Development of a Patient Absorbed Dose Calculation Code for Subtraction Angiography Using Synchrotron Radiation

冠状动脉闭塞性疾病可导致致命的心脏病发作，在工业化国家很常见。了解血管闭塞的发展阶段及其位置对患者的早期识别和治疗至关重要。应用同步辐射联合碘k -边缘减影血管造影（静脉注射造影剂），在碘k -吸收边缘（33keV）能量略（-400eV）以下和略（-400eV）以上拍摄两张x线图像，是临床诊断这种闭塞性疾病的新方法。对两幅图像进行对数相减，消除非血管体结构的背景，得到增强的血管图像。包括日本筑波光子工厂在内的世界上几个同步加速器设施正在进行研究。本研究的目的是开发一个蒙特卡罗代码来计算患者在使用同步辐射减影血管造影期间的吸收剂量。电子和光子的输运码有几种，其中EGS输运码最为常见，在各个领域应用最为广泛。EGS是用专门为代码开发的语言Mortran编写的，不熟悉该语言的用户需要将代码翻译成FORTRAN。此外，EGS可以处理的能量范围非常宽，从几个keV到几个TeV，这使得代码对于诊断x射线应用来说太大了。因此，专门针对这些应用程序开发了一个小代码。

Occlusive disease of the coronary artery, which can result in a fatal heart attack, is common in industrialized countries. Understanding of the stage of the development of the vessel occlusion as well as its location is essential for early recognition and management of the patients. A new method for clinical diagnosis of such occlusive disease is an application of synchrotron radiation combined with iodine K-edge subtraction angiography using an intravenous injection of a contrast medium In this method two X-ray images are taken at slightly (-400eV) below and above the energy of iodine K-absorption edge (33keV). After logarithmic subtraction of the two images all the background due to nonvascular body structures are eliminated, and an enhanced vascular image is obtained. Studies are being carried on at several synchrotron facilities in the world including photon Factory in Tsukuba, Japan.The purpose of this study it to develop a Monte Carlo code to calculate patient absorbed dose during subtraction angiography using synchrotron radiation. There exist several transport codes for electrons and photons, among which EGS is most commonly and widely used in various fields. EGS is written in Mortran, a language especially developed for the code, and the users who are not familiar to the language are required to translate the code into FORTRAN.Further, the energy range that EGS can handle is very broad, from a few keV to several TeV,which makes the code rather too large for diagnostic X-ray applications. Therefore, a small code has been developed applicable specifically for these applications.