Lethal effect of carbon K-shell photoionizations in Chinese hamster V79 cell nuclei: experimental method and theoretical analysis.
To test a possible specific effect of carbon K-shell ionizations in DNA, survival curves for Chinese hamster V79 cells were measured for X irradiations at energies below and above the carbon K-shell ionization threshold. Specific values of the X-ray energies (250 and 340 eV) were chosen to ensure isoattenuation of the two kinds of radiation within the cell. An enhancement of lethality by a factor of about 2 was found for X rays at 340 eV compared to below the threshold at 250 eV. This may be attributed to the production of highly efficient carbon K-shell ionizations located on DNA. A model of X-ray lethality (Goodhead et al., Radiat. Prot. Dosim. 52, 217-223, 1994) was extended to allow for a possible lethal effect from clusters of reactive species induced by K-shell photoionizations (K-shell clusters). Within this model, the increase in lethality above the carbon K-shell threshold may be explained by a value of 2% for the lethal efficiency of K-shell clusters overlapping the DNA. An extrapolation to the lethal effect of more complex ion-induced K-shell ionizations indicates that K-shell ionization may be a major process in the biological effectiveness of heavy ions.
Herve du Penhoat
M A
MA
Groupe de Physique des Solides, Universités Paris 7 et Paris 6 (CNRS UMR 75-88, CEA LRC No.6), France.
Fayard
B
B
Abel
F
F
Touati
A
A
Gobert
F
F
Despiney-Bailly
I
I
Ricoul
M
M
Sabatier
L
L
Stevens
D L
DL
Hill
M A
MA
Goodhead
D T
DT
Chetioui
A
A
D000818:Animals; D002244:Carbon; D002460:Cell Line; D002467:Cell Nucleus / Q000528:radiation effects*; D002470:Cell Survival / Q000528:radiation effects; D006224:Cricetinae; D003412:Cricetulus; D004247:DNA / Q000528:radiation effects*; D020450:Heavy Ions; D012062:Relative Biological Effectiveness; D014965:X-Rays
D002244:Carbon; D004247:DNA