Leksell γ射线三维剂量测量系统的研制
Development of a 3-Dimensional Dosimetry System for Leksell Gamma Knife-Perfexion
摘要：
本研究的目的是开发一种新的三维剂量测定系统，以验证Leksell Gamma Enhancefe-PerfectTM（LGKP）（Elekta，Norcross，GA，USA）中剂量输送的准确性。该仪器由一个移动的头部幻影，一个嵌入式薄活性层和一个CCD相机系统，并被设计为安装到LGKP。作为活性材料同心地位于半球形头部模型中，我们选择Gafchromic EBT 3薄膜和Gd_2 O_2S;Tb荧光片进行剂量测量。此外，为了补偿反向散射的缺乏，我们在有源层的下游放置了1 cm厚的PMMA板。PMMA板对于闪烁光是透明的，以到达具有1200 × 1200像素、间距为5.2 μ m的CCD。使用该系统，在三种准直器设置（即，分别为4 mm、8 mm和16 mm）中的每一种下，通过0.2mm切片间隙采集300幅图像。在相同条件下，将CCD摄像机拍摄的二维投影图像与EBT 3胶片测量的剂量分布进行了比较。所有2D分布通过拟合每个准直器设置的峰值得出的最大值进行归一化。CCD图像和胶片剂量之间的2D轮廓的半高宽差异被测量为小于0.3 mm。整个峰区域的扫描任务用新仪器不到三分钟。它可以作为伽玛刀放射外科系统的质量保证工具，而不是胶片剂量学，使用它需要更多的时间和资源。
英文摘要：
The purpose of our study is to develop a new, 3-dimensional dosimetry system to verify the accuracy of dose deliveries in Leksell Gamma Knife-Perfexion TM (LGKP) (Elekta, Norcross, GA, USA). The instrument consists of a moving head phantom, an embedded thin active layer and a CCD camera system and was designed to be mounted to LGKP. As an active material concentrically located in the hemispheric head phantom, we choose Gafchromic EBT3 films and Gd2O2S;Tb phosphor sheets for dosimetric measurements. Also, to compensate the lack of backscatter, we located a 1 cm thick PMMA plate downstream of the active layer. The PMMA plate was transparent for scintillation lights to reach the CCD with 1200x1200 pixels by a 5.2 um pitch. Using this system, three hundred images by a 0.2 mm slice gap were acquired under each of three collimator setups, i.e. 4 mm, 8 mm, and 16 mm, respectively. The 2D projected images taken by CCD camera were compared with the dose distributions measured by EBT3 films in the same conditions. All 2D distributions were normalized by the maximum values derived by fitting peaks for each collimator setup. The FWHM differences of 2D profiles between of CCD images and of film doses were measured to be less than 0.3 mm. The scanning task for whole peak regions took less than three minutes with the new instrument. It could be utilized as a QA tool for the Gamma Knife radiosurgery system instead of film dosimetry, the use of which requires much more time and resources.
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