The influence of intracellular recovery and hypoxic cells on the radiation response of mammary tumours and skin in C3H mice.

Abstract

Spontaneous and transplanted tumours in the C3H mouse have been irradiated in oxygen at one atmosphere absolute using either single doses or doses split into two equal fractions with the time interval between them being varied from one hour to three days. The response of the tumours was compared with that of the skin over and around the tumour as representing normal tissue. Intracellular recovery for both tumour types, shown by a positive (D2–D1) 6 hours was seen at all doses studied, and evidence was given for recovery in the hypoxic proportion of the tumour. The skin showed a gradual decrease in (D2–D1) 6 hours as the dose increased, until after an initial dose of 2,750 rads no intracellular recovery was seen with a negative (D2–D1) at all intervals up to three days. This and the sensitisation in the tumours seen at longer time intervals (i.e. negative (D2–D1)) are interpreted as reoxygenation phenomena, or change in proportion of hypoxic cells. The rate and amount of reoxygenation were observed to be greater in spontaneous than in transplanted tumours. The therapeutic advantages of short time intervals are discussed.