Late radiation damage to the rat femur and the NSD formula

The extraction of 86Rb chloride, the red blood cell volume and the mineral content in the rat femur have been studied 7 months after local X-irradiation. Doses were given as 3, 6 and 9 fractions over three weeks. The total doses used were based on NSD value of 1450 and 1900 on the basis of the results from our previous single dose irradiation studies. The reduction in the extraction of 86Rb chloride was statistically significant for all fractionation schemes and at both NSD levels. In the whole femur, with bone marrow, the extraction was reduced by 33% to 46%. In the hard bone the reduction was less only 18% to 38%. There was no significant difference between the fractionation schemes used at each NSD level. The red blood cell volume was significantly reduced in the whole femur, with bone marrow, with no difference between the fractionation schemes. However, there was no change in the hard bone. The dry bone weight was reduced by 3 to 6% with no significant difference between the different fractionation schemes. The dose levels predicted by the NSD formula produced approximately the same damage to the rat femur 7 months after the irradiation when the dry weight and the extraction of 86Rb chloride were used as end points for the evaluation of the severity of late radiation damage.