Spatially fractionated ultra-high-dose-rate beams used during microbeam radiation therapy (MRT) have been shown to increase the differential response between normal and tumour tissue. Quality assurance of MRT requires a dosimeter that possesses tissue equivalence, high radiation tolerance and spatial resolution. This is currently an unsolved challenge. This work explored the use of a 500 nm thick organic semiconductor for MRT dosimetry on the Imaging and Medical Beamline at the Australian Synchrotron. Three beam filters were used to irradiate the device with peak energies of 48, 76 and 88 keV with respective dose rates of 3668, 500 and 209 Gy s⁻¹. The response of the device stabilized to 30% efficiency after an irradiation dose of 30 kGy, with a 0.5% variation at doses of 35 kGy and higher. The calibration factor after pre-irradiation was determined to be 1.02 ± 0.005 µGy per count across all three X-ray energy spectra, demonstrating the unique advantage of using tissue-equivalent materials for dosimetry. The percentage depth dose curve was within ±5% of the PTW microDiamond detector. The broad beam was fractionated into 50 microbeams (50 µm FHWM and 400 µm centre-to-centre distance). For each beam filter, the FWHMs of all 50 microbeams were measured to be 51 ± 1.4, 53 ± 1.4 and 69 ± 1.9 µm, for the highest to lowest dose rate, respectively. The variation in response suggested the photodetector possessed dose-rate dependence. However, its ability to reconstruct the microbeam profile was affected by the presence of additional dose peaks adjacent to the one generated by the X-ray microbeam. Geant4 simulations proved that the additional peaks were due to optical photons generated in the barrier film coupled to the sensitive volume. The simulations also confirmed that the amplitude of the additional peak in comparison with the microbeam decreased for spectra with lower peak energies, as observed in the experimental data. The material packaging can be optimized during fabrication by solution processing onto a flexible substrate with a non-fluorescent barrier film. With these improvements, organic photodetectors show promising prospects as a cost-effective high spatial resolution tissue-equivalent flexible dosimeter for synchrotron radiation fields.

中文翻译：

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使用有机半导体实现微束放射治疗的高空间分辨率组织等效剂量学

在微束放射治疗 (MRT) 中使用的空间分割超高剂量率束已被证明可以增加正常组织和肿瘤组织之间的差异反应。MRT 的质量保证需要具有组织等效性、高辐射耐受性和空间分辨率的剂量计。这是目前尚未解决的挑战。这项工作探索了使用 500 nm 厚的有机半导体在澳大利亚同步加速器的成像和医疗光束线上进行 MRT 剂量测定。三个光束过滤器用于以 48、76 和 88 keV 的峰值能量照射器件，剂量率分别为 3668、500 和 209 Gy s ^-1. 该装置的响应在 30 kGy 的辐射剂量后稳定在 30% 的效率，在 35 kGy 和更高的剂量下有 0.5% 的变化。在所有三个 X 射线能谱中，预辐照后的校准系数被确定为每计数 1.02 ± 0.005 µGy，证明了使用组织等效材料进行剂量测定的独特优势。百分比深度剂量曲线在 PTW microDiamond 检测器的 ±5% 以内。宽光束被分成 50 个微光束（50 µm FHWM 和 400 µm 中心到中心距离）。对于每个光束过滤器，所有 50 个微光束的 FWHM 分别测量为 51 ± 1.4、53 ± 1.4 和 69 ± 1.9 µm，分别用于最高到最低剂量率。响应的变化表明光电探测器具有剂量率依赖性。然而，Geant4模拟证明，额外的峰值是由于与敏感体积耦合的屏障膜中产生的光学光子。模拟还证实，如在实验数据中观察到的那样，对于具有较低峰值能量的光谱，与微束相比，附加峰值的幅度降低。通过在具有非荧光屏障膜的柔性基板上进行溶液处理，可以在制造过程中优化材料封装。通过这些改进，有机光电探测器显示出作为用于同步辐射场的具有成本效益的高空间分辨率组织等效柔性剂量计的广阔前景。