Ziemann Christian, Stille Maik, Cremers Florian, Buzug Thorsten M, Rades Dirk
Department of Radiotherapy, University Medical Center Schleswig Holstein/Campus Luebeck, Luebeck, Germany.
Institute of Medical Engineering, University of Luebeck, Luebeck, Germany.
J Appl Clin Med Phys. 2018 May;19(3):227-233. doi: 10.1002/acm2.12325. Epub 2018 Apr 17.
Metal artifacts caused by high-density implants lead to incorrectly reconstructed Hounsfield units in computed tomography images. This can result in a loss of accuracy in dose calculation in radiation therapy. This study investigates the potential of the metal artifact reduction algorithms, Augmented Likelihood Image Reconstruction and linear interpolation, in improving dose calculation in the presence of metal artifacts.
In order to simulate a pelvis with a double-sided total endoprosthesis, a polymethylmethacrylate phantom was equipped with two steel bars. Artifacts were reduced by applying the Augmented Likelihood Image Reconstruction, a linear interpolation, and a manual correction approach. Using the treatment planning system Eclipse™, identical planning target volumes for an idealized prostate as well as structures for bladder and rectum were defined in corrected and noncorrected images. Volumetric modulated arc therapy plans have been created with double arc rotations with and without avoidance sectors that mask out the prosthesis. The irradiation plans were analyzed for variations in the dose distribution and their homogeneity. Dosimetric measurements were performed using isocentric positioned ionization chambers.
Irradiation plans based on images containing artifacts lead to a dose error in the isocenter of up to 8.4%. Corrections with the Augmented Likelihood Image Reconstruction reduce this dose error to 2.7%, corrections with linear interpolation to 3.2%, and manual artifact correction to 4.1%. When applying artifact correction, the dose homogeneity was slightly improved for all investigated methods. Furthermore, the calculated mean doses are higher for rectum and bladder if avoidance sectors are applied.
Streaking artifacts cause an imprecise dose calculation within irradiation plans. Using a metal artifact correction algorithm, the planning accuracy can be significantly improved. Best results were accomplished using the Augmented Likelihood Image Reconstruction algorithm.
高密度植入物引起的金属伪影会导致计算机断层扫描图像中Hounsfield单位重建错误。这可能会导致放射治疗剂量计算的准确性丧失。本研究探讨了增强似然图像重建和线性插值等金属伪影减少算法在存在金属伪影时改善剂量计算的潜力。
为了模拟带有双侧全内置假体的骨盆，在聚甲基丙烯酸甲酯体模中配备两根钢筋。通过应用增强似然图像重建、线性插值和手动校正方法来减少伪影。使用治疗计划系统Eclipse™，在校正和未校正图像中为理想化前列腺以及膀胱和直肠结构定义相同的计划靶体积。已经创建了具有双弧旋转且有和没有避开假体的避开扇形区的容积调强弧形治疗计划。分析照射计划的剂量分布变化及其均匀性。使用等中心定位的电离室进行剂量测量。
基于包含伪影的图像的照射计划导致等中心处的剂量误差高达8.4%。使用增强似然图像重建进行校正可将此剂量误差降低至2.7%，使用线性插值校正至3.2%，手动伪影校正至4.1%。应用伪影校正时，所有研究方法的剂量均匀性均略有改善。此外，如果应用避开扇形区，直肠和膀胱的计算平均剂量会更高。
条纹伪影会导致照射计划中的剂量计算不准确。使用金属伪影校正算法可显著提高计划准确性。使用增强似然图像重建算法可获得最佳结果。
