Contribution of indirect action to radiation-induced mammalian cell inactivation: dependence on photon energy and heavy-ion LET.
The contribution of indirect action mediated by OH radicals to cell inactivation by ionizing radiations was evaluated for photons over the energy range from 12.4 keV to 1.25 MeV and for heavy ions over the linear energy transfer (LET) range from 20 keV/microm to 440 keV/microm by applying competition kinetics analysis using the OH radical scavenger DMSO. The maximum level of protection provided by DMSO (the protectable fraction) decreased with decreasing photon energy down to 63% at 12.4 keV. For heavy ions, a protectable fraction of 65% was found for an LET of around 200 keV/microm; above that LET, the value stayed the same. The reaction rate of OH radicals with intracellular molecules responsible for cell inactivation was nearly constant for photon inactivation, while for the heavy ions, the rate increased with increasing LET, suggesting a reaction with the densely produced OH radicals by high-LET ions. Using the protectable fraction, the cell killing was separated into two components, one due to indirect action and the other due to direct action. The inactivation efficiency for indirect action was greater than that for direct action over the photon energy range and the ion LET range tested. A significant contribution of direct action was also found for the increased RBE in the low photon energy region.
Ito
Atsushi
A
Course of Energy Engineering, Department of Applied Science, School of Engineering, Tokai University, Hiratsuka-shi, Kanagawa 259-1292, Japan. aeito@keyaki.cc.u-tokai.ac.jp
Nakano
Hisako
H
Kusano
Yohsuke
Y
Hirayama
Ryoichi
R
Furusawa
Yoshiya
Y
Murayama
Chieko
C
Mori
Tomoyuki
T
Katsumura
Yosuke
Y
Shinohara
Kunio
K
D002470:Cell Survival / Q000187:drug effects* / Q000528:radiation effects*; D003198:Computer Simulation; D004121:Dimethyl Sulfoxide / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D018922:HL-60 Cells; D020450:Heavy Ions; D006801:Humans; D006878:Hydroxides / Q000378:metabolism; D018499:Linear Energy Transfer; D008954:Models, Biological; D017785:Photons; D011829:Radiation Dosage; D011837:Radiation-Protective Agents / Q000008:administration & dosage
D006878:Hydroxides; D011837:Radiation-Protective Agents; C031356:hydroxide ion; D004121:Dimethyl Sulfoxide