Correction factors to convert microdosimetry measurements in silicon to tissue in 12C ion therapy

Silicon microdosimetry is a promising technology for heavy ion therapy (HIT)
quality assurance, because of its sub-mm spatial resolution and capability to
determine radiation effects at a cellular level in a mixed radiation field. A
drawback of silicon is not being tissue-equivalent, thus the need to convert the
detector response obtained in silicon to tissue. This paper presents a method
for converting silicon microdosimetric spectra to tissue for a therapeutic 12C
beam, based on Monte Carlo simulations. The energy deposition spectra in
a 10 μm sized silicon cylindrical sensitive volume (SV) were found to be
equivalent to those measured in a tissue SV, with the same shape, but with
dimensions scaled by a factor κ equal to 0.57 and 0.54 for muscle and water,
respectively. A low energy correction factor was determined to account for
the enhanced response in silicon at low energy depositions, produced by
electrons. The concept of the mean path length lPath to calculate the lineal
energy was introduced as an alternative to the mean chord length l because
it was found that adopting Cauchy’s formula for the l was not appropriate
for the radiation field typical of HIT as it is very directional. lPath can be
determined based on the peak of the lineal energy distribution produced by
the incident carbon beam. Furthermore it was demonstrated that the thickness
of the SV along the direction of the incident 12C ion beam can be adopted
as lPath . The tissue equivalence conversion method and lPath were adopted
to determine the RBE10, calculated using a modified microdosimetric kinetic
model, applied to the microdosimetric spectra resulting from the simulation
study. Comparison of the RBE10 along the Bragg peak to experimental TEPC measurements at HIMAC, NIRS, showed good agreement. Such agreement demonstrates the validity of the developed tissue equivalence correction
factors and of the determination of lPath .

書誌情報

Physics in Medicine and Biology

巻 62, 号 6, p. 2055-2069, 発行日 2017-03

出版者

IOP Publishing

ISSN

収録物識別子タイプ

ISSN

収録物識別子

1120-1797

DOI

識別子タイプ

DOI

Versions

Ver.1

2023-05-15 23:31:07.400843

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