A simplified two-compartment model for cell-specific chemotherapy is analysed by reformulating the governing system of differential equations as a Schrodinger equation in time. With the choice of an exponentially decaying function representing the effects of chemotherapy on cycling tumor cells, the potential function V(t) is a Morse-type potential, well known in the quantum mechanical literature; and the solutions are obtainable in terms of confluent hypergeometric functions (or the related Whittaker functions). Because the chemotherapy is administered periodically, the potential V(t) is periodic also, and use is made of existing theory (Floquet theory) as applied to scattering by periodic potentials in the quantum theory of solids. Corresponding to the existence \u27\u27forbidden energy bands\u27\u27 in that context, it appears that there are \u27\u27forbidden\u27\u27 or inappropriate chemotherapeutic regimens also, in the sense that for some combinations of period, dosage, and cell parameters, no real solutions exist for the system of equations describing the time evolution of cancer cells in each compartment. A similar, but less complex phenomenon may occur for simpler mathematical representations of the regimen. The purpose of this paper is to identify the existence of this phenomenon, at least insofar as this model is concerned, and to examine the implications for clinical activities. This new paradigm, if structually stable (in the sense of the phenomenon occurring in more realistic models of chemotherapy) may be of considerable significance in identifying those regimens which are appropriate for effective chemotherapy, by providing a rational basis for such decisions, rather than by \u27\u27trial and error\u27\u27 (see the statement by Skipper [1] at the conclusion of this paper)
