Boivin Jonathan, Beddar Sam, Bonde Chris, Schmidt Daniel, Culberson Wesley, Guillemette Maxime, Beaulieu Luc
Département de Physique, de Génie physique et d'Optique, et Centre de recherche sur le cancer, Université Laval, Québec, QC G1V 0A6, Canada. Département de Radio-Oncologie et Axe oncologie du Centre de recherche du CHU de Québec, CHU de Québec-Université Laval, Québec, QC G1R 2J6, Canada.
Phys Med Biol. 2016 Aug 7;61(15):5569-86. doi: 10.1088/0031-9155/61/15/5569. Epub 2016 Jul 6.
To characterize the low energy behavior of scintillating materials used in plastic scintillation detectors (PSDs), 3 PSDs were developed using polystyrene-based scintillating materials emitting in different wavelengths. These detectors were exposed to National Institute of Standards and Technology (NIST)-matched low-energy beams ranging from 20 kVp to 250 kVp, and to (137)Cs and (60)Co beams. The dose in polystyrene was compared to the dose in air measured by NIST-calibrated ionization chambers at the same location. Analysis of every beam quality spectrum was used to extract the beam parameters and the effective mass energy-absorption coefficient. Monte Carlo simulations were also performed to calculate the energy absorbed in the scintillators' volume. The scintillators' expected response was then compared to the experimental measurements and an energy-dependent correction factor was identified to account for low-energy quenching in the scintillators. The empirical Birks model was then compared to these values to verify its validity for low-energy electrons. The clear optical fiber response was below 0.2% of the scintillator's light for x-ray beams, indicating that a negligible amount of fluorescence contamination was produced. However, for higher-energy beams ((137)Cs and (60)Co), the scintillators' response was corrected for the Cerenkov stem effect. The scintillators' response increased by a factor of approximately 4 from a 20 kVp to a (60)Co beam. The decrease in sensitivity from ionization quenching reached a local minimum of about [Formula: see text] between 40 keV and 60 keV x-ray beam mean energy, but dropped by 20% for very low-energy (13 keV) beams. The Birks model may be used to fit the experimental data, but it must take into account the energy dependence of the kB quenching parameter. A detailed comprehension of intrinsic scintillator response is essential for proper calibration of PSD dosimeters for radiology.
为了表征塑料闪烁探测器（PSD）中使用的闪烁材料的低能行为，使用发射不同波长光的聚苯乙烯基闪烁材料开发了3个PSD。这些探测器被暴露于美国国家标准与技术研究院（NIST）匹配的20 kVp至250 kVp的低能束，以及（137）Cs和（60）Co束。将聚苯乙烯中的剂量与在同一位置由NIST校准的电离室测量的空气中的剂量进行比较。对每个束质量谱进行分析以提取束参数和有效质量能量吸收系数。还进行了蒙特卡罗模拟以计算闪烁体体积中吸收的能量。然后将闪烁体的预期响应与实验测量值进行比较，并确定一个能量相关的校正因子以考虑闪烁体中的低能猝灭。然后将经验性的伯克斯模型与这些值进行比较，以验证其对低能电子的有效性。对于X射线束，透明光纤响应低于闪烁体光的0.2%，表明产生的荧光污染量可忽略不计。然而，对于更高能量的束（（137）Cs和（60）Co），对闪烁体的响应进行了切伦科夫尾效校正。从20 kVp到（60）Co束，闪烁体的响应增加了约4倍。电离猝灭导致的灵敏度下降在40 keV至60 keV X射线束平均能量之间达到约[公式：见原文]的局部最小值，但对于非常低能量（13 keV）的束下降了20%。伯克斯模型可用于拟合实验数据，但必须考虑kB猝灭参数的能量依赖性。对于放射学中PSD剂量计的正确校准，对本征闪烁体响应的详细理解至关重要。
