High dose-per-pulse electron beam dosimetry: Usability and dose-rate independence of EBT3 Gafchromic films
High dose-per-pulse electron beam dosimetry: Usability and dose-rate independence of EBT3 Gafchromic films
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DOI：
10.1002/mp.12066
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发表时间：
2017-02-01
期刊：
影响因子：
3.8
通讯作者：
Bailat, Claude
中科院分区：
文献类型：
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作者：
Jaccard, Maud;Petersson, Kristoffer;Bailat, Claude
目的：本研究的目的是评估Gafchromic EBT 3薄膜在原型高剂量/脉冲线性加速器（直线加速器）射束中用于参考剂量测量的适用性，该直线加速器能够以0.07至3000戈伊/s的平均剂量率（D-m）和高达8 x 10（6）戈伊/s的脉冲剂量率（D-p）输送电子束。要做到这一点，我们评估了EBT 3薄膜剂量测定的整体不确定性，以及能量和剂量率的依赖性，他们的respons.Material和methods：我们的剂量测定系统是由EBT 3 Gafchromic薄膜结合平板扫描仪和校准对电离室可追溯到初级标准。在EBT 3剂量测定的不确定性的所有来源进行了仔细分析，使用在临床放射治疗直线加速器的照射。通过获取和比较三种不同射束能量（4、8和12 MeV）的校准曲线，对0.25和30戈伊之间的剂量，用同一台机器研究能量依赖性。在临床直线加速器上，通过改变射束的脉冲重复频率（f）研究了D-m依赖性，以便在0.55和4.40戈伊/min之间改变D-m，而在原型机器上探测D-p依赖性，D-p范围为7 x 10（3）至8 x 10（6）戈伊/s。首先通过研究薄膜测量的剂量与感应环在机器出口处测量的电子电荷之间的相关性来确定Dp依赖性。此外，我们比较了剂量从电影独立校准的热发光剂量计（ESTA）已被报道为剂量率独立到这样高的dose-rates.Results：我们报告说，低于4%（k = 2）的不确定性可以实现在3和17戈伊之间的剂量范围。结果还表明，EBT 3膜没有显示出任何可检测的能量依赖于4和12 MeV之间的电子束能量。也没有发现D-m依赖性。此外，我们在原型直线加速器可达到的整个D-p范围内获得了薄膜和TLD之间的良好一致性，证实了在研究范围（7 x 10（3）至8 x 10（6）戈伊/s）内不存在任何剂量率依赖性。这方面的进一步证实了由薄膜测量的剂量单脉冲（D-P）和测量在原型直线加速器exit.Conclusion的每脉冲（C-P）的电荷之间的线性关系：我们的研究表明，EBT 3 Gafchromic薄膜的使用可以扩展到参考剂量测定脉冲电子束具有非常高的剂量率。测量结果的总体不确定度低于4%（k = 2），并且与剂量率和能量无关。(C)2016年美国医学物理学家协会。
Purpose: The aim of this study was to assess the suitability of Gafchromic EBT3 films for reference dose measurements in the beam of a prototype high dose-per-pulse linear accelerator (linac), capable of delivering electron beams with a mean dose-rate (D-m) ranging from 0.07 to 3000 Gy/s and a doserate in pulse (D-p) of up to 8 x 10(6) Gy/s. To do this, we evaluated the overall uncertainties in EBT3 film dosimetry as well as the energy and dose-rate dependence of their response.Material and methods: Our dosimetric system was composed of EBT3 Gafchromic films in combination with a flatbed scanner and was calibrated against an ionization chamber traceable to primary standard. All sources of uncertainties in EBT3 dosimetry were carefully analyzed using irradiations at a clinical radiotherapy linac. Energy dependence was investigated with the same machine by acquiring and comparing calibration curves for three different beam energies (4, 8 and 12 MeV), for doses between 0.25 and 30 Gy. D-m dependence was studied at the clinical linac by changing the pulse repetition frequency (f) of the beam in order to vary D-m between 0.55 and 4.40 Gy/min, while D-p dependence was probed at the prototype machine for D-p ranging from 7 x 10(3) to 8 x 10(6) Gy/s. Dp dependence was first determined by studying the correlation between the dose measured by films and the charge of electrons measured at the exit of the machine by an induction torus. Furthermore, we compared doses from the films to independently calibrated thermo-luminescent dosimeters (TLD) that have been reported as being dose-rate independent up to such high dose-rates.Results: We report that uncertainty below 4% (k = 2) can be achieved in the dose range between 3 and 17 Gy. Results also demonstrated that EBT3 films did not display any detectable energy dependence for electron beam energies between 4 and 12 MeV. No D-m dependence was found either. In addition, we obtained excellent consistency between films and TLDs over the entire D-p range attainable at the prototype linac confirming the absence of any dose-rate dependence within the investigated range (7 x 10(3) to 8 x 10(6) Gy/s). This aspect was further corroborated by the linear relationship between the dose-perpulse (D-p) measured by films and the charge per pulse (C-p) measured at the prototype linac exit.Conclusion: Our study shows that the use of EBT3 Gafchromic films can be extended to reference dosimetry in pulsed electron beams with a very high dose rate. The measurement results are associated with an overall uncertainty below 4% (k = 2) and are dose-rate and energy independent. (C) 2016 American Association of Physicists in Medicine.