Department of Health Sciences and Technology, SAIHST, Sungkyunkwan University, Seoul, Korea.
Proton Therapy Center, National Cancer Center, Goyang, Korea.
PLoS One. 2021 Feb 12;16(2):e0246742. doi: 10.1371/journal.pone.0246742. eCollection 2021.
We developed a compact and lightweight time-resolved mirrorless scintillation detector (TRMLSD) employing image processing techniques and a convolutional neural network (CNN) for high-resolution two-dimensional (2D) dosimetry.
The TRMLSD comprises a camera and an inorganic scintillator plate without a mirror. The camera was installed at a certain angle from the horizontal plane to collect scintillation from the scintillator plate. The geometric distortion due to the absence of a mirror and camera lens was corrected using a projective transform. Variations in brightness due to the distance between the image sensor and each point on the scintillator plate and the inhomogeneity of the material constituting the scintillator were corrected using a 20.0 × 20.0 cm2 radiation field. Hot pixels were removed using a frame-based noise-reduction technique. Finally, a CNN-based 2D dose distribution deconvolution model was applied to compensate for the dose error in the penumbra region and a lack of backscatter. The linearity, reproducibility, dose rate dependency, and dose profile were tested for a 6 MV X-ray beam to verify dosimeter characteristics. Gamma analysis was performed for two simple and 10 clinical intensity-modulated radiation therapy (IMRT) plans.
The dose linearity with brightness ranging from 0.0 cGy to 200.0 cGy was 0.9998 (R-squared value), and the root-mean-square error value was 1.010. For five consecutive measurements, the reproducibility was within 3% error, and the dose rate dependency was within 1%. The depth dose distribution and lateral dose profile coincided with the ionization chamber data with a 1% mean error. In 2D dosimetry for IMRT plans, the mean gamma passing rates with a 3%/3 mm gamma criterion for the two simple and ten clinical IMRT plans were 96.77% and 95.75%, respectively.
The verified accuracy and time-resolved characteristics of the dosimeter may be useful for the quality assurance of machines and patient-specific quality assurance for clinical step-and-shoot IMRT plans.
我们开发了一种紧凑、轻便的时间分辨无镜闪烁探测器（TRMLSD），采用图像处理技术和卷积神经网络（CNN）进行高分辨率二维（2D）剂量测定。
TRMLSD 包括一个相机和一个没有镜子的无机闪烁体板。相机安装在离水平面一定角度的位置，以收集来自闪烁体板的闪烁。由于没有镜子和相机镜头而产生的几何变形，通过投影变换进行校正。由于图像传感器与闪烁体板上各点之间的距离以及构成闪烁体的材料的不均匀性而导致的亮度变化，通过 20.0×20.0cm2 的辐射场进行校正。使用基于帧的降噪技术去除热点像素。最后，应用基于 CNN 的 2D 剂量分布反卷积模型来补偿半影区域和缺乏后散射的剂量误差。为了验证剂量计的特性，对 6MV X 射线束进行了线性度、重现性、剂量率依赖性和剂量分布测试。对两个简单和 10 个临床强度调制放射治疗（IMRT）计划进行了伽马分析。
亮度在 0.0 cGy 至 200.0 cGy 范围内的剂量线性度为 0.9998（R 平方值），均方根误差值为 1.010。对于连续五次测量，重现性在 3%误差范围内，剂量率依赖性在 1%以内。深度剂量分布和侧向剂量分布与电离室数据吻合，平均误差为 1%。在 IMRT 计划的 2D 剂量测定中，对于两个简单和十个临床 IMRT 计划，使用 3%/3mm 伽玛标准的平均伽玛通过率分别为 96.77%和 95.75%。
该剂量计的验证准确性和时间分辨特性可能对机器的质量保证和临床分步 IMRT 计划的患者特定质量保证有用。
