Fatemi Ali, Taghizadeh Somayeh, Yang Claus Chunli, R Kanakamedala Madhava, Morris Bart, Vijayakumar Srinivasan
Radiation Oncology/radiology, University of Mississippi Medical Center.
Radiation Oncology, University of Mississippi Medical Center.
Cureus. 2017 Dec 18;9(12):e1957. doi: 10.7759/cureus.1957.
Purpose Magnetic resonance (MR) images are necessary for accurate contouring of intracranial targets, determination of gross target volume and evaluation of organs at risk during stereotactic radiosurgery (SRS) treatment planning procedures. Many centers use magnetic resonance imaging (MRI) simulators or regular diagnostic MRI machines for SRS treatment planning; while both types of machine require two stages of quality control (QC), both machine- and patient-specific, before use for SRS, no accepted guidelines for such QC currently exist. This article describes appropriate machine-specific QC procedures for SRS applications. Methods and materials We describe the adaptation of American College of Radiology (ACR)-recommended QC tests using an ACR MRI phantom for SRS treatment planning. In addition, commercial Quasar MRID and Quasar GRID phantoms were used to evaluate the effects of static magnetic field (B) inhomogeneity, gradient nonlinearity, and a Leksell G frame (SRS frame) and its accessories on geometrical distortion in MR images. Results QC procedures found in-plane distortions (Maximum = 3.5 mm, Mean = 0.91 mm, Standard deviation = 0.67 mm, >2.5 mm (%) = 2) in X-direction (Maximum = 2.51 mm, Mean = 0.52 mm, Standard deviation = 0.39 mm, > 2.5 mm (%) = 0) and in Y-direction (Maximum = 13. 1 mm , Mean = 2.38 mm, Standard deviation = 2.45 mm, > 2.5 mm (%) = 34) in Z-direction and < 1 mm distortion at a head-sized region of interest. MR images acquired using a Leksell G frame and localization devices showed a mean absolute deviation of 2.3 mm from isocenter. The results of modified ACR tests were all within recommended limits, and baseline measurements have been defined for regular weekly QC tests. Conclusions With appropriate QC procedures in place, it is possible to routinely obtain clinically useful MR images suitable for SRS treatment planning purposes. MRI examination for SRS planning can benefit from the improved localization and planning possible with the superior image quality and soft tissue contrast achieved under optimal conditions.
目的 在立体定向放射外科（SRS）治疗计划制定过程中，磁共振（MR）图像对于准确勾勒颅内靶区、确定大体靶体积以及评估危及器官至关重要。许多中心在SRS治疗计划制定中使用磁共振成像（MRI）模拟器或常规诊断MRI机器；虽然这两种类型的机器在用于SRS之前都需要两个阶段的质量控制（QC），包括针对机器和患者的特定控制，但目前尚无此类QC的公认指南。本文描述了适用于SRS应用的特定于机器的QC程序。方法和材料 我们描述了使用美国放射学会（ACR）推荐的QC测试，并采用ACR MRI体模进行SRS治疗计划制定。此外，还使用了商业Quasar MRID和Quasar GRID体模来评估静磁场（B）不均匀性、梯度非线性以及Leksell G型框架（SRS框架）及其附件对MR图像几何畸变的影响。结果 QC程序发现，在平面内，X方向的畸变（最大值 = 3.5毫米，平均值 = 0.91毫米，标准差 = 0.67毫米，>2.5毫米（%） = 2），Y方向的畸变（最大值 = 2.51毫米，平均值 = 0.52毫米，标准差 = 0.39毫米，>2.5毫米（%） = 0），Z方向的畸变（最大值 = 13.1毫米，平均值 = 2.38毫米，标准差 = 2.45毫米，>2.5毫米（%） = 34），并且在头部大小的感兴趣区域内畸变小于1毫米。使用Leksell G型框架和定位装置采集的MR图像显示与等中心的平均绝对偏差为2.3毫米。修改后的ACR测试结果均在推荐限值内，并且已为常规每周QC测试定义了基线测量值。结论 通过适当的QC程序，有可能常规获得适用于SRS治疗计划目的的临床有用MR图像。SRS计划的MRI检查可受益于在最佳条件下实现的卓越图像质量和软组织对比度所带来的改进定位和计划。
