Thayer School of Engineering, Dartmouth College, Hanover, NH, USA.
Department of Radiation Oncology, Brigham and Women's Hospital, Dana Farber Cancer Institute, Boston, MA, USA.
Med Phys. 2019 Aug;46(8):3674-3678. doi: 10.1002/mp.13637. Epub 2019 Jun 25.
The aim of this study was to create an optical imaging-based system for quality assurance (QA) testing of a dedicated Co-60 total body irradiation (TBI) machine. Our goal is to streamline the QA process by minimizing the amount time necessary for tests such as verification of dose rate and field homogeneity.
Plastic scintillating rods were placed directly on the patient treatment couch of a dedicated TBI Co irradiator. A tripod-mounted intensified camera was placed directly adjacent to the couch. Images were acquired over a 30-s period once the cobalt source was fully exposed. Real-time image filtering was used; cumulative images were flatfield corrected as well as background and darkfield subtracted. Scintillators were used to measure light-radiation field correspondence, dose rate, field homogeneity, and symmetry. Dose rate effects were measured by modifying the height of the treatment couch and scintillator response was compared to ionization chamber (IC) measurements. Optically stimulated luminesce detector (OSLD) used as reference dosimeters during field symmetry and homogeneity testing.
The scintillator-based system accurately reported changes in dose rate. When comparing normalized output values for IC vs scintillators over a range of source-to-surface distances, a linear relationship (R = 0.99) was observed. Normalized scintillator signal matched OSLD measurements with <1.5% difference during field homogeneity and symmetry testing. Beam symmetry across both axes of the field was within 2%. The light field was found to correspond to 90 ± 3% of the isodose maximum along the longitudinal and latitudinal axis, respectively. Scintillator imaging output results using a single image stack requiring no postexposure processing (needed for OSLD) or repeat manual measurements (needed for IC).
Imaging of scintillation light emission from plastic rods is a viable and efficient method for carrying out TBI Co irradiator QA. We have shown that this technique can accurately measure field homogeneity, symmetry, light-radiation field correspondence, and dose rate effects.
本研究旨在创建一个基于光学成像的质量保证（QA）测试系统，用于专用钴-60 全身辐照（TBI）机。我们的目标是通过最小化剂量率验证和场均匀性等测试所需的时间，简化 QA 流程。
将塑料闪烁体棒直接放置在专用 TBI 钴辐照器的患者治疗台上。将三脚架安装的增强型相机直接放置在治疗台旁边。钴源完全暴露后，在 30 秒内采集图像。实时图像滤波；累积图像进行了平面场校正以及背景和暗场扣除。闪烁体用于测量光辐射场对应、剂量率、场均匀性和对称性。通过改变治疗台的高度来测量剂量率效应，并将闪烁体的响应与电离室（IC）测量进行比较。在进行场对称性和均匀性测试时，使用光激励发光探测器（OSLD）作为参考剂量计。
基于闪烁体的系统准确报告了剂量率的变化。当比较 IC 和闪烁体在源到表面距离范围内的归一化输出值时，观察到线性关系（R=0.99）。在进行场均匀性和对称性测试时，归一化闪烁体信号与 OSLD 测量值相差小于 1.5%。在两个场轴上的光束对称性均在 2%以内。在纵向和横向轴上，光场分别与等剂量最大值的 90±3%相对应。使用单个图像堆栈进行闪烁体成像输出结果，无需进行后曝光处理（OSLD 需要）或重复手动测量（IC 需要）。
塑料棒闪烁光发射的成像，是进行 TBI 钴辐照器 QA 的一种可行且高效的方法。我们已经证明，该技术可以准确测量场均匀性、对称性、光辐射场对应和剂量率效应。
