Methods of improving the accuracy of high-energy X-ray absorbed dose calculated using a convolution approach

使用直线加速器产生4、10和15 mv x射线的三重能量束。进行了以下实验和理论研究。在x射线强度透射数据的基础上，提出了一种估算x射线光谱的方法，并构建了计算程序。在这种情况下，使用楔形和补偿器引起的初级x射线光谱变化可以很容易地准确评估，并且可以很容易地准确评估辐照体内的初级x射线光谱变化，因此可以进行更准确的剂量计算。在x射线谱的基础上，将水中衰减系数表示为深度的函数，进而推导出零面积最大组织比（TIR）。利用零面积TMR公式中的一些常数来构造初级和散射剂量扩散函数。采用水和三层co - rk模型测量了几种辐照场的组织幻像比（tpr）。在几个辐照场中，还使用水和3层软木模型测量了剂量ocr（偏离中心比）。这些数据集被用来重新确认这些基本函数，用于使用卷积方法进行剂量计算，如初级剂量扩散函数、散射-剂量扩散函数、污染物电子强度函数和准直器OCR函数。引入了“准直器OCR”的概念，用于评价一对上下颚的屏蔽效果。本文还引入了“源OCR”的概念，用于评价无限场入射x射线的强度。提出了有限场中一点处的入射x射线强度用准直OCR和源OCR函数的乘积表示。提出了一种将多叶准直器（MLC）、楔形、屏蔽块和沙发作为受辐照体的组成部分的剂量计算方法。利用初值和散点剂量扩散函数表达式可以解析整合的特点，试图加快三维剂量计算软件的速度。少

Using a linear accelerator producing triplet-energy beams of 4-, 10-, and 15-MV X-rays. the following experimental and theoretical studies were performed.1.On the basis of X-ray intensity transmission data, we developed a method to estimate X-ray spectra and then constructed its calculation program. Under this situation, the primary X-ray spectrum variation caused by using wedges and compensators can be easily evaluated with accuracy and the primary X-ray spectrum variation within an irradiated body can also be easily evaluated with accuracy : Therefore, more accurate dose calculations can now be performed.2.On the basis of the X-ray spectrum, the in-water attenuation coefficient was expressed as a function of depth, and then the zero-area tissue-maximum ratio (TIR) was formulated. Some of the constants in the zero-area TMR formulation were utilized for constructing primary and scatter dose spread functions.3.Sets of tissue-phantom ratios (TPRs) were measured using water and 3-layed co … More rk phantoms for several irradiation fields. Sets of dose OCRs (off-center ratios) were also measured using water and 3-layed cork phantoms for several irradiation fields. These sets of data were utilized to reconfirm such fundamental functions, for dose calculation using a convolution method, as primary-dose spread functions, scatter-dose spread functions, contaminant electron intensity functions, and collimator OCR functions.4.The concept of "collimator OCR" was introduced for evaluation of the shielding effect due to a pair of lower and upper jaws. The concept of "source OCR" was also introduced for evaluation of the incident X-ray intensity at an infinite field. It was proposed that the incident X-ray intensity at a point for a finite field was expressed as the product of the collimator OCR and source OCR functions.5.A dose calculation approach was proposed to regard the multi-leaf collimator (MLC), the wedge, the shielding blocks, and the couch as parts of an irradiated body.6.Speeding Up of the 3D dose calculation soft was attempted by utilizing the fact that both primary and scatter dose spread functional expressions could be integrated analytically. Less