The Effects of Fractionated X-Irradiation on the Growth of Sarcoma 37 in Mice

Abstract

IT has been shown by Warren and Whipple (1923) that small aliquot doses of X-irradiation administered over periods of up to 5 days, produced the same degree of destruction of the intestinal mucosa of dogs as a single total dose. This summation effect was lost if the intervals were spread over a longer period. In the treatment of breast cancer Cohen (1952) has suggested that it is not possible to improve the therapeutic ratio by prolonged daily fractionations. Quimby and MacComb (1937) have shown that if the total dose and total treatment time are constant, the number of fractions is not important. Du Sault (1956) in a review of the effects of fractionated doses in radiation therapy, has postulated a latent period within which any type of fractionation will produce the same effect as a single total dose. The effect of fractionated doses administered after this period-during the period of recovery-depends on the degree of recovery from the preceding dose.Lamarque and Gary-Bobo (1955) have assessed the effects of variations in the time interval between two equal fractions, on the survival of eggs of Bombyx mori. In this work it was shown that a maximum effect was produced by a single total dose, and this effect decreased progressively when the dose was fractionated with time intervals up to 24 hours; an increase was then shown with time intervals of 2 and 4 days. Heeren (1948) has shown that the reticulocyte count in mice is lowered to a greater degree by continuous than by discontinuous irradiation. In studies on erythema Reisner (1932) showed that the effect of a single dose was greater than that of fractionated doses. Schottelndreyer (1949), also studying erythema, showed that the biological effect of a single irradiation of 631 r was equivalent to 2064 r given in 12 daily fractions. Fogg and Cowing (1953) however, report that fractionated doses of 294 r produce a greater effect on spermatogonia and spermatocytes of mice than a single total dose.The present study was undertaken to examine the effects of fractionated X-irradiation at varying time intervals on the growth of a transplantable tumour in mice. MATERIALS AND METHODThe transplantable tumour used in this study was Sarcoma 37, inoculated into RIII strain mice. This tumour was selected for the regularity of its growth rate, and absence of spontaneous regressions when inoculated into this strain. The tumours for each experiment were obtained by inoculating 1 mm.3 portions, from the cortex of an actively growing parent tumour, subcutaneously into the right flank of female mice. Each experiment consisted of control and treated