L. Tallone Lombardi

Relative biological effectiveness for protons of energies up to 31 MeV.

The relative biological effectiveness (RBE) was determined for proton beams of 31, 12, and 8 MeV produced at the Milano University Cyclotron. Survival curves for human cells grown in monolayer at different proton energies and for γ rays from60 Co were determined. The minimum clone size to be chosen for definition of true survivors was examined. RBE values of 1.0 ± 0.1, 1.4 ± 0.2, and 1.5 ± 0.2, respectively, were found and compared with the results of other experiments in this energy range.

Multinucleate Cells and Micronucleus Formation in Cultured Human Cells Exposed to 12 MeV Protons and γ-rays

Cultured human cells of the EUE line were exposed to different doses of 12 MeV protons, plated and allowed to grow for 8 days; colonies were then scored for the presences of multinucleate cells and micronuclei. The frequency of both effects is an increasing function of the dose; the evaluated exponents of the dose-response equation (e = bDn) are n = 1.0 %/- 0.1 for multinucleate cells and n = 1.6 +/- 0.1 for micronuclei. By comparison with the results obtained with gamma irradiations, r.b.e. values were obtained for both effects. The correlation between the logarithm of the surviving fraction and the yield of the studied effects has been proved to be statiscally significant.

Criteria and techniques for analysing cell survival data

SummaryCell survival was studied by analyzing the inactivation probability density function and its fundamental parameters. Mean

Cell density dependence of transformation frequencies in C3H10T1/2 cells exposed to X-rays.

\bar D

Radiocarcinogenesis: Results fromin vitro, experiments

, varianceσ2 and modeDmode were evaluated and a set of equations relating these parameters to the usual parameters of the multitarget, multihit and linear-quadratic modelsDo andn, α andβ, k andλ are reported. The multihit equation used was an extension of the usual equation, to allow parameterk to assume values that are not necessarily integers. In the multitarget curve, the mode of inactivation probability density function, proved to be the quasi-threshold doseDq =Do ln(n). Relative variance, degree of asymmetry and degree of peakedness can be calculated from the shape parametersn in the multitarget model,k in the multihit model, and

Radiocarcinogenesis in vitro: «Inverse dose-rate effect»

\alpha /\sqrt \beta