Posar Jessie A, Davis Jeremy, Brace Owen, Sellin Paul, Griffith Matthew J, Dhez Olivier, Wilkinson Dean, Lerch Michael L F, Rosenfeld Anatoly, Petasecca Marco
Centre for Medical Radiation Physics, University of Wollongong, NSW 2522, Australia.
Department of Physics, University of Surrey, Guildford GU2 7XH, United Kingdom.
Phys Imaging Radiat Oncol. 2020 Jun 5;14:48-52. doi: 10.1016/j.phro.2020.05.007. eCollection 2020 Apr.
Measurement of dose delivery is essential to guarantee the safety of patients undergoing medical radiation imaging or treatment procedures. This study aimed to evaluate the ability of organic semiconductors, coupled with a plastic scintillator, to measure photon dose in clinically relevant conditions, and establish its radiation hardness. Thereby, proving organic devices are capable of being a water-equivalent, mechanically flexible, real-time dosimeter.
The shelf-life of an organic photodiode was analyzed to 40 kGy by comparison of the charge-collection-efficiency of a 520 nm light emitting diode. A non-irradiated and pre-irradiated photodiode was coupled to a plastic scintillator and their response to 6 MV photons was investigated. The dose linearity, dose-per-pulse dependence and energy dependence was characterized. Finally, the percentage depth dose (PDD) between 0.5 and 20 cm was compared with ionization chamber measurements.
Sensitivity to 6 MV photons was (190 ± 0.28) pC/cGy and (170 ± 0.11) pC/cGy for the non-irradiated and pre-irradiated photodiode biased at -2 V. The response was independent of the dose-per-pulse between 0.031 and 0.34 mGy/pulse. An energy dependence was found for low keV energies, explained by the energy dependence of the scintillator which plateaued between 70 keV and 1.2 MeV. The PDD was within ±3% of the ionization chamber.
Coupling an organic photodiode with a plastic scintillator provided reliable measurement of a range of photon energies. Dose-per-pulse and energy independence advocate their use as a dosimeter, specifically image-guided treatment without beam-quality correction factors. Degradation effects of organic semiconducting materials deteriorate sensor response but can be stabilized.
剂量输送测量对于确保接受医学放射成像或治疗程序的患者安全至关重要。本研究旨在评估有机半导体与塑料闪烁体相结合在临床相关条件下测量光子剂量的能力，并确定其辐射硬度。从而证明有机器件能够成为一种水等效、机械灵活的实时剂量计。
通过比较520 nm发光二极管的电荷收集效率，分析有机光电二极管在40 kGy剂量下的保质期。将未辐照和预辐照的光电二极管与塑料闪烁体耦合，并研究它们对6 MV光子的响应。对剂量线性、每脉冲剂量依赖性和能量依赖性进行了表征。最后，将0.5至20 cm之间的百分深度剂量（PDD）与电离室测量结果进行比较。
对于偏置在-2 V的未辐照和预辐照光电二极管，对6 MV光子的灵敏度分别为(190±0.28) pC/cGy和(170±0.11) pC/cGy。响应与每脉冲剂量在0.031至0.34 mGy/脉冲之间无关。发现低keV能量存在能量依赖性，这可以通过闪烁体在70 keV至1.2 MeV之间达到平稳的能量依赖性来解释。PDD在电离室的±3%范围内。
将有机光电二极管与塑料闪烁体耦合可对一系列光子能量进行可靠测量。每脉冲剂量和能量独立性支持将其用作剂量计，特别是在无需束流质量校正因子的图像引导治疗中。有机半导体材料的降解效应会使传感器响应变差，但可以使其稳定。
