Vijayan Sarath, Rana Vijay K, Rudin Stephen, Bednarek Daniel R
Toshiba Stroke and Vascular Research Center, University at Buffalo, Buffalo, NY 14214.
Proc SPIE Int Soc Opt Eng. 2015 Mar 18;9412:94122I. doi: 10.1117/12.2082292.
The skin dose tracking system (DTS) that we developed provides a color-coded illustration of the cumulative skin dose distribution on a 3D graphic of the patient during fluoroscopic procedures for immediate feedback to the interventionist. To improve the accuracy of dose calculation, we now have incorporated two additional important corrections (1) for the holder used to immobilize the head in neuro-interventions and (2) for the built-in compensation filters used for beam equalization. Both devices have been modeled in the DTS software so that beam intensity corrections can be made. The head-holder is modeled as two concentric hemi-cylindrical surfaces such that the path length between those surfaces can be determined for rays to individual points on the skin surface. The head-holder on the imaging system we used was measured to attenuate the primary x-rays by 10 to 20% for normal incidence, and up to 40% at non-normal incidence. In addition, three compensation filters of different shape are built into the collimator apparatus and were measured to have attenuation factors ranging from 58% to 99%, depending on kVp and beam filtration. These filters can translate and rotate in the beam and their motion is tracked by the DTS using the digital signal from the imaging system. When it is determined that a ray to a given point on the skin passes through the compensation filter, the appropriate attenuation correction is applied. These corrections have been successfully incorporated in the DTS software to provide a more accurate determination of skin dose.
我们开发的皮肤剂量跟踪系统（DTS）可在透视检查过程中，在患者的三维图形上提供累积皮肤剂量分布的彩色编码图示，以便立即向介入医生提供反馈。为提高剂量计算的准确性，我们现在纳入了两项重要的额外校正：（1）针对神经介入中用于固定头部的固定器；（2）针对用于束流均衡的内置补偿滤波器。这两种设备均已在DTS软件中建模，以便进行束流强度校正。头部固定器建模为两个同心半圆柱面，这样就可以确定这些表面之间的路径长度，以计算射向皮肤表面各点的射线的路径长度。我们使用的成像系统上的头部固定器经测量，对于垂直入射，可使初级X射线衰减10%至20%，对于非垂直入射，衰减可达40%。此外，准直器装置中内置了三种不同形状的补偿滤波器，经测量，其衰减因子在58%至99%之间，具体取决于千伏峰值（kVp）和束流过滤情况。这些滤波器可在束流中平移和旋转，DTS利用来自成像系统的数字信号跟踪其运动。当确定射向皮肤给定一点的射线穿过补偿滤波器时，会应用适当的衰减校正。这些校正已成功纳入DTS软件，以更准确地确定皮肤剂量。
