Son Kihong, Chang Jieun, Lee Hoyeon, Kim Changhwan, Lee Taewon, Cho Seungryong, Park Sohyun, Kim Jin Sung
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, Yonsei University Health System, Seoul, Korea.
PLoS One. 2018 Feb 15;13(2):e0192933. doi: 10.1371/journal.pone.0192933. eCollection 2018.
To reduce the radiation dose given to patients, a tube current modulation (TCM) method has been widely used in diagnostic CT systems. However, the TCM method has not yet been applied to a kV-CBCT system on a LINAC machine. The purpose of this study is to investigate if a TCM method would be desirable in a kV-CBCT system for image-guided radiation therapy (IGRT) or not. We have developed an attenuation-based TCM method using prior knowledge from planning CT images of patients. The TCM method can provide optimized dose reductions without degrading image quality for kV-CBCT imaging. Here, we investigate whether or not our suggested TCM method is desirable to use in kV-CBCT systems to confirm and revise the exact position of a patient for IGRT. Patients go through diagnostic CT scans for RT planning; therefore, using information from prior CT images can enable estimations of the total X-ray attenuation through a patient's body in a CBCT setting for radiation treatment. Having this planning CT image allows to use the proposed TCM method in RT. The proposed TCM method provides a minimal amount of current for each projection, as well as total current, required to reconstruct the current modulated CBCT image with an image quality similar to that of CBCT. After applying a calculated TCM current for each projection, projection images were acquired and the current modulated CBCT image was reconstructed using a FDK algorithm. To validate the proposed approach, we used a numerical XCAT phantom and a real ATOM phantom and evaluated the performance of the proposed method via visual and quantitative image quality metrics. The organ dose due to imaging radiation was calculated in both cases and compared using the GATE simulation toolkit. As shown in the quantitative evaluation, normalized noise and SSIM values of the TCM were similar to those of conventional CBCT images. In addition, the proposed TCM method yielded comparable image quality to that of conventional CBCT images for both simulations and experimental studies as organ doses were decreased. We have successfully demonstrated the feasibility and dosimetric merit of a prototypical TCM method for kV-CBCT via simulations and experimental study. The results indicate that the proposed TCM method and overall framework can be a viable option for CBCT imaging that utilizes an optimal dose reduction without degrading image quality. Thus, this method reduces the probability for side effects due to radiation exposure.
为降低患者所接受的辐射剂量，管电流调制（TCM）方法已在诊断CT系统中广泛应用。然而，TCM方法尚未应用于直线加速器上的千伏锥形束CT（kV-CBCT）系统。本研究的目的是探讨在用于图像引导放射治疗（IGRT）的kV-CBCT系统中，TCM方法是否适用。我们利用患者计划CT图像的先验知识，开发了一种基于衰减的TCM方法。该TCM方法可为kV-CBCT成像提供优化的剂量降低，而不会降低图像质量。在此，我们研究我们所建议的TCM方法在kV-CBCT系统中用于确认和修正患者在IGRT中的精确位置是否适用。患者需进行诊断CT扫描以进行放疗计划；因此，利用先前CT图像的信息能够估计在CBCT放疗设置中穿过患者身体的总X射线衰减。有了这张计划CT图像，就能够在放疗中使用所提出的TCM方法。所提出的TCM方法为每个投影以及重建与CBCT图像质量相似的电流调制CBCT图像所需的总电流提供最小量的电流。在为每个投影应用计算出的TCM电流后，采集投影图像，并使用FDK算法重建电流调制CBCT图像。为验证所提出的方法，我们使用了数值XCAT体模和真实ATOM体模，并通过视觉和定量图像质量指标评估了所提出方法的性能。在两种情况下都计算了成像辐射所致的器官剂量，并使用GATE模拟工具包进行比较。如定量评估所示，TCM的归一化噪声和结构相似性指数（SSIM）值与传统CBCT图像的相似。此外，在所提出的TCM方法中，随着器官剂量降低，模拟和实验研究中的图像质量与传统CBCT图像相当。我们通过模拟和实验研究成功证明了用于kV-CBCT的原型TCM方法的可行性和剂量学优势。结果表明，所提出的TCM方法和总体框架对于在不降低图像质量的情况下实现最佳剂量降低的CBCT成像而言可能是一个可行的选择。因此，该方法降低了因辐射暴露导致副作用的可能性。
