Repair kinetics as a determining factor for late tolerance of central nervous system to low dose rate irradiation.
The effect of continuous irradiation, delivered at four different dose rates (107.6, 14.7, 3.9 and 2 Gy.h-1) has been investigated using the rat cervical spinal cord biological system. The endpoint was the induction of foreleg paralysis at 9 months which corresponds, as has been described before, to white matter necrosis. Paralysis occurring in 50% of the animals was taken as the isoeffect, and the ED50 (radiation dose leading to paralysis in 50% of the animals) was calculated by probit analysis. There was a constant increase in the ED50 with the decrease in the dose rate, resulting from the repair of sublethal damage (SLD) occurring during irradiation. A comparison was made with the previously published results of high dose rate (100-120 Gy.h-1) fractionated irradiations (2, 4 and 10 fractions). alpha/beta (1.6 Gy for the pooled fractionation and dose rate data) and the half-time of SLD repair (82 min) were derived.
Scalliet
P
P
Laboratory of Experimental Radiotherapy, AZ St Rafaël, Leuven, Belgium.
Landuyt
W
W
van der Schueren
E
E
D000818:Animals; D002490:Central Nervous System / Q000528:radiation effects*; D004260:DNA Repair / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D008297:Male; D011829:Radiation Dosage; D011833:Radiation Injuries, Experimental / Q000503:physiopathology*; D011836:Radiation Tolerance; D051381:Rats; D013997:Time Factors