined by ( axis) and ( axis). (a) at for different positions in the axis; (b) at for different positions in the axis; (c) a comparison between , , at , .
Schematic description of a rectangular solenoidal superconducting magnet. A NbTi wire wound with a number of turns carries a current and produces a magnetic field . The dimensions are given by , and ,. The thickness in both and axis is . is the gap between the paired magnets.
Field distributions for a pair of superconducting solenoids with , , and . The thickness is 0.2 cm and the gap between the magnets along the axis is 1 cm. (a) for different at ; (b) for different at ; (c) a comparison between , , at , .
Field distrbutions from a four-magnet system. (a) for different at . The field does not change much in the direction. (b) for different at . The field does not change much in the direction for less than 15 cm within the magnet region. (c) A comparison between , , at , .
Trajectories of protons for different kinetic energies. (a) . The distance between 250-MeV protons an 220-MeV protons is about 0.45 cm in the middle of the particle selection system while the distance between the 190- and 160-MeV protons is about 0.7 cm. (b) . The distance between 250-MeV protons and 160-MeV protons is about 0.3 cm in the middle of the particle selection system while the distance between the 160- and 70-MeV protons is about 0.8 cm.
Proton trajectories for different gap, , and the width for the middle magnets is . (a) , (b) . (c) . (d) . (b) Gives the best refocus.
Proton trajectories for different widths of the middle magnets. (a) . Protons refocus above the beam axis and at different positions for different energies; (b) . Protons come down across the beam axis and pass through different positions on the axis for different energies. The best result is which is shown in Fig. 10(b).
Comparison of proton trajectories between the ideal step field and realistic magnet-produced field.
Energy spectra for selected energies. (a) The spectra for the magnet-generated field and step field. . (b) The spectra only for the magnet-generated field. .
Dose distributions in the ideal step field and realistic magnet-produced field for the proton beams selected at different energies.
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