用于带图像引导的微辐照器的临床前剂量学的闪烁光纤探测器的能量依赖性。

Grand accélérateur National d'Ions Lourds (GANIL), CEA/DRF-CNRS/IN2P3, Boulevard Henri Becquerel, 14076 Caen, France. Author to whom any correspondence should be addressed.

Phys Med Biol. 2019 May 29;64(11):115015. doi: 10.1088/1361-6560/ab1854.

The dosimetry of preclinical micro-irradiators is challenging due to their millimetric beams and medium x-ray energy range. Plastic scintillator dosimeters (PSD) are good candidates for such a purpose as they provide a high spatial resolution although they show an energy dependence below 100 keV. The purpose of this study was to assess the energy dependence of a dedicated PSD (called DosiRat) for micro-irradiators dosimetry. The response of the PSD relative to air kerma was measured for different beam qualities (40-225 kV) with the X-RAD 225Cx irradiator. The corresponding energy spectra, determined by Monte Carlo simulations, allowed for correcting the differences in absorbed dose between the DosiRat material (polystyrene) and the air and therefore allowed to compare DosiRat intrinsic energy response to the Birks scintillation quenching model. The energy response of DosiRat was then assessed under preclinical conditions through percentage depth dose curves (PDD) and relative output factor (ROF) measurements in water for beam diameters ranging from 1 to 25 mm. DosiRat energy response showed a coefficient of variation of 23% from 40 to 225 kV, mainly explained by the mass energy-absorption coefficient variation between polystyrene and air. A remaining variation was shown to be caused by the quenching of the scintillation and was correctly reproduced by the Birks model (with kB = 10.27 mg MeV cm). PDD and ROF measurements highlighted an energy response variation with depth and collimation up to 10%. A dose accuracy better than 1% was finally achieved with appropriate calibration and correction factors (CF), for beam collimations larger than the detector ([Formula: see text]2 mm diameter). DosiRat energy dependence was fully characterized in preclinical energy range and shown to be negligible with convenient calibration and corrections factors. It provided accurate dosimetry for medium energy (225 kV) and millimetric beams (down to 2.5 mm).

由于毫米级光束和中等 X 射线能量范围，临床前微辐照器的剂量学具有挑战性。塑料闪烁体剂量计（PSD）是此类目的的良好候选者，因为它们提供了高空间分辨率，尽管它们在低于 100keV 的能量下表现出能量依赖性。本研究旨在评估一种专用 PSD（称为 DosiRat）用于微辐照器剂量学的能量依赖性。使用 X-RAD 225Cx 辐照器，针对不同光束质量（40-225kV）测量了 PSD 相对于空气比释动能的响应。通过蒙特卡罗模拟确定的相应能谱允许校正 DosiRat 材料（聚苯乙烯）与空气之间吸收剂量的差异，从而允许比较 DosiRat 固有能量响应与 Birks 闪烁猝灭模型。然后，通过在水（光束直径从 1 到 25mm）中测量 PDD 和相对输出因子（ROF），在临床前条件下评估 DosiRat 的能量响应。DosiRat 的能量响应在 40 到 225kV 之间的变异系数为 23%，主要是由于聚苯乙烯和空气之间的质量能量吸收系数变化引起的。剩余的变化被证明是由闪烁猝灭引起的，并且被 Birks 模型（kB=10.27mg MeV cm）正确再现。PDD 和 ROF 测量突出显示了能量响应随深度和准直的变化，最大可达 10%。通过适当的校准和校正因子（CF），对于大于探测器的光束准直（[Formula: see text]2mm 直径），最终实现了剂量精度优于 1%。在临床前能量范围内充分表征了 DosiRat 的能量依赖性，并表明通过方便的校准和校正因子，其能量依赖性可以忽略不计。它为中等能量（225kV）和毫米级光束（低至 2.5mm）提供了准确的剂量学。