Department of Radiation Oncology, Tokyo Women's Medical University, Shinjuku-ku, Tokyo, Japan.
Department of Medical Physics, Tokyo Women's Medical University, Shinjuku-ku, Tokyo, Japan.
Med Phys. 2021 Oct;48(10):5639-5650. doi: 10.1002/mp.15164. Epub 2021 Aug 20.
To test the measurement technique of the three-dimensional (3D) dose distribution measured image by capturing the scintillation light generated using a plastic scintillator and a scintillating screen.
Our imaging system constituted a column shaped plastic scintillator covered by a Gd O S:Tb scintillating screen, a conical mirror and a cooled CCD camera. The scintillator was irradiated with 6 MV photon beams. Meanwhile, the irradiated plan was prepared for the static field plans, two-field plan (2F plan) and the conformal arc plan (CA plan). The 2F plan contained 16 mm and 10 mm fields irradiated from gantry angles of 0° and 25°, respectively. The gantry was rotated counterclockwise from 45° to 315° for the CA plan. The field size was then obtained as 10 mm . A Monte Carlo simulation was performed in the experimental geometry to obtain the calculated 3D dose distribution as the reference data. Dose response was acquired by comparing between the reference and the measurement. The dose rate dependence was verified by irradiating the same MU value at different dose rates ranging from 100 to 600 MU/min. Deconvolution processing was applied to the measured images for the correction of light blurring. The measured 3D dose distribution was reconstructed from each measured image. Gamma analysis was performed to these 3D dose distributions. The gamma criteria were 3% for the dose difference, 2 mm for the distance-to-agreement and 10% for the threshold.
Dose response for the scintillation light was linear. The variation in the light intensity for the dose rate ranging from 100 to 600 MU/min was less than 0.5%, while our system presents dose rate independence. For the 3D dose measurement, blurring of light through deconvolution processing worked well. The 3D gamma passing rate (3D GPR) for the 10 × 10 mm , 16 × 16 mm , and 20 × 20 mm fields were observed to be 99.3%, 98.8%, and 97.8%, respectively. Reproducibility of measurement was verified. The 3D GPR results for the 2F plan and the CA plan were 99.7% and 100%, respectively.
We developed a plastic scintillation dosimeter and demonstrated that our system concept can act as a suitable technique for measuring the 3D dose distribution from the gamma results. In the future, we will attempt to measure the 4D dose distribution for clinical volumetric modulated arc radiation therapy (VMAT)-SBRTplans.
测试通过捕获使用塑料闪烁体和闪烁屏产生的闪烁光来测量三维（3D）剂量分布的测量技术。
我们的成像系统由一个圆柱形塑料闪烁体组成，该闪烁体覆盖有 Gd O S：Tb 闪烁屏、一个锥形镜和一个冷却的 CCD 相机。闪烁体受到 6MV 光子束的照射。同时，为静态场计划、两野计划（2F 计划）和适形弧计划（CA 计划）准备了照射计划。2F 计划包含分别从 0°和 25°机架角度照射的 16mm 和 10mm 野。从 45°逆时针旋转机架角度进行 CA 计划，得到 10mm 的射野。在实验几何形状中进行了蒙特卡罗模拟，以获得作为参考数据的计算三维剂量分布。通过比较参考数据和测量数据来获取剂量响应。通过在从 100 到 600MU/min 的不同剂量率下照射相同 MU 值来验证剂量率依赖性。对测量图像进行反卷积处理，以校正光模糊。从每个测量图像重建测量的 3D 剂量分布。对这些 3D 剂量分布进行伽马分析。伽马标准为剂量差 3%，距离一致 2mm，阈值 10%。
闪烁光的剂量响应是线性的。在 100 至 600MU/min 的剂量率范围内，光强度的变化小于 0.5%，而我们的系统呈现剂量率独立性。对于 3D 剂量测量，通过反卷积处理的光模糊校正效果良好。对于 10×10mm、16×16mm 和 20×20mm 射野，3D 伽马通过率（3D GPR）分别为 99.3%、98.8%和 97.8%。测量的可重复性得到验证。2F 计划和 CA 计划的 3D GPR 结果分别为 99.7%和 100%。
我们开发了一种塑料闪烁体剂量计，并证明我们的系统概念可以作为一种合适的技术，从伽马结果测量 3D 剂量分布。在未来，我们将尝试测量临床容积调制弧形放射治疗（VMAT）-SBRT 计划的 4D 剂量分布。
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