Medical Physics Program, Department of Physics and Applied Physics, University of Massachusetts Lowell, Lowell, MA, United States of America. Brigham and Women's Hospital, Dana Farber Cancer Institute and Harvard Medical School, Boston, MA, United States of America.
Phys Med Biol. 2020 Jul 6;65(13):135004. doi: 10.1088/1361-6560/ab868a.
Intensive computation time is required to simulate images of electronic portal imaging device (EPID) using Monte Carlo (MC) technique, limiting the development of applications associated with EPID, such as mega-voltage cone-beam computed tomography (MV-CBCT). In this study, a fast, accurate simulation strategy for MV-CBCT utilizing the FastEPID technique has been developed and validated. During FastEPID simulation, photon detection was determined by pre-calculated photon energy deposition efficiency (η) and particle transport within the EPID was replaced with a pre-calculated optical photon spread function. This method is capable of reducing the time required for EPID image simulation by a factor of 90-140, without compromising image quality. MV-CBCT images reconstructed from the FastEPID simulated projections have been validated against measurement in terms of mean Hounsfield unit (HU), noise, and cupping artifact. These images were obtained with both a Catphan 604 phantom and an anthropomorphic pelvis phantom, under treatment beam energies of 2.5 MV, 6 MV, and 6 MV flattening filter free. The agreement between measurement and simulation was excellent in all cases. This novel strategy was capable of reducing the run time of a full scan simulation of MV-CBCT performed on a CPU cluster to a matter of hours, rather than weeks or months required by a conventional approach. Multiple applications associated with MV-CBCT (e.g. imager design optimization) are anticipated to gain from the implementation of this novel simulation strategy.
使用蒙特卡罗 (MC) 技术模拟电子射野影像装置 (EPID) 的图像需要大量的计算时间，这限制了与 EPID 相关的应用程序的开发，例如兆伏锥形束计算机断层扫描 (MV-CBCT)。在这项研究中，开发并验证了一种利用 FastEPID 技术的快速、准确的 MV-CBCT 模拟策略。在 FastEPID 模拟中，通过预先计算的光子能量沉积效率 (η) 来确定光子检测，并用预先计算的光学光子扩展函数代替 EPID 内的粒子传输。这种方法能够将 EPID 图像模拟所需的时间减少 90-140 倍，而不会影响图像质量。利用 FastEPID 模拟的投影重建的 MV-CBCT 图像在平均亨氏单位 (HU)、噪声和杯状伪影方面与测量值进行了验证。这些图像是使用 Catphan 604 体模和人体骨盆体模在治疗束能量为 2.5 MV、6 MV 和 6 MV 无平坦滤过器的情况下获得的。在所有情况下，测量值和模拟值之间的一致性都非常好。这种新策略能够将在 CPU 集群上进行的 MV-CBCT 全扫描模拟的运行时间从数周或数月缩短到数小时，而传统方法则需要数周或数月。预计与 MV-CBCT 相关的多个应用程序（例如成像仪设计优化）将从实施这种新的模拟策略中受益。
