BackgroundWhile careful planning and pre‐treatment checks are performed to ensure patient safety during external beam radiation therapy (EBRT), inevitable daily variations mean that in vivo dosimetry (IVD) is the only way to attain the true delivered dose. Several countries outside the US require daily IVD for quality assurance. However, elsewhere, the manual labor and time considerations of traditional in vivo dosimeters may be preventing frequent use of IVD in the clinic.PurposeThis study expands upon previous research using plastic scintillator discs for optical dosimetry for electron therapy treatments. We present the characterization of scintillator discs for in vivo x‐ray dosimetry and describe additional considerations due to geometric complexities.MethodsPlastic scintillator discs were coated with reflective white paint on all sides but the front surface. An anti‐reflective, matte coating was applied to the transparent face to minimize specular reflection. A time‐gated iCMOS camera imaged the discs under various irradiation conditions. In post‐processing, background‐subtracted images of the scintillators were fit with Gaussian‐convolved ellipses to extract several parameters, including integral output, and observation angle.ResultsDose linearity and x‐ray energy independence were observed, consistent with ideal characteristics for a dosimeter. Dose measurements exhibited less than 5% variation for incident beam angles between 0° and 75° at the anterior surface and 0–60 at the posterior surface for exit beam dosimetry. Varying the angle between the disc surface and the camera lens did not impact the integral output for the same dose up to 55°. Past this point, up to 75°, there is a sharp falloff in response; however, a correction can be used based on the detected width of the disc. The reproducibility of the integral output for a single disc is 2%, and combined with variations from the gantry angle, we report the accuracy of the proposed scintillator disc dosimeters as ±5.4%.ConclusionsPlastic scintillator discs have characteristics that are well‐suited for in vivo optical dosimetry for x‐ray radiotherapy treatments. Unlike typical point dosimeters, there is no inherent readout time delay, and an optical recording of the measurement is saved after treatment for future reference. While several factors influence the integral output for the same dose, they have been quantified here and may be corrected in post‐processing.

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技术说明：用于体内 MV 光子束放射治疗的视觉、快速、闪烁点剂量测定

背景虽然在外照射放射治疗 (EBRT) 期间进行了仔细的计划和治疗前检查以确保患者安全，但不可避免的日常变化意味着体内剂量测定 (IVD) 是获得真实递送剂量的唯一方法。美国以外的一些国家/地区要求每天进行 IVD 以保证质量。然而，在其他地方，传统体内剂量计的体力劳动和时间考虑可能会阻碍体外诊断在临床中的频繁使用。目的本研究扩展了先前使用塑料闪烁盘进行电子治疗光学剂量测定的研究。我们介绍了用于体内 X 射线剂量测定的闪烁体盘的特征，并描述了由于几何复杂性而需要考虑的其他因素。方法塑料闪烁体盘除前表面外的所有侧面均涂有反射白色涂料。透明面上涂有抗反射哑光涂层，以最大限度地减少镜面反射。时间选通 iCMOS 相机在不同的照射条件下对光盘进行成像。在后处理中，闪烁体的背景扣除图像与高斯卷积椭圆拟合，以提取多个参数，包括积分输出和观察角度。结果观察到剂量线性和 X 射线能量独立性，与剂量计的理想特性一致。对于出射光束剂量测定，前表面 0° 至 75° 之间的入射光束角度和后表面 0–60° 之间的入射光束角度的剂量测量显示小于 5% 的变化。对于相同剂量（高达 55°），改变圆盘表面和相机镜头之间的角度不会影响积分输出。超过此点（直至 75°），响应会急剧下降；然而，可以基于检测到的盘宽度进行校正。单个圆盘的积分输出的再现性为 2%，并结合机架角度的变化，我们报告所提出的闪烁体圆盘剂量计的精度为 ±5.4%。 结论塑料闪烁体圆盘具有非常适合在用于 X 射线放射治疗的体内光学剂量测定。与典型的点剂量计不同，它没有固有的读出时间延迟，并且在治疗后保存测量的光学记录以供将来参考。虽然有几个因素会影响相同剂量的积分输出，但它们已在此处进行了量化，并且可以在后处理中进行纠正。