School of Health Sciences, Purdue University, 550 Stadium Mall Drive, Hampton Hall 1263A, West Lafayette, IN, 47907, USA.
Purdue University Center for Cancer Research, Purdue University, West Lafayette, IN, USA.
Radiat Oncol. 2019 Aug 13;14(1):144. doi: 10.1186/s13014-019-1356-3.
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.
尽管分次治疗在临床实践中成功地保护了健康组织，但用于研究放射治疗疗效的小鼠模型通常仍采用最小或无分次治疗。我们的研究目的是建立一种放射性坏死的分次小鼠模型，以便与我们的单次照射模型进行比较。
使用 Precision X-Ray 的 X-Rad 320 箱式辐照仪对小鼠的大脑进行 4 种不同的分次方案照射，同时使用 7T Bruker 磁共振成像（MRI）扫描仪进行 T2 和对比后 T1 成像，以在 6 周的时间内跟踪放射性坏死的发展。
4 种分次方案的单次照射等效剂量（SFED）均小于 50Gy，对于常用的 2-3Gy 的α/β比值（α/β）值，产生的放射性坏死与 80Gy 和 90Gy 的单次照射剂量相当。当使用 50Gy 的单次照射剂量时，先前的研究没有产生可见的放射性坏死，而这项研究的结果表明，分次治疗并没有像预期的那样保护脑组织，这令人惊讶。
进一步解释这些结果时必须考虑到其他研究表明，当采用分次治疗时，并没有节省组织，并且还需要考虑到每个分次剂量较大、分次之间的时间间隔以及使用小鼠模型来分析人类状况的局限性等因素。
