Department of Medical Biophysics, The University of Western Ontario, 1151 Richmond Street, London, Ontario N6A 3K7, Canada.
Med Phys. 2013 Aug;40(8):081706. doi: 10.1118/1.4812422.
To design, construct, and commission a set of computer-controlled motorized jaws for a micro-CT∕RT system to perform conformal image-guided small animal radiotherapy.
The authors designed and evaluated a system of custom-built motorized orthogonal jaws, which allows the delivery of off-axis rectangular fields on a GE eXplore CT 120 preclinical imaging system. The jaws in the x direction are independently driven, while the y-direction jaws are symmetric. All motors have backup encoders, verifying jaw positions. Mechanical performance of the jaws was characterized. Square beam profiles ranging from 2×2 to 60×60 mm2 were measured using EBT2 film in the center of a 70×70×22 mm3 solid water block. Similarly, absolute depth dose was measured in a solid water and EBT2 film stack 50×50×50 mm3. A calibrated Farmer ion chamber in a 70×70×20 mm3 solid water block was used to measure the output of three field sizes: 50×50, 40×40, and 30×30 mm2. Elliptical target plans were delivered to films to assess overall system performance. Respiratory-gated treatment was implemented on the system and initially proved using a simple sinusoidal motion phantom. All films were scanned on a flatbed scanner (Epson 1000XL) and converted to dose using a fitted calibration curve. A Monte Carlo beam model of the micro-CT with the jaws has been created using BEAMnrc for comparison with the measurements. An example image-guided partial lung irradiation in a rat is demonstrated.
The averaged random error of positioning each jaw is less than 0.1 mm. Relative output factors measured with the ion chamber agree with Monte Carlo simulations within 2%. Beam profiles and absolute depth dose curves measured from the films agree with simulations within measurement uncertainty. Respiratory-gated treatments applied to a phantom moving with a peak-to-peak amplitude of 5 mm showed improved beam penumbra (80%-20%) from 3.9 to 0.8 mm.
A set of computer-controlled motorized jaws for a micro-CT∕RT system were constructed with position reliably better than a tenth of a millimeter. The hardware system is ready for image-guided conformal radiotherapy for small animals with capability of respiratory-gated delivery.
设计、构建和调试一套用于微 CT/RT 系统的计算机控制的电动 jaws，以进行适形图像引导的小动物放射治疗。
作者设计并评估了一套定制的电动正交 jaws 系统，该系统允许在 GE eXplore CT 120 临床前成像系统上提供非共面矩形野。x 方向的 jaws 独立驱动，而 y 方向的 jaws 对称。所有电机都有备份编码器，可验证 jaws 位置。用 EBT2 胶片测量了 70×70×22mm3 实心水块中心的 2×2 至 60×60mm2 的方形射束轮廓。同样，在实心水和 EBT2 胶片堆 50×50×50mm3 中测量了绝对深度剂量。在 70×70×20mm3 实心水块中使用校准的 Farmer 离子室测量了三个射野尺寸的输出：50×50、40×40 和 30×30mm2。将椭圆形靶计划输送到胶片上以评估整个系统的性能。在系统上实施了呼吸门控治疗，并使用简单的正弦运动体模初步证明了该系统的性能。所有胶片均在平板扫描仪（Epson 1000XL）上扫描，并使用拟合的校准曲线转换为剂量。使用 BEAMnrc 为微 CT 与 jaws 创建了蒙特卡罗束模型，以便与测量结果进行比较。展示了一例在大鼠中进行的图像引导的部分肺照射的实例。
每个 jaws 的定位随机误差平均值小于 0.1mm。用离子室测量的相对输出因子与蒙特卡罗模拟值的差值在 2%以内。从胶片测量的射束轮廓和绝对深度剂量曲线与模拟值的差值在测量不确定度范围内。应用于具有 5mm 峰峰值幅度的体模的呼吸门控治疗显示出射束半影（80%-20%）从 3.9mm 改善至 0.8mm。
构建了一套用于微 CT/RT 系统的计算机控制的电动 jaws，其位置精度可靠地优于十分之一毫米。该硬件系统已准备好用于小动物的图像引导适形放射治疗，具有呼吸门控输送的能力。
