Microdosimetric evaluation of the 400 MeV/nucleon carbon beam at HIMAC.
Microdosimetric single event spectra were determined as a function of depth in an acrylic phantom for the carbon beam at HIMAC using a tissue equivalent proportional counter (TEPC) coupled to a scintillation counter system. The fragments produced by the carbon beam were identified by the deltaE-time of flight distribution obtained from two scintillation counters which were positioned at the up- and down-stream of the TEPC. Lineal energy distribution for the carbon beam and its five fragments, namely, proton, helium, lithium, beryllium, and boron ions, were measured in the lineal-energy range of 5-1000 keV/microm at five phantom depths between 0 and 230 mm. The dose distribution for the carbon beam and its fragments were obtained separately. The relative biological effectiveness (RBE) of the carbon beam in the phantom was calculated using a response function. The maximum RBE for the carbon beam was found to be about 5 near the Bragg peak. It was observed to rapidly decrease for Bragg peaks occurring at deeper positions in the phantom. The dose from the beam fragments accounted for about 30% to the total dose, however, its contribution to the RBE was less than 17%.
Research Institute for Radiation Biology and Medicine, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan. endos@hiroshima-u.ac.jp
Satoru
S
Endo
Kenichi
K
Tanaka
Masayori
M
Ishikawa
Masaharu
M
Hoshi
Yoshihiko
Y
Onizuka
Masashi
M
Takada
Hiroshi
H
Yamaguchi
Naofumi
N
Hayabuchi
Naoko
N
Maeda
Kiyoshi
K
Shizuma
D002244:Carbon; D006801:Humans; D007564:Japan; D018499:Linear Energy Transfer; D010315:Particle Accelerators / Q000706:statistics & numerical data*; D019047:Phantoms, Imaging; D011853:Radiobiology; D011874:Radiometry / Q000706:statistics & numerical data*; D011882:Radiotherapy, High-Energy / Q000706:statistics & numerical data*; D012062:Relative Biological Effectiveness
D002244:Carbon