Di Lillo F, Mettivier G, Sarno A, Tromba G, Tomic N, Devic S, Russo P
Dipartimento di Fisica "Ettore Pancini," Università di Napoli Federico II and INFN Sezione di Napoli, Via Cintia, Napoli I-80126, Italy.
Elettra-Sincrotrone Trieste SCpA, Strada Statale S.S. 14 km 163.5, Basovizza, Trieste I-34012, Italy.
Med Phys. 2016 Jan;43(1):583. doi: 10.1118/1.4939063.
This work investigates the energy response and dose-response curve determinations for XR-QA2 radiochromic film dosimetry system used for synchrotron radiation work and for quality assurance in diagnostic radiology, in the range of effective energies 18-46.5 keV.
Pieces of XR-QA2 films were irradiated, in a plane transverse to the beam axis, with a monochromatic beam of energy in the range 18-40 keV at the ELETTRA synchrotron radiation facility (Trieste, Italy) and with a polychromatic beam from a laboratory x-ray tube operated at 80, 100, and 120 kV. The film calibration curve was expressed as air kerma (measured free-in-air with an ionization chamber) versus the net optical reflectance change (netΔR) derived from the red channel of the RGB scanned film image. Four functional relationships (rational, linear exponential, power, and logarithm) were tested to evaluate the best curve for fitting the calibration data. The adequacy of the various fitting functions was tested by using the uncertainty analysis and by assessing the average of the absolute air kerma error calculated as the difference between calculated and delivered air kerma. The sensitivity of the film was evaluated as the ratio of the change in net reflectance to the corresponding air kerma.
The sensitivity of XR-QA2 films increased in the energy range 18-39 keV, with a maximum variation of about 170%, and decreased in the energy range 38-46.5 keV. The present results confirmed and extended previous findings by this and other groups, as regards the dose response of the radiochromic film XR-QA2 to monochromatic and polychromatic x-ray beams, respectively.
The XR-QA2 radiochromic film response showed a strong dependence on beam energy for both monochromatic and polychromatic beams in the range of half value layer values from 0.55 to 6.1 mm Al and corresponding effective energies from 18 to 46.5 keV. In this range, the film response varied by 170%, from a minimum sensitivity of 0.0127 to a maximum sensitivity of 0.0219 at 10 mGy air kerma in air. The more suitable function for air kerma calibration of the XR-QA2 radiochromic film was the power function. A significant batch-to-batch variation, up to 55%, in film response at 120 kV (46.5 keV effective energy) was observed in comparison with published data.
本研究调查用于同步加速器辐射工作及诊断放射学质量保证的XR-QA2放射变色薄膜剂量测定系统在18 - 46.5 keV有效能量范围内的能量响应和剂量响应曲线测定。
在意大利的里雅斯特的ELETTRA同步加速器辐射设施中，用能量范围为18 - 40 keV的单色光束，以及来自工作在80、100和120 kV的实验室X射线管的多色光束，在垂直于束轴的平面内照射XR-QA2薄膜片。薄膜校准曲线表示为空气比释动能（用电离室在空气中自由测量）与从RGB扫描薄膜图像的红色通道得出的净光学反射率变化（净ΔR）的关系。测试了四种函数关系（有理函数、线性指数函数、幂函数和对数函数），以评估拟合校准数据的最佳曲线。通过使用不确定度分析以及评估计算得出的空气比释动能与传递的空气比释动能之差计算得到的绝对空气比释动能误差的平均值，来测试各种拟合函数的适用性。薄膜的灵敏度评估为净反射率变化与相应空气比释动能的比值。
XR-QA2薄膜的灵敏度在18 - 39 keV能量范围内增加，最大变化约为170%，在38 - 46.5 keV能量范围内降低。就放射变色薄膜XR-QA2分别对单色和多色X射线束的剂量响应而言，本研究结果证实并扩展了本研究小组及其他小组先前的发现。
在半值层值从0.55到6.1 mm Al以及相应有效能量从18到46.5 keV的范围内，对于单色光束和多色光束，XR-QA2放射变色薄膜的响应都显示出对束能量的强烈依赖性。在此范围内，薄膜响应变化了170%，在空气中10 mGy空气比释动能时，灵敏度从最小值0.0127变化到最大值0.0219。对XR-QA2放射变色薄膜进行空气比释动能校准的更合适函数是幂函数。与已发表数据相比，观察到在120 kV（有效能量46.5 keV）时薄膜响应存在高达55%的显著批次间差异。
