gms | German Medical Science

48th Meeting of the Particle Therapy Co-Operative Group

Particle Therapy Co-Operative Group (PTCOG)

28.09. - 03.10.2009, Heidelberg

GafChromic film spectroscopy of a laser-accelerated proton beam: a dose to water, Monte Carlo approach

Meeting Abstract

  • D. Kirby - University of Birmingham, Birmingham, United Kingdom
  • S. Green - Dept of Medical Physics, University Hospital Birmingham, Birmingham, United Kingdom
  • F. Fiorini - University of Birmingham, Birmingham, United Kingdom
  • L. Romagnani - Centre for Plasma Physics, Queen's University Belfast, Belfast, United Kingdom
  • M. Borghesi - Centre for Plasma Physics, Queen's University Belfast, Belfast, United Kingdom
  • S. Kar - Centre for Plasma Physics, Queen's University Belfast, Belfast, United Kingdom
  • D. Doria - Centre for Plasma Physics, Queen's University Belfast, Belfast, United Kingdom

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog112

DOI: 10.3205/09ptcog112, URN: urn:nbn:de:0183-09ptcog1127

Published: September 24, 2009

© 2009 Kirby et al.
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Outline

Text

Ion beam therapy (IBT) is a steadily growing field of radiotherapy, with now around 30 centres worldwide offering therapy with mainly proton and/or carbon ion beams. One of the current drawbacks with IBT is the cost of the accelerator required to produce fast ions, and alternative means of ion acceleration are being sought which could rival the beam characteristics of modern cyclotrons and synchrotrons. One highly active area of research is acceleration in plasmas created by intense, short pulsed, high-powered lasers [1].

The TARANIS laser at Queens University Belfast was used to accelerate protons from a 10 μm Au foil target via target normal sheath acceleration (TNSA) [2]. A stack of dose-to-water calibrated GafChromic films consisting of HD810 and EBT was placed 2.5 cm from the target to measure dose-to-water versus depth. Currently the TARANIS setup is capable of accelerating protons up to approximately 12 MeV.

The Monte Carlo code FLUKA was used to produce an array of Bragg curves in water for initial proton energies between 0-15 MeV, combined with a previously determined GafChromic film proton response function [3]. These Bragg curves were iteratively summed with different weightings until they agreed with proton depth-dose measurements, resulting in a histogram-like measurement of proton energy spectrum. To account for the energy loss due to a 20 μm Al filter in front of the film stack, FLUKA was used to create a matrix containing the energy loss transformations for each individual energy bin. Multiplication by the pseudo-inverse of this matrix results in "up-shifting" protons to higher energies. A simple thermal expansion model which describes energy spectra resulting from TNSA was fitted, giving a proton temperature (kBT) of 3.97 MeV and total number of protons (N0) of 5.76·1013 cm-2 which is comparable to GafChromic film measurements made elsewhere using similar laser accelerator apparatus. This work demonstrates the successful application of the dose-to-water formalism in dosimetry of laser accelerated ion beams, and also leads to a more accurate estimate of the proton spectrum and total proton yield than has been previously obtained.

This work was supported by EPSRC (grant number EP/E035728/1) and the LIBRA consortium.


References

1.
Borghesi M, et al. Multi-MeV proton source investigations in ultraintense laser-foil interactions. Phys Rev Let 2004;92:055003.
2.
Hatchett SP, et al. Electron, photon, and ion beams from the relativistic interaction of Petawatt laser pulses with solid targets. Plasma Phys. 2004;7:2076.
3.
Kirby D, et al. LET dependence of GafChromic films and an ion chamber in low enegy proton dosimetry [submitted]. Phys Med Biol. 2009.