Yoo Boyeol, Son Kihong, Pua Rizza, Kim Jinsung, Solodov Alexander, Cho Seungryong
Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology, Daejeon, Korea.
Department of Radiation Oncology, Yonsei Cancer Center, Yonsei University College of Medicine, Seoul, Korea.
Healthc Inform Res. 2016 Oct;22(4):316-325. doi: 10.4258/hir.2016.22.4.316. Epub 2016 Oct 31.
With the increased use of computed tomography (CT) in clinics, dose reduction is the most important feature people seek when considering new CT techniques or applications. We developed an intensity-weighted region-of-interest (IWROI) imaging method in an exact half-fan geometry to reduce the imaging radiation dose to patients in cone-beam CT (CBCT) for image-guided radiation therapy (IGRT). While dose reduction is highly desirable, preserving the high-quality images of the ROI is also important for target localization in IGRT.
An intensity-weighting (IW) filter made of copper was mounted in place of a bowtie filter on the X-ray tube unit of an on-board imager (OBI) system such that the filter can substantially reduce radiation exposure to the outer ROI. In addition to mounting the IW filter, the lead-blade collimation of the OBI was adjusted to produce an exact half-fan scanning geometry for a further reduction of the radiation dose. The chord-based rebinned backprojection-filtration (BPF) algorithm in circular CBCT was implemented for image reconstruction, and a humanoid pelvis phantom was used for the IWROI imaging experiment.
The IWROI image of the phantom was successfully reconstructed after beam-quality correction, and it was registered to the reference image within an acceptable level of tolerance. Dosimetric measurements revealed that the dose is reduced by approximately 61% in the inner ROI and by 73% in the outer ROI compared to the conventional bowtie filter-based half-fan scan.
The IWROI method substantially reduces the imaging radiation dose and provides reconstructed images with an acceptable level of quality for patient setup and target localization. The proposed half-fan-based IWROI imaging technique can add a valuable option to CBCT in IGRT applications.
随着计算机断层扫描（CT）在临床中的使用增加，在考虑新的CT技术或应用时，降低剂量是人们追求的最重要特性。我们开发了一种强度加权感兴趣区域（IWROI）成像方法，采用精确的半扇形几何结构，以降低锥形束CT（CBCT）用于图像引导放射治疗（IGRT）时对患者的成像辐射剂量。虽然降低剂量非常可取，但保留感兴趣区域的高质量图像对于IGRT中的靶区定位也很重要。
在机载成像仪（OBI）系统的X射线管单元上安装由铜制成的强度加权（IW）滤波器，以代替蝴蝶结滤波器，这样该滤波器可大幅减少对外侧感兴趣区域的辐射暴露。除了安装IW滤波器外，还调整了OBI的铅叶片准直，以产生精确的半扇形扫描几何结构，进一步降低辐射剂量。采用圆形CBCT中基于弦的重新分箱反投影滤波（BPF）算法进行图像重建，并使用仿人骨盆体模进行IWROI成像实验。
经束流质量校正后，成功重建了体模的IWROI图像，并在可接受的公差范围内与参考图像配准。剂量学测量表明，与传统的基于蝴蝶结滤波器的半扇形扫描相比，内侧感兴趣区域的剂量降低了约61%，外侧感兴趣区域的剂量降低了73%。
IWROI方法可大幅降低成像辐射剂量，并提供质量可接受的重建图像，用于患者摆位和靶区定位。所提出的基于半扇形的IWROI成像技术可为IGRT应用中的CBCT增添一个有价值的选项。
