Prog Med Phys.  2015 Mar;26(1):12-17. 10.14316/pmp.2015.26.1.12.

Monte Carlo Simulation of the Carbon Beam Nozzle for the Biomedical Research Facility in RAON

• Bae JB
• Cho BC
• Kwak JW
• Park WY
• Lim YK
• Chung HT

• KMID: 2315773
• DOI: http://doi.org/10.14316/pmp.2015.26.1.12

Abstract

The purpose of the Monte Carlo simulation study was to provide the optimized nozzle design to satisfy the beam conditions for biomedical researches in the Korean heavy-ion accelerator, RAON. The nozzle design was required to produce C12 beam satisfying the three conditions; the maximum field size, the dose uniformity and the beam contamination. We employed the GEANT4 toolkit in Monte Carlo simulation to optimize the nozzle design. The beams for biomedical researches were required that the maximum field size should be more than 15x15 cm2, the dose uniformity was to be less than 3% and the level of beam contamination due to the scattered radiation from collimation systems was less than 5% of total dose. For the field size, we optimized the tilting angle of the circularly rotating beam controlled by a pair of dipole magnets at the most upstream of the user beam line unit and the thickness of the scatter plate located downstream of the dipole magnets. The values of beam scanning angle and the thickness of the scatter plate could be successfully optimized to be 0.5degrees and 0.05 cm via this Monte Carlo simulation analysis. For the dose uniformity and the beam contamination, we introduced the new beam configuration technique by the combination of scanning and static beams. With the combination of a central static beam and a circularly rotating beam with the tilting angle of 0.5degrees to beam axis, the dose uniformity could be established to be 1.1% in 15x15 cm2 sized maximum field. For the beam contamination, it was determined by the ratio of the absorbed doses delivered by C12 ion and other particles. The level of the beam contamination could be achieved to be less than 2.5% of total dose in the region from 5 cm to 17 cm water equivalent depth in the combined beam configuration. Based on the results, we could establish the optimized nozzle design satisfying the beam conditions which were required for biomedical researches.

Keyword

Accelerator; GEANT4; Heavy ion; Carbon; Nozzle; RAON

MeSH Terms

Axis, Cervical Vertebra
Carbon*
Heavy Ions
Water
Carbon
Water

Figure

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  Fig. 1. The schematic diagram of the experimental beam nozzle for GEANT4 simulation.

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  Fig. 2. The full width half maximums of field versus the thicknesses of scatter plate.

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  Fig. 3. The distances of hone shapes in each lateral profile according to the various tilting angle for beam wobbling.

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  Fig. 4. The normalized lateral dose profiles under conditions with/without the optimized beam tilting angle 0.5o and the diagram of the combined beam delivery: (a) the lateral profile in scatter thickness 0.05 cm and beam tilting angle 0o, (b) the lateral profile in scatter thickness 0.05 cm and beam tilting angle 0.5o, (c) the diagram of the beam combination with a central static beam and a peripheral wobbling beam, and (d) the lateral profile in the combined beam mode for 3500 million MC histories of C12.

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  Fig. 5. The Bragg peaks for C12 beams with energies ranged from 160 to 310 MeV/u.

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  Fig. 6. The C12 ion SOBP beam and the corresponding normalized weighting function for each Bragg peaks with C12 ion energies ranging from 160 to 310 MeV/u.

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  Fig. 7. The percentage of dose delivered by non C12 particles tagged at the water phantom surface was interpreted as the beam contamination level.

Reference

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