| Abstrakt: |
Dose : cure-rate curves for single exposures have been calculated for model tumours containing various numbers of anoxic cells, and for various values of the oxygen : nitrogen sensitivity ratio m. There is a “threshold” number of anoxic cells. Numbers much smaller than this have no effect on the dose needed to cure the tumour; with larger numbers all the well oxygenated cells are killed by doses that leave significant numbers of anoxic cells alive. The value of the “threshold” number depends sharply on m. If the model can be applied qualitatively to the more complex problem of a human tumour, it suggests that when the balance between the success and failure of treatment determined by the radioresistance of anoxic cells, decreasing m, e.g.by employing radium at a low dose-rate rather than fractionated X radiation at a high dose-rate, should produce appreciably better cure-rates. The clinical data available at present do not support this prediction; possible reasons for the apparent anomaly are suggested. |
