The effects of the temporal distribution of dose on oncogenic transformation by neutrons and charged particles of intermediate LET.
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/microns. 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.
Miller
R C
RC
Center for Radiological Research, College of Physicians and Surgeons of Columbia University, New York, New York 10032.
Brenner
D J
DJ
Randers-Pehrson
G
G
Marino
S A
SA
Hall
E J
EJ
D000818:Animals; D002460:Cell Line; D002470:Cell Survival / Q000528:radiation effects; D002471:Cell Transformation, Neoplastic / Q000528:radiation effects*; D003903:Deuterium; D004307:Dose-Response Relationship, Radiation; D004735:Energy Transfer; D051379:Mice; D008809:Mice, Inbred C3H; D009502:Neutrons; D011829:Radiation Dosage; D013997:Time Factors
D003903:Deuterium