高分辨率半导体矩阵的剂量学特性

Dosimetric characteristics of a high-resolution semiconductor matrix

目的:研究一种新的高分辨率探测器矩阵的临床剂量学特性。方法:使用泛野校准法,在直线加速器6 MV光子线下对矩阵进行一致性校准。测量矩阵的短期和长期稳定性、剂量线性、剂量率响应、射野大小依赖性,并与电离室的测量结果进行比较。测量相应能量下矩阵的表面等效厚度,测量射野离轴比曲线并且与三维水箱测量结果进行了比较。设计一组条形野,以及一组由不同大小方野形成的组合野,使用探测器矩阵和Mapcheck进行测量,并与治疗计划系统计算结果进行比较。结果:归一后矩阵的短期重复性标准偏差为0.075%,最大偏差为0.14%;长期重复性标准偏差为0.69%,最大偏差为0.92%。剂量线性经直线回归后的R2=1.0000;在40~600 MU/min剂量率范围内矩阵中心探头变化范围为0.62%;与指形电离室相比,在25 cm方野时射野输出因子偏差为1.2%,3 cm方野时为4.4%。在10 cm深度处校准时矩阵测量的离轴比曲线与三维水箱测量结果相对吻合,误差在2%以内;矩阵的表面等效厚度约为0.4~0.5 cm;在3%/3 mm和2%/2 mm标准下,Super Matrix和Mapcheck测量方野组合野计划的γ通过率分别为100.0%、98.8%和99.6%、97.5%。测量MLC条形野计划的γ通过率分别为99.1%、94.4%和99.4%、94.4%。结论:Super Matrix具有良好的剂量学特性,满足临床质量控制的基本要求。

Objective To investigate the clinical dosimetric characteristics of a novel high-resolution detector matrix,Super Matrix.Methods The consistency calibration for the matrix was carried out under the 6 MV photon beam of linear accelerator using flood-field calibration method.The properties of the matrix including short-term and long-term stabilities,dose linearity,response at different dose rates and field size dependence were measured,and then the measurement results were compared with those obtained by ionization chamber.The surface equivalent thickness of the matrix was measured under the corresponding energy,and the off-axis ratio curve of the field was measured and then compared with the measurement results of three-dimensional water tank.A set of strip fields and a group of combined field which was composed of square fields of different sizes were designed,and the measurement results obtained by detector matrix and Mapcheck were compared with TPS calculation value.Results After normalization,the standard deviations of the short-term and long-term repeatabilities of the matrix were 0.075%and 0.69%,with the maximum deviation of 0.14%and 0.92%,respectively.The dose linearity R2=1.0000 after linear regression.The deviation of the probe at the center of the matrix was 0.62%in the dose rate range of 40 to 600 MU/min.Compared with the results obtained by thimble ionization chamber,the deviation of output factor was 1.2%in 25 cm square field and 4.4%in 3 cm square field.The off-axis ratio curve of the matrix measurements was closely matched the measurement results of three-dimensional water tank,when the matrix was calibrated at the depth of 10cm,and the deviation was within 2%.The surface equivalent thickness of the matrix was about 0.4 to 0.5 cm.Under the standards of 3%/3mm and 2%/2 mm,the gamma passing rates of combined field plans based on Super Matrix and Mapcheck measurements were 100.0%,98.8%,and 99.6%,97.5%,respectively,and the gamma passing rates of MLC strip field plans were 99.1%,94.4%,and 99.4%,94.4%,respectively.Conclusion Super Matrix has good dosimetric characteristics to meet the basic requirements of clinical quality control.