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于早期识别和管理患者至关重要。一种临床诊断这种闭塞性疾病的新方法是应用同步辐射与碘K边减影血管造影术相结合，使用静脉注射造影剂。在该方法中，在略低于和高于碘K吸收边能量（33 keV）（~ 400 eV）处拍摄两个X射线图像。对两幅图像进行对数相减后，消除了非血管结构的背景，得到增强的血管图像。本研究的目的是开发一个蒙特卡罗程序来计算同步辐射血管造影术中病人的吸收剂量。电子和光子的输运码有很多种，其中EGS是最常用和最广泛应用的一种。EGS是用Mortran语言编写的，这是一种专门为代码开发的语言，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keV到几TeV，这使得代码对于诊断X射线应用来说太大了。因此，开发了一个专门适用于这些应用的小代码。

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.