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Three-Dimensional Energy Fluence Estimates for Future Treatment Planning Systems

U Titt

U Titt*, D Mirkovic, R Mohan, UT MD Anderson Cancer Center, Houston, TX

SU-C-500-4 Sunday 1:00PM - 1:55PM Room: 500 Ballroom

Purpose: Innovative proton treatment planning necessitates taking variations in the relative biological effectiveness (RBE) of the particles into account. To calculate variable RBE, knowledge of the dose averaged linear energy transfer (LET-d) is of essence. Furthermore, LET-d is dependent on the energy fluence spectrum at the location of interest. This study was designed to provide three dimensional energy fluence spectra for the scanned proton beams at the Proton Therapy Center used by the M. D. Anderson Cancer Center.

Methods:A water phantom containing 21,000 cells, arranged concentric around the beam axis, was designed and implemented in the Monte Carlo code MCNPX. Each cell scores the fluence spectrum of protons as a function of radius from central axis and as a function of depth. The energy spectrum is scored in 1 MeV resolution from 0 to 230 MeV, the spatial resolution in the phantom is 1 mm in radius and 1 mm in depth. Each simulation provides a total number of 4.83e6 values for the analysis.

Results:All clinically used scanned proton beams have been simulated and the 3-dimensional energy fluence in water has been scored. From this data the determination of 3-d doses, as well as 3-d LET-d spectra is straight forward by application of stopping power values, which are provided by the Monte Carlo simulation code. Current efforts focus on the development of a method to scale energy fluence in water to energy fluence in arbitrary materials by use of stopping power ratios.

Conclusion:A complete library of 3-dimensional energy fluence values for protons in water has been computed. Further efforts are made to estimate the energy fluence in arbitrary media in patients.

Funding Support, Disclosures, and Conflict of Interest: NCI grant P01CA021239

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