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Feasibility of Spatially Modulated Proton Beams for Small Animal Research

E Lee

E Lee*, J Meyer , University of Washington Medical Center, Seattle, WA


WE-EF-BRA-6 (Wednesday, July 15, 2015) 1:45 PM - 3:45 PM Room: Ballroom A

Purpose:To investigate the feasibility of proton minibeam radiotherapy (pMBRT) for small animal research. The motivation is to explore with protons the extraordinary normal tissue sparing effects to spatially modulated beams as observed on high flux synchrotron beam lines. We hypothesized that we can design a multi-slit collimator for our proton beam line to produce planar-parallel dose profiles with high modulation in the entrance region and homogenous dose coverage in the overlap of the Bragg peaks.

Methods:The high dose rate 50 MeV research proton beamline at the University of Washington was modeled using the TOol for PArticle Simulation (TOPAS) Monte Carlo package. A brass collimator was implemented to generate proton minibeams. The collimator consists of an array of 2 cm long slits to cover an area of 2x2 cm2. The slit widths (0.1-1 mm), center-to-center (ctc) distances (1-3 mm) and collimator thickness (1-7 cm) were varied to evaluate the effect on dose rate, the peak-to-valley dose ratios (PVDR) and the change of penumbra and peak width (FWHM) with depth.

Results:The Bragg peak was at a depth of ~21 mm. The penumbra and FWHM remained relatively constant to a depth of about 10-15 mm. The PVDR ranged from 1.6 to 26 and the dose rate dropped exponentially with collimator thickness. A uniform dose can be achieved at depth with slightly compromised PVDRs and dose rate.

Conclusion:The technical realization of pMBRT is feasible. The simulations have shown that it is possible to obtain uniform dose at depth while modulation is maintained on the entrance side. While the simulated beam widths are larger than on synchrotron generated microbeams the dosimetric advantage could avoid having to interlace two microbeams to achieve uniform dose in the target. The next steps are to build a collimator and verify the simulations experimentally.

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