This article focuses on the analytic modeling of responses of cells in the body
to ionizing radiation. The related mechanisms are consecutively taken into
account and discussed. A model of the dose- and time-dependent adaptive response
is considered for 2 exposure categories: acute and protracted. In case of the
latter exposure, we demonstrate that the response plateaus are expected under
the modelling assumptions made. The expected total number of cancer cells as a
function of time turns out to be perfectly described by the Gompertz function.
The transition from a collection of cancer cells into a tumor is discussed at
length. Special emphasis is put on the fact that characterizing the growth of a
tumor (ie, the increasing mass and volume), the use of differential equations
cannot properly capture the key dynamics—formation of the tumor must exhibit
properties of the phase transition, including self-organization and even
self-organized criticality. As an example, a manageable percolation-type phase
transition approach is used to address this problem. Nevertheless, general
theory of tumor emergence is difficult to work out mathematically because
experimental observations are limited to the relatively large tumors. Hence,
determination of the conditions around the critical point is uncertain.