Abstract
Hyperthermia (10 min at 45/sup 0/C) immediately prior to graded radiation doses (hX) reduced the D/sub 0/ by a factor of 1.4 from that of the radiation-only survival curve (X). However, fractionated treatment consisting of 10 min at 45/sup 0/C + 4 Gy (hx) followed at various times by hX (hx + time + hX) resulted in a D/sub 0/ which increased with longer fractionation intervals and for an interval of 24 h was 1.4 times that of the control heat-radiation survival curve (hX) and thus became similar to the D/sub 0/ of the control radiation survival curve (X). Furthermore, a radiation survival curve 24 h after 10 min at 45/sup 0/C + 4 Gy (hx + 24 + X) showed a D/sub 0/ which was larger than that of the control radiation survival curve (X), but the increase was less (factor of 1.2) than that for the fractionation of hx + 24 + hX relative to hX. The fractionation of radiation alone (x + 24 + X), or a pretreatment by heat alone (h + 24 + X) did not increase significantly the D/sub 0/ of the radiation survival curve over that of the control (X). However, a pretreatmentmore » by radiation alone, 24 h before combined heat and radiation (x + 24 + hX), increased the D/sub 0/ also by a factor of 1.4 compared to that of the hX control. However, in contrast to the control radiation survival curve (X) and the fractionation survival curve hx + 24 + hX, the fractionation survival curve x + 24 + hX had no shoulder (n = 1). These results indicate that cell killing by combined heat and radiation in fractionated protocols cannot be predicted from the inactivation kinetics of combined heat and radiation based on single treatments when the fractionation interval is more than one cell-cycle time.« less
Published Version
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