  Using 31P-NMR spectroscopy the chronological behavior of the ATP-metabolism
of the tumor spheroids C3H-MA, 9L-Gliome and the mono-layer L1210 has been
analyzed via decrease of the {\beta}-peak. All three cell lines show
characteristic periods, and a homeostatic control cannot be recognized.
Essential components of these periods are circadian (i.e. one day),
circa-semiseptan (i.e. 3.5 days) and circa-septan (i.e. one week). The
determination of the survival fractions provides an optimum exploitation of
radiation damages, when the ATP-concentration assumes a maximum value. This
optimum is reached, when all three cycles exhibit the ATP maximum, which is
only possible by accounting for the circa-septan rhythm. The goal of this study
is to elaborate an optimal fractionation scheme with regard to the irradiation
of tumors.
