Optimum fractionation in X-ray treatment of C3H mouse mammary tumours

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Abstract
The doses required to control 50 per cent of tumours at 150 days after irradiation were determined for eight fractionated X-ray schedules. The tumours were first-generation transplants from spontaneous mammary tumours in C3H/ He mice. The schedules were: single doses, 5, 9 or 15 fractions given daily excluding weekends, and 2, 3, 5 or 9 fractions at the two-day interval known to be optimal for reoxygenation in these tumours after a priming dose of 1,500 rads. For comparison, skin reactions on the feet of albino mice were determined, using the same fractionation schedules, in order to plot the tumour control probability (TCP) against skin reactions for corresponding schedules. Two optimum schedules were found which gave maximum local control of tumours for the lowest skin reaction: nine fractions in ten days (9F/10d) and 5F/9d. The treatments given in shorter overall times were fairly good if the two-day intervals were used but were poor for “daily” doses. Both schedules employing overall times of 18 days gave poor results. The results are discussed in relation to the time course of reoxygenation and cell proliferation. A substantial difference in TCD 50 was found between male and female mice, the females being easier to cure.