TY - JOUR
T1 - Relation between lineal energy distribution and relativebiological effectiveness for photon beams accordingto the microdosimetric kinetic model
AU - Okamoto, Hiroyuki
AU - Kanai, Tatsuaki
AU - Kase, Yuki
AU - Matsumoto, Yoshitaka
AU - Furusawa, Yoshiya
AU - Fujita, Yukio
AU - Saitoh, Hidetoshi
AU - Itami, Jun
AU - Kohno, Toshiyuki
PY - 2011
Y1 - 2011
N2 - Our cell survival data showed the obvious dependence of RBE on photon energy: The RBE value for 200 kV X-rays was approximately 10% greater than those for mega-voltage photon beams. In radiation therapy using mega-voltage photon beams, the photon energy distribution outside the field is different with that in the radiation field because of a large number of low energy scattering photons. Hence, the RBE values outside the field become greater. To evaluate the increase in RBE, the method of deriving the RBE using the Microdosimetric Kinetic model (MK model) was proposed in this study. The MK model has two kinds of the parameters, tissue-specific parameters and the dose-mean lineal energy derived from the lineal energy distributions measured with a Tissue-Equivalent Proportional Counter (TEPC). The lineal energy distributions with the same geometries of the cell irradiations for 200 kV X-rays, 60Co γ-rays, and 6 MV X-rays were obtained with the TEPC and Monte Carlo code GEANT4. The measured lineal energy distribution for 200 kV X-rays was quite different from those for mega-voltage photon beams. The dose-mean lineal energy of 200 kV X-rays showed the greatest value, 4.51 keV/μm, comparing with 2.34 and 2.36 keV/μm for 60Co γ-rays and 6 MV X-rays, respectively. By using the results of the TEPC and cell irradiations, the tissue-specific parameters in the MK model were determined. As a result, the RBE of the photon beams (yD: 2~5 keV/μm) in arbitrary conditions can be derived by the measurements only or the calculations only of the dose-mean lineal energy.
AB - Our cell survival data showed the obvious dependence of RBE on photon energy: The RBE value for 200 kV X-rays was approximately 10% greater than those for mega-voltage photon beams. In radiation therapy using mega-voltage photon beams, the photon energy distribution outside the field is different with that in the radiation field because of a large number of low energy scattering photons. Hence, the RBE values outside the field become greater. To evaluate the increase in RBE, the method of deriving the RBE using the Microdosimetric Kinetic model (MK model) was proposed in this study. The MK model has two kinds of the parameters, tissue-specific parameters and the dose-mean lineal energy derived from the lineal energy distributions measured with a Tissue-Equivalent Proportional Counter (TEPC). The lineal energy distributions with the same geometries of the cell irradiations for 200 kV X-rays, 60Co γ-rays, and 6 MV X-rays were obtained with the TEPC and Monte Carlo code GEANT4. The measured lineal energy distribution for 200 kV X-rays was quite different from those for mega-voltage photon beams. The dose-mean lineal energy of 200 kV X-rays showed the greatest value, 4.51 keV/μm, comparing with 2.34 and 2.36 keV/μm for 60Co γ-rays and 6 MV X-rays, respectively. By using the results of the TEPC and cell irradiations, the tissue-specific parameters in the MK model were determined. As a result, the RBE of the photon beams (yD: 2~5 keV/μm) in arbitrary conditions can be derived by the measurements only or the calculations only of the dose-mean lineal energy.
KW - Microdosimetry
KW - Monte Carlo simulation
KW - Photon
KW - Proportional counter
KW - RBE
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U2 - 10.1269/jrr.10073
DO - 10.1269/jrr.10073
M3 - Article
C2 - 21160135
AN - SCOPUS:79751502084
VL - 52
SP - 75
EP - 81
JO - Journal of Radiation Research
JF - Journal of Radiation Research
SN - 0449-3060
IS - 1
ER -