低密度剂量矩阵转换为高密度剂量矩阵的算法  

Converting low density 2D array dose distributions to high density 2D array ones

作　　者：程秀艳[1] 李明辉 胡逸民 

机构地区：[1]武汉大学物理科学与技术学院,湖北武汉430072 [2]中国医学科学院/北京协和医科大学肿瘤医院放射治疗中心,北京100021

出　　处：《中国医学物理学杂志》2015年第3期397-400,共4页Chinese Journal of Medical Physics

摘　　要：目的:建立一种插值算法,在用胶片采样得到的低密度剂量矩阵各采样点之间插值,使采样得到的低密度剂量分布矩阵转换为高密度剂量分布矩阵,然后与胶片采样的高密度剂量矩阵进行比较。方法:(1)绘制胶片的光密度-剂量特性曲线将光密度值转化为剂量值;(2)与EPID相同位置处,在用胶片得到的剂量分布矩阵上采样得到一个大小为840×840的高密度原矩阵,再在原矩阵上每隔6个点取一个值,得到一个大小为120×120的低密度矩阵,此方法是仿照Mapcheck2空间分辨率为7 mm,要将其插值为1 mm而进行;(3)对此大小为120×120的二维低密度矩阵,采用双立方插值算法,将其插值回大小为840×840的新矩阵;(4)将两个大小同为840×840的原矩阵与新矩阵的对应点进行3%和5%的剂量偏差的比较;(5)在相同的EPID位置处用Mapcheck2得到相同条件下的剂量分布,对此剂量分布采用上述双立方插值的方法进行间隔1 mm插值,将此插值后的剂量分布与胶片得到的剂量分布进行3 mm 3%标准Gamma分析。结果:对两个大小同为840×840矩阵的对应点的剂量偏差的比较中,射野80%宽度范围内有94.59%的点剂量偏差都在3%以内,有99.32%的点剂量偏差都在5%以内;对用Mapcheck2插值后的剂量分布与胶片得到的剂量分布的比较中,其3 mm 3%标准Gamma分析的通过率为92.28%。结论:采用双立方插值算法可以使低密度剂量分布矩阵转换为类似于胶片的高密度剂量分布矩阵,且结果具有可靠性。Objective To convert low density 2D array dose distributions to high density 2D array ones by establishing an interpolation algorithm, interpolating between the sampling points of low density 2D array dose distributions based on film dosimetry, and to compare it with the high density 2D array from the film. Methods The curve of optical density of the film and dosimetry characteristics converted the optical density to dose values. At the same EPID position, an exposed film by 6 MV X-rays was sampled out a high density 2D matrix with a resolution of 840~ 840 and then a dose matrix with resolution of 120~ 120 was sampled out as a new low density 2D array dose matrix by taking the value at every six points in the original matrix. This method was designed by simulating Mapcheck2 that spatial resolution was 7 mm and that interpolation was 1 mm. And the low density 2D array dose matrix with resolution of 120~ 120 was converted to a new virtual high density 2D array dose matrix with resolution of 840 ~ 840 by a bicubic interpolation algorithm. The dose comparisons among the corresponding dose points between the original and the virtual high density 2D dose array distributions were carried out with 3% and 5% dose deviation. At the same EPID position, a dose distribution with the same conditions was developed by the mapcheck2. The dose distribution was interpolated to a new one with 1 mm spatial resolution by the bicubic interpolation algorithm. And then the dose distribution was compared with the one from the film by the Gamma analysis, under the 3 mm 3% standards. Results The comparison results between the two 840×840 2D array dose matrix showed that in the 80%-wideof the field, the deviations of 94.59%of all points was within 3%, and 99.32% of all points was within 5%. In the comparison of the dose distribution between the Mapeheck2 and the film, the pass rate was 92.28% by the standard Gamma analysis. Conclusion The bicubic interpolation algorithm can successfully convert a low density dose matrix to a higher one, sim

关 键 词：双立方插值 低密度剂量分布 高密度剂量分布 

分 类 号：R815[医药卫生—放射医学]