The statistics of dose/cure relationships for irradiated tumours. Part II

Everything in this work depends on single-clonogen recurrences: meaning that a tumour is only cured if every clonogen in it is sterilized. This is the simplest and most intuitively appealing theory of tumour recurrence, but there is little direct evidence for it. Indirect evidence can be brought which suggests single-clonogen recurrence for at least some tumours. Porter, Hewitt and Blake (1973) found that at least two experimental murine tumours transplanted “by single cells” (i.e. according to Poisson), and for such tumours single-cell recurrence would be a natural extrapolation. But three other tumours transplanted anomalously, and some reserve would be justified in dealing with them. The anomalous tumours consistently gave relationships between log. inoculum size and take percentage that were flatter than the single-cell curve; so anomalously flat dose/ cure curves might be expected. Malignant tumours, with their abnormal and precarious blood-supply, are liable to infarctions, minor or massive. In a regressing tumour the interstitial pressure will be low, and presumably the infarction risk recedes: thus the critical time should be before and just after irradiation. The effect of an infarction will be to reduce the number of clonogens in the infarcted tumour. If infarctions are small and occur frequently this merely adds some variability to the effective tumour size, and section 3.4 will show that this has little effect.