Low-dose radiation hyper-radiosensitivity in multicellular tumour spheroids.

OBJECTIVE: We propose and study a new model aimed at describing the low-dose hyper-radiosensitivity 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 hyper-radiosensitivity. 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.

A Monte Carlo tool to simulate breast cancer screening programmes.

A Monte Carlo tool which permits the simulation of screening mammography programmes is developed. Various statistical distributions describing different parameters involved in the problem are used: the characteristics of the population under study, a tumour growth model and a model for tumour detection based on parameters such as sensitivity and specificity which depends on the woman's age. We reproduce results of different actual programmes. The model enables us to find out the configuration (the age of the women who attend the screening trials and screening frequency) which produces maximum benefits with minimum risks. In addition, the model has permitted us to validate some of the assumed hypothesis, such as the probability distribution of the tumour detection as a function of the tumour size, the frequency of the histological types and the transition probability between different histological types.