Guerrero M, Li X Allen
Department of Radiation Oncology, University of Maryland, Baltimore, MD 21201, USA.
Phys Med Biol. 2004 Oct 21;49(20):4825-35. doi: 10.1088/0031-9155/49/20/012.
Ongoing clinical trials designed to explore the use of extracranial stereotactic radiosurgery (ESR) for different tumour sites use large doses per fraction (15, 20, 30 Gy or even larger). The question of whether the linear-quadratic (LQ) model is appropriate to describe radiation response for such large fraction doses has been raised and has not been answered definitively. It has been proposed that mechanism-based models, such as the lethal-potentially lethal (LPL) model, could be more appropriate for such large fraction/acute doses. However, such models are not well characterized with clinical data and they are generally not easy to use. The purpose of this work is to modify the LQ model to more accurately describe radiation response for high fraction/acute doses. A new parameter is introduced in the modified LQ (MLQ) model. The new parameter introduced is characterized based both on in vitro cell survival data of several human tumour cell lines and in vivo animal iso-effect curves. The MLQ model produces a better fit to the iso-effect data than the LQ model. For a high single dose irradiation, the prediction of the MLQ is consistent with that from the LPL model. Unlike the LPL model, the MLQ model retains the simplicity of the LQ model and uses the well-characterized alpha and beta parameters. This work indicates that the standard LQ model can lead to erroneous results when used to calculate iso-effects with large fraction doses, such as those used for ESR. We present a solution to this problem.
目前正在进行的旨在探索将颅外立体定向放射治疗（ESR）用于不同肿瘤部位的临床试验，每次分割使用大剂量（15、20、30 Gy甚至更大）。关于线性二次（LQ）模型是否适合描述如此大分割剂量的辐射反应这一问题已经被提出，但尚未得到明确解答。有人提出，基于机制的模型，如致死-潜在致死（LPL）模型，可能更适合如此大分割/急性剂量。然而，此类模型尚未通过临床数据充分表征，而且通常不易使用。这项工作的目的是修改LQ模型，以更准确地描述高分次/急性剂量的辐射反应。在修改后的LQ（MLQ）模型中引入了一个新参数。引入的新参数是基于几种人类肿瘤细胞系的体外细胞存活数据和体内动物等效效应曲线来表征的。与LQ模型相比，MLQ模型对等效效应数据的拟合更好。对于高单次剂量照射，MLQ模型的预测与LPL模型的预测一致。与LPL模型不同，MLQ模型保留了LQ模型的简单性，并使用了特征明确的α和β参数。这项工作表明，当使用标准LQ模型计算大分割剂量（如用于ESR的剂量）的等效效应时，可能会得出错误结果。我们提出了这个问题的解决方案。
