Hernández Millares Rodrigo, Mirza Jamal Ahmad, Lee Junyoung, Choi Kwon, Eom Mingi, Ye Sung-Joon
Program in Biomedical Radiation Sciences, Department of Transdisciplinary Studies, Graduate School of Convergence Science and Technology, Seoul National University, Seoul, 08826, Korea.
Isotope Production Division, Pakistan Institute of Nuclear Science and Technology, Nilore, Islamabad, 44000, Pakistan.
Med Phys. 2021 Feb;48(2):796-804. doi: 10.1002/mp.14570. Epub 2021 Jan 4.
To measure the radiosensitization by an Au-nanofilm (GNF) at a micrometer level on a radiochromic film (RCF) using confocal Raman spectroscopy (CRS).
Unlaminated radiochromic films were irradiated by 200 kVp x-ray from 0.3 to 50 Gy to obtain a calibration curve. Raman spectra of these films were measured by positioning the postirradiated RCF perpendicular to the CRS monochromatic beam and reading a depth profile of the film along the lateral axis. The Raman peak corresponding to the C ≡ C peak was obtained from a region of interest of 100 × 5 µm . To investigate the radiosensitization by GNF, two sets of RCF, one attached to a 100-nm thick GNF and the other without GNF were irradiated at 0.5 Gy by 50 and 120 kVp X-rays. The spatial resolution of the CRS on the RCF was quantified by the modulation transfer function method (MTF). Thus, in the spatial resolution determined by MTF, the doses deposited on the films were evaluated. The dose enhancement factor (DEF) was obtained in the measurable micro-size by comparing doses deposited on the RCFs with and without GNF. To verify the experimental results, Monte Carlo simulations following the experimental set up were performed using Geant4. In addition, analytical calculations for the radiosensitization by GNF were carried out.
The confocal Raman spectroscopy on the RCF achieved a spatial resolution of ~6 μm. An experimental DEF within the first 6 μm depth from the surface of RCF was found to be 17.9 for 50 kVp and 14.7 for 120 kVp. The DEF for the same depth obtained by MC and analytical calculations was 13.53 and 9.75 for 50 kVp, and 10.63 and 6.67 for 120 kVp, respectively.
The experimental DEF as a function of the distance from GNF was consistent with data from previous studies and the MC simulations, supporting that CRS in conjunction with the RCF is a feasible micrometer-resolution dosimeter.
使用共聚焦拉曼光谱（CRS）在微米水平上测量金纳米膜（GNF）对放射变色膜（RCF）的放射增敏作用。
将未层压的放射变色膜用200 kVp的X射线从0.3至50 Gy进行照射，以获得校准曲线。通过将照射后的RCF垂直于CRS单色光束定位并读取沿横轴的膜深度分布来测量这些膜的拉曼光谱。对应于C≡C峰的拉曼峰是从100×5μm的感兴趣区域获得的。为了研究GNF的放射增敏作用，两组RCF，一组附着在100 nm厚的GNF上，另一组没有GNF，分别用50和120 kVp的X射线以0.5 Gy进行照射。通过调制传递函数法（MTF）对CRS在RCF上的空间分辨率进行量化。因此，在由MTF确定的空间分辨率下，评估沉积在膜上的剂量。通过比较有和没有GNF的RCF上沉积的剂量，在可测量的微观尺寸上获得剂量增强因子（DEF）。为了验证实验结果，使用Geant4按照实验设置进行蒙特卡罗模拟。此外，还对GNF的放射增敏作用进行了解析计算。
RCF上的共聚焦拉曼光谱实现了约6μm的空间分辨率。发现在距RCF表面6μm深度内，50 kVp时的实验DEF为17.9，120 kVp时为14.7。通过蒙特卡罗模拟和解析计算在相同深度下获得的50 kVp时的DEF分别为13.53和9.75，120 kVp时分别为10.63和6.67。
作为距GNF距离函数的实验DEF与先前研究的数据和蒙特卡罗模拟结果一致，支持CRS与RCF结合是一种可行的微米分辨率剂量计。
