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Dual scattering foil design for poly-energetic electron beams. Phys Med Biol 2005 Mar 07;50(5):755-67

Date

03/31/2005

Pubmed ID

15798252

DOI

10.1088/0031-9155/50/5/002

Scopus ID

2-s2.0-16444384386   6 Citations

Abstract

The laser wakefield acceleration (LWFA) mechanism can accelerate electrons to energies within the 6-20 MeV range desired for therapy application. However, the energy spectrum of LWFA-generated electrons is broad, on the order of tens of MeV. Using existing laser technology, the therapeutic beam might require a significant energy spread to achieve clinically acceptable dose rates. The purpose of this work was to test the assumption that a scattering foil system designed for a mono-energetic beam would be suitable for a poly-energetic beam with a significant energy spread. Dual scattering foil systems were designed for mono-energetic beams using an existing analytical formalism based on Gaussian multiple-Coulomb scattering theory. The design criterion was to create a flat beam that would be suitable for fields up to 25 x 25 cm2 at 100 cm from the primary scattering foil. Radial planar fluence profiles for poly-energetic beams with energy spreads ranging from 0.5 MeV to 6.5 MeV were calculated using two methods: (a) analytically by summing beam profiles for a range of mono-energetic beams through the scattering foil system, and (b) by Monte Carlo using the EGS/BEAM code. The analytic calculations facilitated fine adjustments to the foil design, and the Monte Carlo calculations enabled us to verify the results of the analytic calculation and to determine the phase-space characteristics of the broadened beam. Results showed that the flatness of the scattered beam is fairly insensitive to the width of the input energy spectrum. Also, results showed that dose calculated by the analytical and Monte Carlo methods agreed very well in the central portion of the beam. Outside the useable field area, the differences between the analytical and Monte Carlo results were small but significant, possibly due to the small angle approximation. However, these did not affect the conclusion that a scattering foil system designed for a mono-energetic beam will be suitable for a poly-energetic beam with the same central energy. Further studies of the dosimetric properties of LWFA-generated electron beams will be done using Monte Carlo methods.

Author List

Kainz KK, Antolak JA, Almond PR, Bloch CD, Hogstrom KR

Author

Kristofer Kainz PhD Associate Professor in the Radiation Oncology department at Medical College of Wisconsin




MESH terms used to index this publication - Major topics in bold

Electrons
Equipment Design
Kinetics
Lasers
Models, Statistical
Monte Carlo Method
Normal Distribution
Particle Accelerators
Photons
Radiometry
Radiotherapy Dosage
Radiotherapy, High-Energy
Scattering, Radiation