Exradin A30平行板电离室作为超高中子剂量率（UHDR）电子束参考剂量计的评估
Evaluation of the Exradin A30 Parallel Plate Ion Chamber as a Reference Dosimeter in Ultra-High Dose Rate (UHDR) Electron Beams
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中文总结 AI 辅助
本研究评估Exradin A30平行板电离室作为超高中子剂量率电子束参考剂量计的性能，明确其漏电流、电荷收集效率等参数特性，证实经修正后该电离室可用于UHDR电子束参考剂量测定。
中文摘要 AI 辅助
超高中子剂量率（UHDR）束流（>40 Gy/s）的可靠参考剂量测定颇具挑战，因为传统电离室（IC）会因离子复合出现饱和现象。Exradin A30电离室采用超薄0.3 mm电极间距以提升电荷收集效率（CCE）。本研究通过表征漏电流、电荷收集效率（CCE）、极性修正（Ppol）及束流品质修正因子（kQ），评估商用A30电离室作为UHDR电子束参考剂量计的性能。实验使用9 MeV IntraOp Mobetron加速器产生的电子束，最大每脉冲剂量（DPP）达9 Gy，瞬时剂量率为2.25 MGy/s。在接地水等效塑料、蒸馏水及盐水中开展测量，通过在固定4 μs脉冲宽度下改变源皮距（SSD）调整DPP，脉冲重复频率（PRF）范围为5至90 Hz。在匹配的UHDR与常规剂量、能量条件下，使用EBT-XD胶片测定CCE；同时在蒸馏水和盐水中评估CCE与Ppol随DPP、PRF的变化；通过蒙特卡罗模拟计算kQ值，并在TrueBeam电子束中测量kQ值。实验测得漏电流<2 fA；CCE与Ppol均随DPP升高而降低，但三种模体中CCE始终保持在90%-99%，Ppol在液态水和固体水中从0.990降至0.981；在5-90 Hz范围内，CCE和Ppol均不依赖于PRF。除9 MeV时测量与计算的kQ值相差2%外，其余能量下二者偏差在0.8%以内。A30在蒸馏水和盐水中，当DPP达5 Gy时复合率为5%；其在固体模体中的响应受电荷积累影响，接地可缓解该问题。通过适当的CCE修正和使用接地固体模体，商用A30电离室适用于UHDR电子束的参考剂量测定。
英文摘要
Reliable reference dosimetry for ultra-high dose-rate (UHDR) beams (>40 Gy/s) is challenging because conventional ionization chambers (ICs) exhibit saturation from ion recombination. The Exradin A30 IC uses an ultra-thin 0.3-mm electrode spacing to improve charge-collection efficiency (CCE). This study evaluated the commercial A30 as a reference dosimeter for UHDR electron beams by characterizing leakage current, CCE, polarity correction (Ppol), and beam-quality correction factors (kQ). Measurements were performed with a 9-MeV IntraOp Mobetron from the accelerator head, achieving up to 9 Gy per pulse (DPP) and an instantaneous dose rate of 2.25 MGy/s. Data were acquired in grounded water-equivalent plastic, distilled water, and saline water. DPP was varied by changing SSD at a fixed 4-μs pulse width, while pulse repetition frequency (PRF) ranged from 5 to 90 Hz. CCE was determined using EBT-XD film under matched UHDR and conventional dose and energy conditions. CCE and Ppol were also evaluated as functions of DPP and PRF in distilled and saline water. Values of kQ were calculated using Monte Carlo simulations and measured in TrueBeam electron beams. Leakage current was <2 fA. Both CCE and Ppol decreased with increasing DPP; however, CCE remained 90-99% across all three phantoms, while Ppol decreased from 0.990 to 0.981 in liquid and solid water. Neither CCE nor Ppol depended on PRF over 5-90 Hz. Measured and calculated kQ values agreed within 0.8% at all energies except 9 MeV, where they differed by 2%. The A30 exhibited 5% recombination at DPP up to 5 Gy in distilled and saline water. Its response in solid phantoms was affected by charge buildup, which was mitigated by grounding. With appropriate CCE corrections and grounded solid phantoms, the commercial A30 is suitable for reference dosimetry in UHDR electron beams.
