The effect of altered fractionation schedule on the spinal cord response: radiobiological considerations
Abstract
Increased fractionation spares late reacting normal tissues more than acute reacting normal tissues. A linear quadratic model is valid from large dose per fraction down to dose per fraction of 2 Gy. Experimental studies on animals and clinical studies on the spinal cord tolerance have shown incidences of myelopathy at doses lower than 50 Gy. The α/β value of the linear quadratic model have been lower for low doses per fraction, indicating a sparing effect of altered fractionation for spinal cord myelitis. Animal data, clinical and radiobiological explanations suggest limitation of the radiobiological models. Further data suggest that one must not assume the spinal cord to have a greater tolerance at doses per fraction below the conventional dose per fraction of 2 Gy.