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首页> 外文期刊>Radiotherapy and oncology: Journal of the European Society for Therapeutic Radiology and Oncology >The use of an aSi-based EPID for routine absolute dosimetric pre-treatment verification of dynamic IMRT fields.
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The use of an aSi-based EPID for routine absolute dosimetric pre-treatment verification of dynamic IMRT fields.

机译：基于aSi的EPID用于动态IMRT场的常规绝对剂量预处理验证。

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BACKGROUND AND PURPOSE: In parallel with the increased use of intensity modulated radiation treatment (IMRT) fields in radiation therapy, flat panel amorphous silicon (aSi) detectors are becoming the standard for online portal imaging at the linear accelerator. In order to minimise the workload related to the quality assurance of the IMRT fields, we have explored the possibility of using a commercially available aSi portal imager for absolute dosimetric verification of the delivery of dynamic IMRT fields. PATIENTS AND METHODS: We investigated the basic dosimetric characteristics of an aSi portal imager (aS500, Varian Medical Systems), using an acquisition mode especially developed for portal dose (PD) integration during delivery of a-static or dynamic-radiation field. Secondly, the dose calculation algorithm of a commercially available treatment planning system (Cadplan, Varian Medical Systems) was modified to allow prediction of the PD image, i.e. to compare the intended fluence distribution with the fluence distribution as actually delivered by the dynamic multileaf collimator. Absolute rather than relative dose prediction was applied. The PD image prediction was compared to the corresponding acquisition for several clinical IMRT fields by means of the gamma evaluation method. RESULTS AND CONCLUSIONS: The acquisition mode is accurate in integrating all PD over a wide range of monitor units, provided detector saturation is avoided. Although the dose deposition behaviour in the portal image detector is not equivalent to the dose to water measurements, it is reproducible and self-consistent, lending itself to quality assurance measurements. Gamma evaluations of the predicted versus measured PD distribution were within the pre-defined acceptance criteria for all clinical IMRT fields, i.e. allowing a dose difference of 3% of the local field dose in combination with a distance to agreement of 3 mm.
机译：背景和目的：在放射治疗中增加使用强度调制放射治疗（IMRT）领域的同时，平板非晶硅（aSi）检测器正成为线性加速器在线门户成像的标准。为了最大程度地减少与IMRT场质量保证相关的工作量，我们探索了使用商用aSi门户成像仪对动态IMRT场的交付进行绝对剂量验证的可能性。病人和方法：我们使用了一种专为在非静态或动态辐射场输送过程中整合门户剂量（PD）而开发的采集模式，研究了aSi门户成像器（aS500，Varian Medical Systems）的基本剂量特性。其次，对市售治疗计划系统（Cadplan，Varian Medical Systems）的剂量计算算法进行了修改，以允许对PD图像进行预测，即将预期通量分布与动态多叶准直仪实际输送的通量分布进行比较。应用绝对剂量而非相对剂量预测。通过伽玛评估方法，将PD图像预测与几个临床IMRT领域的相应采集进行了比较。结果与结论：在避免检测器饱和的情况下，采集模式可以准确地将所有PD集成到各种监视单元中。尽管在门户图像检测器中的剂量沉积行为不等同于水的剂量测量，但它具有可重现性和自洽性，可用于质量保证测量。对所有临床IMRT视野的预测PD分布与测量PD分布的伽马评估均在预定义的接受标准之内，即允许局部视野剂量的3％的剂量差异与3 mm的一致距离相结合。

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