Bone fragility induced by X-ray irradiation in relation to cortical bone-mineral content.
OBJECTIVE
A large single dose of irradiation to bone tissue causes bone fragility, and such bone will be susceptible to fracture even without trauma. The purpose of this study was to investigate the effects of fractional irradiation on the biomechanical properties of bone in the rat in relation to the cortical bone-mineral content (BMC), and to compare these effects with those brought about by single-dose irradiation.


METHODS
Seventy-five veteran female Wistar rats were divided into 4 groups. Group 1 was the control group. The left tibiae of the remaining rats were exposed to irradiation. Group 2 received one single dose of X-rays at 10-60 Gy. Groups 3 and 4 received fractional irradiation up to different cumulative doses (10-60 Gy): group 3 received 2.5 Gy once a day; group 4 received 1.25 Gy twice a day. Twenty-four weeks after irradiation, the rats were killed and the BMC in each tibial diaphysis was determined by dual-energy X-ray absorptiometry (DXA). The bones were then loaded to failure in a three-point bending test.


RESULTS
The control group showed no difference (p>0.05) between left and right tibiae, neither in BMC nor in the maximum load at fracture. Single-dose irradiation caused a 16% (p=0.0366) decrease in the maximum load at 40 Gy, and a 19% (p=0.008) decrease at 60 Gy. The once-daily fractional dose of irradiation caused a 10% (p=0.0022) decrease in the maximum load of the irradiated tibiae at 60 Gy when compared to the intact contralateral tibiae. The twice-daily fractional dose of irradiation had no observable effect on the maximum load of the irradiated tibiae. Neither fractional irradiation modality had an effect on BMC.


CONCLUSIONS
The study suggested that bone fragility induced by single fractional irradiation doses (given once daily up to high cumulative doses) was not associated with change in the cortical BMC. It also confirmed the preference for twice-daily fractional irradiation as compared to once-daily fractional irradiation and the total single dose.
Nyaruba
M M
MM
Department of Radiology, Shiga University of Medical Science, Japan.
Yamamoto
I
I
Kimura
H
H
Morita
R
R
D015502:Absorptiometry, Photon; D000818:Animals; D015519:Bone Density / Q000528:radiation effects*; D018483:Diaphyses / Q000378:metabolism / Q000503:physiopathology / Q000528:radiation effects; D004195:Disease Models, Animal; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005500:Follow-Up Studies; D005598:Fractures, Spontaneous; D011833:Radiation Injuries, Experimental / Q000378:metabolism* / Q000503:physiopathology; D051381:Rats; D017208:Rats, Wistar; D013718:Tensile Strength / Q000528:radiation effects; D013977:Tibia / Q000378:metabolism / Q000503:physiopathology / Q000528:radiation effects*; D013978:Tibial Fractures / Q000209:etiology* / Q000378:metabolism / Q000503:physiopathology