Development of an ultra-thin parallel plate ionization chamber for dosimetry in FLASH radiotherapy.
Development of an ultra-thin parallel plate ionization chamber for dosimetry in FLASH radiotherapy.
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开发用于闪光放射疗法中剂量法的超薄平行板电离室的开发。
DOI：
10.1002/mp.15668
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发表时间：
2022-07
期刊：
影响因子：
3.8
通讯作者：
Paz-Martin, Jose
中科院分区：
文献类型：
--
作者：
Gomez, Faustino;Gonzalez-Castano, Diego M.;Gomez Fernandez, Nicolas;Pardo-Montero, Juan;Schueller, Andreas;Gasparini, Alessia;Vanreusel, Verdi;Verellen, Dirk;Felici, Giuseppe;Kranzer, Rafael;Paz-Martin, Jose
常规空气电离室(IC)的离子复合校正因子在每脉冲剂量比常规放射治疗中使用的剂量高的情况下显著偏离单位。这一事实使这些设备不适合用于闪光和放射治疗的超高剂量/脉冲射线的剂量学表征。我们介绍了一种超薄平行板IC的设计、开发和表征，该IC可用于超高剂量率(UHDR)传输，并具有最小的复合。通过数值求解电离辐射载流子输运的耦合微分方程组，模拟了平行板IC的电荷收集效率(CCE)。在此基础上，找出了最佳参数，以设计出一种线性响应的集成电路，在4个S脉冲宽度下，每个脉冲的剂量(偏差小于1%)可达10Gy.作为概念验证，搭建了两个排气平行板IC样机，并在不同的超高脉冲剂量率电子束中进行了测试。已经发现，通过将电极间距减小到0.25 mm，可以将平行板IC的剂量率工作范围扩展到在临床级静电计的标准电压下的超高剂量/脉冲范围，很好地扩展到几个GY/脉冲。这两个IC原型都表现出了数值模拟所预测的行为。其中一种所谓的超薄平行板电离室(UTIC)样机能够测量高达10Gy/脉冲、4 S脉冲持续时间，在300V下工作，在不确定度(电子闪光直线加速器，SIT)内没有明显偏离线性度。另一台样机在250V电压下工作，脉宽2.5Gy2.5 S，CCE大于98.6%(位于德国联邦理工学院的计量电子加速器)。这项工作展示了通过减小电极之间的间距，将IC的剂量率工作范围扩展到超高剂量/脉冲范围的能力。结果表明，UTIC适用于UHDR电子束的测量。
Conventional air ionization chambers (ICs) exhibit ion recombination correction factors that deviate substantially from unity when irradiated with dose per pulse magnitudes higher than those used in conventional radiotherapy. This fact makes these devices unsuitable for the dosimetric characterization of beams in ultra‐high dose per pulse as used for FLASH radiotherapy. We present the design, development, and characterization of an ultra‐thin parallel plate IC that can be used in ultra‐high dose rate (UHDR) deliveries with minimal recombination. The charge collection efficiency (CCE) of parallel plate ICs was modeled through a numerical solution of the coupled differential equations governing the transport of charged carriers produced by ionizing radiation. It was used to find out the optimal parameters for the purpose of designing an IC capable of exhibiting a linear response with dose (deviation less than 1%) up to 10 Gy per pulse at 4 s pulse duration. As a proof of concept, two vented parallel plate IC prototypes have been built and tested in different ultra‐high pulse dose rate electron beams. It has been found that by reducing the distance between electrodes to a value of 0.25 mm it is possible to extend the dose rate operating range of parallel plate ICs to ultra‐high dose per pulse range, at standard voltage of clinical grade electrometers, well into several Gy per pulse. The two IC prototypes exhibit behavior as predicted by the numerical simulation. One of the so‐called ultra‐thin parallel plate ionization chamber (UTIC) prototypes was able to measure up to 10 Gy per pulse, 4 s pulse duration, operated at 300 V with no significant deviation from linearity within the uncertainties (ElectronFlash Linac, SIT). The other prototype was tested up to 5.4 Gy per pulse, 2.5 s pulse duration, operated at 250 V with CCE higher than 98.6% (Metrological Electron Accelerator Facility, MELAF at Physikalisch‐Technische Bundesanstalt, PTB). This work demonstrates the ability to extend the dose rate operating range of ICs to ultra‐high dose per pulse range by reducing the spacing between electrodes. The results show that UTICs are suitable for measurement in UHDR electron beams.
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