Commentary and Review Series 2-98
F values as cytogenetic fingerprints of prior exposure to different radiation qualities: Prediction, reality and future
Nakamura N, Tucker JD, Bauchinger M, Littlefield LG, Lloyd DC, Preston RJ, Sasaki MS, Awa AA, Wolff SRadiat Res 150:492-4, 1998
Summary
Based on theoretical considerations, Brenner and Sachs hypothesized that, when compared to X or gamma rays, densely-ionizing radiations would produce a smaller ratio of interchromosomal (dicentrics or translocations) to intrachromosomal (centric rings or pericentric inversions) chromosome aberrations (termed F value). Published information seemed to favor the hypothesis, with then-available data suggesting that the F value might be greater than 10 for radiations with low linear energy transfer (LET), such as X and gamma rays, and significantly less than 10 for high-LET radiations, such as neutrons or alpha particles. Further, as the F value observed in lymphocytes from A-bomb survivors was reported to be around 6, Brenner suggested that the majority of A-bomb radiation was neutrons. On the other hand, Bauchinger and his colleague reported that the F-value hypothesis was not supported from their own cytogenetic data of various radiations with different LET.
A one-day workshop was held at the Radiation Effects Research Foundation, Hiroshima, on 24 February 1998 to exchange current knowledge and data. Participating were cytogeneticists from around the world and Dr. Brenner.
Summary of individual reports showed that despite large interlaboratory variability in F values results from all the laboratories did not indicate dose or LET dependence of the F values at doses above 1 Gy, in agreement with theoretical considerations. Below 1 Gy, both results to support and not to support the hypothesis exist. Because unexpectedly large interlaboratory variability in the F values was noted, wrong conclusions can be derived if results from different laboratories are compared. In vitro data from RERF showed F values of 5.7 and 6.5 (neutrons), 6.9 (X rays), and 6.1 (gamma rays), which did not differ from survivor data (F values of 6.7 and 7.1). Consequently, the hypothesis that the majority of A-bomb radiation is derived from neutrons is not supported.
Several problems are noted in applying F values to determine retrospective exposure to high-LET radiations. Namely, when neither dose nor radiation quality is known, it is difficult to identify which samples were exposed to doses below 1 Gy. Further, since the aberration frequency is low, a large number of cells need to be scored, which raises a problem of insufficient numbers of cells available for examination. In all, it is not practical to use the F value as a cytogenetic fingerprint of exposure to radiations of different quality. An alternative indicator, termed the H value (ratio of interchromosomal to intrachromosomal intra-arm aberrations) seems to be a promising parameter, and Bauchinger presented some confirming experimental data. Before it can be used retrospectively for in vivo human exposures, however, it will be necessary to develop efficient methods to detect interstitial deletions to apply the H value many years after exposure in individuals such as A-bomb survivors.
Based on theoretical considerations, Brenner and Sachs hypothesized that, when compared to X or gamma rays, densely-ionizing radiations would produce a smaller ratio of interchromosomal (dicentrics or translocations) to intrachromosomal (centric rings or pericentric inversions) chromosome aberrations (termed F value). Published information seemed to favor the hypothesis, with then-available data suggesting that the F value might be greater than 10 for radiations with low linear energy transfer (LET), such as X and gamma rays, and significantly less than 10 for high-LET radiations, such as neutrons or alpha particles. Further, as the F value observed in lymphocytes from A-bomb survivors was reported to be around 6, Brenner suggested that the majority of A-bomb radiation was neutrons. On the other hand, Bauchinger and his colleague reported that the F-value hypothesis was not supported from their own cytogenetic data of various radiations with different LET.
A one-day workshop was held at the Radiation Effects Research Foundation, Hiroshima, on 24 February 1998 to exchange current knowledge and data. Participating were cytogeneticists from around the world and Dr. Brenner.
Summary of individual reports showed that despite large interlaboratory variability in F values results from all the laboratories did not indicate dose or LET dependence of the F values at doses above 1 Gy, in agreement with theoretical considerations. Below 1 Gy, both results to support and not to support the hypothesis exist. Because unexpectedly large interlaboratory variability in the F values was noted, wrong conclusions can be derived if results from different laboratories are compared. In vitro data from RERF showed F values of 5.7 and 6.5 (neutrons), 6.9 (X rays), and 6.1 (gamma rays), which did not differ from survivor data (F values of 6.7 and 7.1). Consequently, the hypothesis that the majority of A-bomb radiation is derived from neutrons is not supported.
Several problems are noted in applying F values to determine retrospective exposure to high-LET radiations. Namely, when neither dose nor radiation quality is known, it is difficult to identify which samples were exposed to doses below 1 Gy. Further, since the aberration frequency is low, a large number of cells need to be scored, which raises a problem of insufficient numbers of cells available for examination. In all, it is not practical to use the F value as a cytogenetic fingerprint of exposure to radiations of different quality. An alternative indicator, termed the H value (ratio of interchromosomal to intrachromosomal intra-arm aberrations) seems to be a promising parameter, and Bauchinger presented some confirming experimental data. Before it can be used retrospectively for in vivo human exposures, however, it will be necessary to develop efficient methods to detect interstitial deletions to apply the H value many years after exposure in individuals such as A-bomb survivors.