The effects of dose rate and dose fractionation on high-LET radiation-induced oncogenic transformation of C3H 10T1/2 cells were examined. Cells were irradiated with graded doses of 5.9-MeV monoenergetic neutrons administered either in single acute exposures (30 mGy/min) or extended over an 8-h period at low dose rates (from 0.21 to 1 mGy/min). Although cell survival studies showed no difference in effect with a change in radiation delivery rate, enhancement of oncogenic transformation occurred when the dose rate was reduced. When the neutron dose was divided into three fractions over 8 h, the biological effect was intermediate between that for the acute and that for the low-dose-rate exposures. Further irradiations were made using deuterons with an LET of 40 keV/μm. The dose-mean lineal energy was comparable to that measured for the 5.9-MeV monoenergetic neutrons. An inverse dose-rate/fractionation effect for the induction of transformation by high-LET deuterons was observed when the time between each of three fractions for a 0.3-Gy total dose was at least 45 min. No further enhancement was seen for longer dose fractionations, suggesting that very long protracted exposures of high-LET radiation would produce no additional enhancement.
The Effects of the Temporal Distribution of Dose on Oncogenic Transformation by Neutrons and Charged Particles of Intermediate LET
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Richard C. Miller, David J. Brenner, Gerhard Randers-Pehrson, Stephen A. Marino, Eric J. Hall; The Effects of the Temporal Distribution of Dose on Oncogenic Transformation by Neutrons and Charged Particles of Intermediate LET. Radiat Res 1 October 1990; 124 (1s): S62–S68. doi: https://doi.org/10.2307/3577679
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