Hyperfractionation decreases the deleterious effects of conventional radiation fractionation on vertebral growth in animals.

Craniospinal axis irradiation in the treatment of pediatric tumors is associated with serious long-term sequelae including decreased bone growth (short sitting stature). In this study, an animal model was used to determine the effects of smaller incremental doses of radiation on bone growth. Sprague-Dawley weanling rats were given 25 Gy to the spine in 8 to 9 days, with fraction sizes ranging from 1.0 to 1.8 Gy. The animals receiving smaller doses per fraction (1.0 or 1.25 Gy) showed significantly more growth of the vertebral bodies in the treated fields than animals given larger incremental doses (1.5 or 1.8 Gy). These findings indicate a protective effect on bone growth for hyperfractionated irradiation of vertebral bodies.