Feasibility of a Direct-Conversion Method from Magnetic Susceptibility to Relative Electron Density for Radiation Therapy Treatment Planning

作     者：Kengo Ito Noriyuki Kadoya Yujiro Nakajima Masahide Saito Kiyokazu Sato Tatsuo Nagasaka Kazuomi Yamanaka Suguru Dobashi Ken Takeda Haruo Matsushita Keiichi Jingu 

作者机构：Department of Radiation Oncology Tohoku University Graduate School of Medicine Sendai Japan Department of Radiology Tokyo Metropolitan Komagome Hospital Tokyo Japan Department of Radiology University of Yamanashi Chuo-shi Japan Department of Radiology Tohoku University Hospital Sendai Japan Department of Therapeutic Radiology Tohoku University School of Medicine Sendai Japan 

出 版 物：《International Journal of Medical Physics, Clinical Engineering and Radiation Oncology》 (医学物理学、临床工程、放射肿瘤学（英文）)

年 卷 期：2017年第6卷第3期

页      面：252-265页

学科分类：1002[医学-临床医学] 100214[医学-肿瘤学] 10[医学] 

主　　题：Magnetic Susceptibility Quantitative Susceptibility Mapping MRI-Based Radiation Therapy Planning 

摘      要：Recently, several institutions have been developing magnetic resonance imaging (MRI)-guided radiotherapy treatment systems. In this study, we examine whether it is possible to perform radiation therapy planning (RTP) using a magnetic susceptibility map obtained using MRI. The head of a healthy volunteer was scanned using dual-energy computed tomography (CT) and MRI. A T2-star-weighted 3D gradient echo-based sequence (GRE) with images taken at four different echo times was acquired using the MRI scanner. The CT images were converted to relative electron density (rED) using a predefined ΔCT-rED conversion table. ΔCT was derived using the energy-subtraction method. The rED map was obtained from a single-linear relationship with the ΔCT-rED conversion table, whereas the magnetic susceptibility map was obtained from quantitative susceptibility mapping (QSM) via MRI. Subsequently, to obtain the relationship between the magnetic susceptibility and the rED, the rED map was rigidly aligned to the susceptibility map and resampled at the susceptibility map’s resolution. Finally, the magnetic susceptibility rED conversion table was obtained via voxel-by-voxel mapping between the two maps. No strong relationship between magnetic susceptibility and rED was obtained in the healthy volunteer’s head or in this study. The coefficient correlation between these parameters was 0.0145. Magnetic susceptibility values may be not able to convert to rED using our proposed method in healthy volunteer’s head. In contrast to the magnetic-susceptibility values obtained from the QSM algorithm, which were strongly affected by calcification and iron content, the rED or CT number was not considerably affected by such materials.