Objective: We propose and study a new model aimed at describing the low-dose hyperradiosensitivity phenomenon appearing in the survival curves of different cell lines. Methods: The model uses the induced repair assumption, considering that the critical dose at which this mechanism begins to act varies from cell to cell in a given population. The model proposed is compared with the linear-quadratic model and the modified linear-quadratic model, which is commonly used in literature and in which the induced repair is taken into account in a heuristic way. The survival curve for the MCF-7 line of human breast cancer is measured at low absorbed doses and the uncertainties in these doses are estimated using thermoluminiscent dosemeters. Results: It is shown that these multicellular spheroids present low-dose hyperradiosensitivity. The new model permits an accurate description of the data of two human cell lines (previously published) and of the multicellular spheroids of the MCF-7 line here measured. Conclusion: The model shows enough flexibility to account for data with very different characteristics and considers in a faithful way the hypothesis of the repair induction.

The present study investigated differences in the growth rate of multicellular tumour spheroids of the MCF-7 line of human breast cancer before and after their irradiation. Growth of the spheroids was analysed according to a model based on a Gompertz function. In this model, normalization to a common initial volume is achieved in a way that enables meaningful comparisons to be made between the results obtained for each spheroid. For irradiated spheroids the model includes an additional term to take account of sterilized cells. We found that the growth rate observed before irradiation is not fully recovered by irradiated spheroids and that growth recovery reduces with higher irradiation doses. Surviving fractions obtained at doses below 3 Gy are comparable with those found in clonogenic assays on spheroids of the same cellular line. At larger doses, discrepancies between the different studies are considerable.

A quick and simple method, based on elemental and moisture analyses, is proposed for estimating the mean molecular weight of alkylpolyglucosides and fatty alcohol ethoxylates, which are nonionic surfactants that are attracting growing interest for their ease of biodegradation. Analyses for the water content and the elemental composition were carried out for three alkylpolyglucosides (Henkel-Cognis): Glucopon 215, Glucopon 600, and Glucopon 650, as well as for five fattyalcohol ethoxylates (Kao Corporation): FINDET 10/15, FINDET 10/18, FINDET 1214N/16, FINDET 1214N/23, and FINDET 1618/A18. Application of the method requires knowing the mean number of carbons in the fatty acid chains of the surfactant. This number, in the case of the alkylpolyglucosides assayed here, has been determined experimentally by high-performance liquid chromatography.

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