Department of Nuclear and Radiological Engineering, University of Florida, Gainesville, Florida 32611-8300, USA.
Med Phys. 2010 Jan;37(1):108-15. doi: 10.1118/1.3266769.
The aim of this work is to develop effective calibration methods for a novel fourdimensional (4D) diode array for pretreatment verification of intensity-modulated radiation therapy (IMRT) and rotational therapy.
A novel 4D diode array (ArcCHECK, Sun Nuclear, Melbourne, FL) was developed to meet the needs of appropriate and efficient quality assurance for IMRT and especially rotational radiotherapy. The diode array presents a consistent detector image in beam's eye view at arbitrary gantry angles due to isotropic arrangement of diodes in a three-dimensional (3D) cylindrical phantom. The 50 ms simultaneous update of all diodes on the detector array (fourth dimension) makes it capable of time-resolved beam delivery analysis with any rotational delivery techniques. The calibration procedure consisted of delivering and measuring a series of calibration beams with 5.8 degrees angular spacing surrounding the cylindrical diode array. Correction factors for diode intrinsic sensitivity and directional response dependence were derived from these measurements. A real-time algorithm to derive gantry angles based on the detector signal was developed to interpolate and apply the corresponding angular correction factors.
The calibration was validated with ion chamber scanned beam profiles in a 3D water tank. Excellent agreement was observed between diode array measurement and treatment planning system calculation. The accuracy of the gantry angle derivation algorithm was within 1 degree which caused a less than 0.2% dosimetric uncertainty.
With the proposed calibration method and the automatic gantry angle derivation algorithm, the 4D diode array achieved isotropic detector response and is suitable for both IMRT and rotational therapy pretreatment verification.
本研究旨在开发一种新颖的四维（4D）二极管阵列的有效校准方法，用于强度调制放射治疗（IMRT）和旋转治疗的预处理验证。
为了满足 IMRT 特别是旋转放射治疗的适当和高效质量保证的需求，开发了一种新颖的 4D 二极管阵列（ArcCHECK，Sun Nuclear，墨尔本，FL）。由于在三维（3D）圆柱形体模中各向同性排列的二极管，二极管阵列在任意旋转机架角度下呈现一致的射束眼视图探测器图像。由于探测器阵列上所有二极管的 50 毫秒的同步更新（第四个维度），它可以使用任何旋转输送技术进行时间分辨的束流输送分析。校准程序包括输送和测量一系列校准束，这些校准束具有围绕圆柱形二极管阵列的 5.8 度角间距。从这些测量中得出了二极管固有灵敏度和方向响应依赖性的校正因子。开发了一种基于探测器信号的实时算法来推导旋转机架角度，以插值和应用相应的角度校正因子。
通过在 3D 水箱中的离子室扫描束流剖面验证了校准。在二极管阵列测量和治疗计划系统计算之间观察到极好的一致性。旋转机架角度推导算法的精度在 1 度以内，这导致剂量学不确定性小于 0.2%。
采用所提出的校准方法和自动旋转机架角度推导算法，4D 二极管阵列实现了各向同性探测器响应，适用于 IMRT 和旋转治疗的预处理验证。
