Guan Fada, Wang Xiaochun, Yang Ming, Draeger Emily, Han Dae, Iga Kiminori, Guo Fanqing, Perles Luis, Li Yuting, Sahoo Narayan, Mohan Radhe, Chen Zhe
Department of Radiation Physics, The University of Texas MD Anderson Cancer Center,1515 Holcombe Boulevard, Houston, Texas 77030, USA.
Department of Therapeutic Radiology, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06510, USA; Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, Texas 77030.
Precis Radiat Oncol. 2023 Mar;7(1):15-26. doi: 10.1002/pro6.1187. Epub 2023 Mar 2.
EBT-XD model of Gafchromic films has a broader optimal dynamic dose range, up to 40 Gy, compared to its predecessor models. This characteristic has made EBT-XD films suitable for high-dose applications such as stereotactic body radiotherapy and stereotactic radiosurgery, as well as ultra-high dose rate FLASH radiotherapy. The purpose of the current study was to characterize the dependence of EBT-XD film response on linear energy transfer (LET) and dose rate of therapeutic protons from a synchrotron. A clinical spot-scanning proton beam was used to study LET dependence at three dose-averaged LET (LET) values of 1.0 keV/µm, 3.6 keV/µm, and 7.6 keV/µm. A research proton beamline was used to study dose rate dependence at 150 Gy/second in the FLASH mode and 0.3 Gy/second in the non-FLASH mode. Film response data from LET values of 0.9 keV/µm and 9.0 keV/µm of the proton FLASH beam were also compared. Film response data from a clinical 6 MV photon beam were used as a reference. Both gray value method and optical density (OD) method were used in film calibration. Calibration results using a specific OD calculation method and a generic OD calculation method were compared. The four-parameter NIH Rodbard function and three-parameter rational function were compared in fitting the calibration curves. Experimental results showed that the response of EBT-XD film is proton LET dependent but independent of dose rate. Goodness-of-fit analysis showed that using the NIH Rodbard function is superior for both protons and photons. Using the "specific OD + NIH Rodbard function" method for EBT-XD film calibration is recommended.
与前代型号相比，Gafchromic 薄膜的 EBT-XD 型号具有更宽的最佳动态剂量范围，高达 40 Gy。这一特性使 EBT-XD 薄膜适用于高剂量应用，如立体定向体部放射治疗和立体定向放射外科手术，以及超高剂量率的 FLASH 放射治疗。本研究的目的是表征 EBT-XD 薄膜响应与来自同步加速器的治疗质子的线能量转移 (LET) 和剂量率之间的关系。使用临床点扫描质子束研究了在 1.0 keV/µm、3.6 keV/µm 和 7.6 keV/µm 这三个剂量平均 LET 值下的 LET 依赖性。使用研究质子束线研究了在 FLASH 模式下 150 Gy/秒和非 FLASH 模式下 0.3 Gy/秒的剂量率依赖性。还比较了质子 FLASH 束 LET 值为 0.9 keV/µm 和 9.0 keV/µm 时的薄膜响应数据。来自临床 6 MV 光子束的薄膜响应数据用作参考。薄膜校准中同时使用了灰度值法和光密度 (OD) 法。比较了使用特定 OD 计算方法和通用 OD 计算方法的校准结果。在拟合校准曲线时比较了四参数 NIH Rodbard 函数和三参数有理函数。实验结果表明，EBT-XD 薄膜的响应与质子 LET 有关，但与剂量率无关。拟合优度分析表明，对于质子和光子，使用 NIH Rodbard 函数都更具优势。建议使用“特定 OD + NIH Rodbard 函数”方法对 EBT-XD 薄膜进行校准。
