Proton Microbeam Radiotherapy

 

Researchers

Juergen Meyer, Eunsin Lee, James Eagle, Steve Marsh, Rob Emery, Eric Dorman, Eric Ford

 

Overview

The emerging cancer treatment approach of Microbeam Radiation Therapy (MRT) holds promise to revolutionize the way radiotherapy is performed. The difference from conventional radiotherapy is the ultra-high dose modulation on a micron scale and consequent astonishing radiobiological benefits. Several pre-clinical studies at a few synchrotron facilities have shown effective tumor response to MRT in tumor-inoculated rodent models that are resistant to conventional radiation therapy. Remarkably this is achieved while preserving normal tissue functionality following a nominally lethal high dose from the microbeam irradiation. This “tissue-sparing effect” makes MRT particularly suited for treatment of pediatric brain tumors, causing less damage to the developing central nervous system. The extraordinary normal tissue tolerance to highly spatially modulated high dose MRT beams cannot be explained with our current understanding of the radiobiological processes and requires a paradigm shift in our thinking. The spatial dose modulation, with gradients of hundreds of Gray over tens of microns, is a crucial factor in the efficacy and safe translation of MRT to humans.
Spatially modulated proton beams theoretically offer radiobiological potential that may provide a dosimetric benefit over synchrotron generated kilovoltage X-ray MRT beams, because protons have the distinct dosimetric advantage of depositing a large portion of their energy at depth, referred to as the Bragg peak. By means of Monte Carlo (MC) simulation with TOPAS, we will investigate the feasibility of producing spatially modulated proton beams (pMBRT) on the UW research proton beamline that are comparable in dimensions to synchrotron generated X-ray micro- or minibeams. The ultimate goal of this research is to enable radiobiology research with spatially modulated high dose rate proton beams to be able to conduct comparative measurements with non-modulated beams. Guided by Monte Carlo simulations we will build a collimator with the optimal physical configuration. 



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(a)

(b)

50 MeV proton beamline for small animal research integrated into the Small Animal Radiation Research Platform (SARRP) at the University of Washington, Radiation Oncology Department
Simulated brass collimator with 0.1 mm slit, 1 mm center-to-center spacing and 5 cm thick collimator. (a) 2D depth dose showing the high modulation on the entrance side and uniform dose at depth. The color bars represent relative dose. (b) The cross profiles at 5, 10, 15 mm depth and through the Bragg peak. The high modulation at shallow depth can be clearly seen, whereas at the depth of the tumor the dose is more or less uniform.


Links and Collaboration

Department of Physics and Astronomy, Medical Physics Group, University of Canterbury, Christchurch, NZ


References

Eunsin Lee, Juergen Meyer, Feasibility of spatially modulated proton beams for small animal research, submitted to the 57th Annual Meeting of the American Association of Physicists in Medicine (AAPM), in Anaheim, CA, July 12-16, 2015
 


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