Yock Adam D, Johnson Levi S, Price Michael
Department of Radiation Oncology, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
Phys Imaging Radiat Oncol. 2020 Jun 11;14:67-73. doi: 10.1016/j.phro.2020.06.001. eCollection 2020 Apr.
Conical scintillation detectors are frequently used to measure geometric characteristics of radiotherapy modalities. However, their application to verify intensity-modulated radiotherapy plan delivery has not been investigated and requires a more detailed understanding of device response. This work evaluated the novel application of a conical scintillation detector to plan-specific quality assurance (QA) for intensity-modulated photon plans by evaluating device dependence on beam delivery and device acquisition parameters.
Measurements were made with a conical scintillation detector using beam delivery parameters of five photon beams (6-15 MV, including flattening filter free), three field sizes (1 × 1-5 × 5 cm), and several dose rates (100-2000 MU/min) combined with device acquisition parameters of two frame rates (10 and 20 fps) and three gains (18-22 dB). A standardization equation to correct for gain and frame rate was investigated, and the remaining dose rate dependence was characterized. Device precision was evaluated using replicate measurements, and spatial uniformity was determined by irradiating different parts of the device.
For each parameter combination, measurement reproducibility was 1.3%, and spatial uniformity was 1-2%. Scintillation intensity varied with gain, frame rate, and dose rate. Standardizing measurements for gain and frame rate was effective, but a dependence on dose rate caused errors at non-reference conditions (root mean squared error, RMSE: 0-152%). An additional dose rate correction specific to each combination of gain and frame rate improved accuracy (RMSE 0-17%).
To consider the detector for plan-specific QA of intensity-modulated radiotherapy plans, correction factors are imperative to mitigate effects of delivery and acquisition parameters.
锥形闪烁探测器常用于测量放射治疗方式的几何特征。然而，其在验证调强放射治疗计划传输方面的应用尚未得到研究，需要更详细地了解设备响应。本研究通过评估设备对射束传输和设备采集参数的依赖性，对锥形闪烁探测器在调强光子计划的特定计划质量保证（QA）中的新应用进行了评估。
使用锥形闪烁探测器进行测量，采用了五种光子束（6 - 15 MV，包括无均整器）的射束传输参数、三种射野尺寸（1×1 - 5×5 cm）以及几种剂量率（100 - 2000 MU/分钟），并结合两种帧率（10和20 fps）和三种增益（18 - 22 dB）的设备采集参数。研究了一个用于校正增益和帧率的标准化方程，并对剩余的剂量率依赖性进行了表征。通过重复测量评估设备精度，通过照射设备的不同部位确定空间均匀性。
对于每种参数组合，测量重复性为1.3%，空间均匀性为1 - 2%。闪烁强度随增益、帧率和剂量率而变化。对增益和帧率进行测量标准化是有效的，但在非参考条件下剂量率依赖性会导致误差（均方根误差，RMSE：0 - 152%）。针对每种增益和帧率组合的额外剂量率校正提高了准确性（RMSE 0 - 17%）。
为了将该探测器用于调强放射治疗计划的特定计划QA，校正因子对于减轻传输和采集参数的影响至关重要。
