title: Effects of single-pulse (< or = 1 ps) X-rays from laser-produced plasmas on mammalian cells.
abstract: The effects of low linear energy transfer (LET) radiation on mammalian cells have been studied at dose-rates as high as 10(9) Gy/sec delivered as a single 3-nanosecond pulse, and no increase in cytotoxicity was shown compared with delivery at a conventional dose-rate. There have been no observations on the effects of radiation delivered at even higher dose-rates on the picosecond time-scale. Here we examined, for the first time, the effects on cultured mouse L5178Y cells and its radiosensitive XRCC4-deficient mutant M10 cells of sub-picosecond X-rays emitted from laser-produced plasmas at the ultrahigh dose-rate of 10(12)-10(13) Gy/sec. No increase in the sensitivity to the X-rays was observed compared with gamma-rays at a conventional dose-rate. The increase in the sensitivity of L5178Y cells by labeling with 5-iododeoxyuridine was smaller than those irradiated with gamma-rays at a conventional dose-rate, while the difference was apparently the reverse in M10 cells. The D10 ratio between L5178Y cells and M10 cells produced by the X-rays at temporally dense ionization was the same as that produced by X(gamma)-rays at the conventional dose-rate, while the ratio is greatly reduced in the case of particle radiation. These results suggest that there is no increase in the cytotoxic effects of X-rays at dose-rates as high as 10(13) Gy/sec, and that the increased cytotoxicity of particle radiation is not attributable to temporally dense ionization. It is discussed that the mechanism for the induction of radiation damage responsible for cytotoxicity may be slightly modified at ultrahigh dose-rates.
authors.affiliation: Radiation Research Institute, Graduate School of Medicine, The University of Tokyo, Japan.
authors.forename: Kunio
authors.initials: K
authors.lastname: Shinohara
authors.forename: Hisako
authors.initials: H
authors.lastname: Nakano
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Miyazaki
authors.forename: Masao
authors.initials: M
authors.lastname: Tago
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Kodama
mesh_terms: D000818:Animals; D002460:Cell Line / Q000528:radiation effects*; D002586:Cesium; D004247:DNA / Q000528:radiation effects*; D004249:DNA Damage; D004260:DNA Repair; D004307:Dose-Response Relationship, Radiation; D005720:Gamma Rays; D007065:Idoxuridine / Q000494:pharmacology; D007477:Ions; D007834:Lasers; D018499:Linear Energy Transfer; D051379:Mice; D013997:Time Factors; D014965:X-Rays
chemical_list: D007477:Ions; D002586:Cesium; D004247:DNA; D007065:Idoxuridine