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R J Yaes

Publications and source records attributed to R J Yaes.

44 records · Page 3Linked to original sources
PubMed1988

Some implications of the Linear Quadratic model for tumor control probability.

To define an optimal radiation therapy strategy, the dependence of the probability of cure and of significant complications, on the parameters controlled by the radiotherapist must be determined. The recent success of the Linear Quadratic (LQ) model in constructing isoeffect relations for normal tissue damage and in describing in vitro cell survival curves, indicate that this model could be used to determine this dependence. The problem of tumor control is addressed. Using LQ model parameters obtained from human tumor cell lines, the sigmoid dose-response curves for controlling tumors of fixed size but of several histologies, with a fractionated course of radiotherapy is obtained. Except for squamous cell carcinoma, the calculated average tumor control doses (TCD37 or TCD50) are unrealistically low, but the model can be made more realistic by including inhomogeneities in the spatial dose distribution and heterogeneous tumor cell populations. The slope of the dose response curves are determined and the significance of the "relative slope" parameter rho as a measure of the number of cells in a tumor's most radioresistant clone is noted. The relation of the model's predictions to qualitative features of the experimental animal data for both tumor control and for normal tissue damage is discussed. Experiments to test the validity of this type of model are suggested.

Cell Line↗
PubMed1988

Local stem cell depletion model for radiation myelitis.

We propose a model for normal tissue damage based on the assumption that adult mammalian stem cells have limited mobility and, consequently, for each organ, there is a maximum volume (the "critical volume," Vc), that can be repopulated and repaired by a single surviving stem cell. This concept is applied to a simple, 1-dimensional model of the spinal cord, where the critical volume is a "slice" of "thickness," t, assumed to be small compared to lengths of spinal cord usually irradiated clinically. The probability of myelitis is explicitly obtained as a function of the dose, dose per fraction, length of cord irradiated, slice thickness, number of stem cells per slice and parameters alpha and beta of the stem cell survival curve. The complication probability is expressed as a triple negative exponential function of dose analogous to the double negative exponential function for tumor control, resulting in a steep dose-response curve with short tails in both the high dose and low dose regions. We show that the model predictions are compatible with the experimental data for radiation myelitis in the rat. We discuss how this concept can be applied to other organs such as skin and to organs composed of structurally and functionally distinct subunits, such as the kidney.

Animals↗