Correction for Ion Recombination in a Built-in Monitor Chamber of a Clinical Linear Accelerator at Ultra-High Dose Rates.
Correction for Ion Recombination in a Built-in Monitor Chamber of a Clinical Linear Accelerator at Ultra-High Dose Rates.
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DOI：
10.1667/rade-19-00012
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发表时间：
2020-12-01
影响因子：
3.4
通讯作者：
Petersson K
中科院分区：
文献类型：
--
作者：
Konradsson E;Ceberg C;Lempart M;Blad B;Bäck S;Knöös T;Petersson K
在新颖而有前途的放射疗法技术中，称为闪光灯，使用了超高剂量速率电子束。作为迈向临床试验的一步，要准确剂量递送闪光灯将需要进行剂量学进步。这项研究的目的是确定是否可以将临床线性加速器的内置变速箱用作实时剂量计，以监测超高剂量速率电子束的传递。这是通过对腔室的下水离子收集效率进行建模，并以每脉冲剂量增加的效率进行建模，从而可以考虑离子重组效应。从线性加速器中提取原始传输室信号，并以不同的剂量速率/每脉冲值的射击膜在100 cm的源至表面距离处测量其响应。在透射室上应用的偏振电压增加了2和3，提高了离子接收效率，在每脉冲值最高剂量时，相应的提高效率分别提高了一个因子1.4和2.2。使用安装在传输室数据中的逻辑函数对随着剂量渗透的增加的下水离子收集效率进行了准确的建模。将模型的性能与离子化室中离子重组的一般理论船舶模型的性能进行了比较。随后使用逻辑模型来校正从常规到超高的剂量速率的离子重组，这使得传输室可作为实时监视器，可用于临床设置中闪光电子束的剂量递送。
In the novel and promising radiotherapy technique known as FLASH, ultra-high dose-rate electron beams are used. As a step towards clinical trials, dosimetric advances will be required for accurate dose delivery of FLASH. The purpose of this study was to determine whether a built-in transmission chamber of a clinical linear accelerator can be used as a real-time dosimeter to monitor the delivery of ultra-high-dose-rate electron beams. This was done by modeling the drop-in ion-collection efficiency of the chamber with increasing dose-per-pulse values, so that the ion recombination effect could be considered. The raw transmission chamber signal was extracted from the linear accelerator and its response was measured using radio-chromic film at different dose rates/dose-per-pulse values, at a source-to-surface distance of 100 cm. An increase of the polarizing voltage, applied over the transmission chamber, by a factor of 2 and 3, improved the ion-collection efficiency, with corresponding increased efficiency at the highest dose-per-pulse values by a factor 1.4 and 2.2, respectively. The drop-in ion-collection efficiency with increasing dose-perpulse was accurately modeled using a logistic function fitted to the transmission chamber data. The performance of the model was compared to that of the general theoretical Boag models of ion recombination in ionization chambers. The logistic model was subsequently used to correct for ion recombination at dose rates ranging from conventional to ultra-high, making the transmission chamber useful as a real-time monitor for the dose delivery of FLASH electron beams in a clinical setup.