Chiu-Tsao S, Massillon-Jl G, Domingo-Muñoz I, Chan M
Quality MediPhys LLC, Denville, NJ.
Instituto de Fisica, UNAM, Mexico City, MX.
Med Phys. 2012 Jun;39(6Part11):3724. doi: 10.1118/1.4735153.
To study and compare the dose response curves of the new GafChromic EBT3 film for megavoltage and kilovoltage x-ray beams, with different spatial resolution.
Two sets of EBT3 films (lot#A101711-02) were exposed to each x-ray beam (6MV, 15MV and 50kV) at 8 dose values (50-3200cGy). The megavoltage beams were calibrated per AAPM TG-51 protocol while the kilovoltage beam was calibrated following the TG-61 using an ionization chamber calibrated at NIST. Each film piece was scanned three consecutive times in the center of Epson 10000XL flatbed scanner in transmission mode, landscape orientation, 48-bit color at two separate spatial resolutions of 75 and 300 dpi. The data were analyzed using ImageJ and, for each scanned image, a region of interest (ROI) of 2×2cm at the field center was selected to obtain the mean pixel value with its standard deviation in the ROI. For each energy, dose value and spatial resolution, the average netOD and its associated uncertainty were determined. The Student's t-test was performed to evaluate the statistical differences between the netOD/dose values of the three energy modalities, with different color channels and spatial resolutions.
The dose response curves for the three energy modalities were compared in three color channels with 75 and 300dpi. Weak energy dependence was found. For doses above 100cGy, no statistical differences were observed between 6 and 15MV beams, regardless of spatial resolution. However, statistical differences were observed between 50kV and the megavoltage beams. The degree of energy dependence (from MV to 50kV) was found to be function of color channel, dose level and spatial resolution.
The dose response curves for GafChromic EBT3 films were found to be weakly dependent on the energy of the photon beams from 6MV to 50kV. The degree of energy dependence varies with color channel, dose and spatial resolution. GafChromic EBT3 films were supplied by Ashland Corp. This work was partially supported by DGAPA-UNAM grant IN102610 and Conacyt Mexico grant 127409.
研究并比较新型GafChromic EBT3薄膜针对不同空间分辨率的兆伏级和千伏级X射线束的剂量响应曲线。
两组EBT3薄膜（批次号A101711 - 02）分别以8个剂量值（50 - 3200cGy）暴露于各X射线束（6MV、15MV和50kV）下。兆伏级射线束按照AAPM TG - 51协议进行校准，而千伏级射线束按照TG - 61协议，使用在NIST校准过的电离室进行校准。每片薄膜在爱普生10000XL平板扫描仪中心以透射模式、横向、48位彩色、两种不同空间分辨率（75和300dpi）连续扫描三次。使用ImageJ对数据进行分析，对于每张扫描图像，在射野中心选取一个2×2cm的感兴趣区域（ROI），以获取该ROI内的平均像素值及其标准偏差。对于每种能量、剂量值和空间分辨率，确定平均净光密度及其相关不确定度。进行学生t检验以评估三种能量模式在不同颜色通道和空间分辨率下的净光密度/剂量值之间的统计学差异。
在75和300dpi的三种颜色通道下比较了三种能量模式的剂量响应曲线。发现能量依赖性较弱。对于高于100cGy的剂量，无论空间分辨率如何，6MV和15MV射线束之间未观察到统计学差异。然而，在50kV和兆伏级射线束之间观察到统计学差异。发现能量依赖程度（从兆伏级到50kV）是颜色通道、剂量水平和空间分辨率的函数。
发现GafChromic EBT3薄膜的剂量响应曲线对6MV至50kV光子束的能量依赖性较弱。能量依赖程度随颜色通道、剂量和空间分辨率而变化。GafChromic EBT3薄膜由亚什兰公司提供。本研究部分得到了墨西哥国立自治大学（DGAPA - UNAM）资助项目IN102610以及墨西哥国家科学技术委员会（Conacyt）资助项目127409的支持。
