Minimal difference between fractionated and single-fraction exposure in a murine model of radiation necrosis

Despite the success of fractionation in clinical practice to spare healthy tissue, it remains common for mouse models used to study the efficacy of radiation therapy to use minimal or no fractionation. The goal of our study was to create a fractionated mouse model of radiation necrosis that we could compare to our single fraction model.

Precision X-Ray's X-Rad 320 cabinet irradiator was used to irradiate the cerebrum of mice with four different fractionation schemes, while a 7 T Bruker magnetic resonance imaging (MRI) scanner using T2 and post-contrast T1 imaging was used to track the development of radiation necrosis over the span of six weeks.

All four fractionation schemes with single fraction equivalent doses (SFED) less than 50 Gy for the commonly accepted alpha/beta ratio (α/β) value of 2-3 Gy produced radiation necrosis comparable to what would be achieved with single fraction doses of 80 and 90 Gy. This is surprising when previous work using single fractions of 50 Gy produced no visible radiation necrosis, with the results of this study showing fractionation not sparing brain tissue as much as expected.

Further interpretation of these results must take into consideration other studies which have shown a lack of sparing when fractionation has been incorporated, as well as consider factors such as the use of large doses per fraction, the time between fractions, and the limitations of using a murine model to analyze the human condition.