Role of vitamin D3 in prevention of radiotherapy-induced epiphyseal injury

Vitamin D3 is a growth factor improving bone mineralization, and regulating osteoblastic activity and longitudinal bone growth. In this study, impact of vitamin D3 supplementation administered prior to fractionated RT in reducing RT-induced epiphyseal injury is investigated. Six week old male Sprague-Dawley rats were enrolled to one of the four groups: Group 1 was assigned as control group (n=7); Group 2 received fractionated RT alone; Group 3 received 50000 IU/kg i.m. vitamin D3 injection alone; and Group 4 received 50000 IU/kg i.m. vitamin D3 injection prior to fractionated RT. Fractionated RT in the irradiated groups was delivered to distal femur and proximal tibia in the left legs of each rats to a total dose of 24 Gy in 3 fractions with the contralateral right leg as the non irradiated control. Vitamin D3 injection in Group 3 was performed on the day before the RT. Bone growth was calculated according to the lengths of femur, tibia and total leg measured on the radiographs taken at the time and 6 weeks after the delivery of RT. RT resulted in a mean percent overall limb growth loss of 56.2% ± 6.7% and a mean percent overall limb discrepancy of 12.7% ± 1.3%. Administration of 50000 IU/kg i.m. vitamin D3 before RT reduced the mean percent overall limb growth loss and the mean percent overall limb discrepancy to 28.5% ± 5.6% and 4.4% ± 3.3%, respectively. These values were significantly different compared with the groups receiving irradiation alone (P=0.001 for each). In conclusion, these result demonstrated the potential for vitamin D3 administered before fractionated RT to significantly reduce the RT-induced epiphyseal injury. Key words: Vitamin D3, radiotherapy, rat, epiphyseal injury, radioprotection.