Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.
Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia.
Med Phys. 2020 Apr;47(4):1920-1929. doi: 10.1002/mp.14016. Epub 2020 Jan 28.
Dynamic dosimaging is a concept whereby a detector in motion is tracked with magnetic resonance imaging (MRI) to validate the amount and position of dose in a radiation therapy treatment on an MRI-linac. This work takes steps toward the realization of dynamic dosimaging with the novel high resolution silicon array detector: MagicPlate-512 (M512). The performance of the M512 was assessed in a 1.0 T inline MRI-linac, without simultaneous imaging and then during an imaging sequence, both during dosimetry. MR images were acquired to determine the effect of the detector and its components on image quality.
Beam profiles were measured using the M512 on the Australian MRI-Linac and a comparison made with Gafchromic EBT3 film to investigate any intrinsic magnetic field effects in the silicon. The M512 has 512 sensitive volumes, each 0.5 × 0.5 × 0.037 mm in dimension, organized in a two-dimensional array. Small field sizes up to 4.2 × 3.8 cm were investigated in both solid water and then solid lung phantoms. Beam profiles taken at 1.0 T were compared to 0 T conditions, and also to profiles taken during a gradient echo (GRE) imaging sequence. Differences in 80%-20% penumbral width and full width at half maximum (FWHM) were investigated. Localizer MR images were acquired of the detector adjacent to a water phantom.
Good agreement was observed between the M512 and film, with average differences in penumbral width and FWHM of <1 mm in the absence of the imaging sequence. Concurrent imaging widened the penumbra by up to 1.2 mm due to RF noise affecting the detector; film profiles were unchanged. Magnetic resonance images were affected by noise, in particular, due to the large amount of aluminum present, as well as from the USB cable, which acted as an antenna. Unfortunately, due to these issues, suitable dynamic dose imaging was not achieved with the current M512/phantom configuration and the MRI-linac. However, progress was made toward achieving this goal for future work.
The M512 silicon array detector successfully measured high-resolution beam profiles in agreement with Gafchromic film to within an average of <1 mm on the first MRI-linac in Australia. More effective noise reduction will be required for the achievement of dynamic dosimaging in the future.
动态剂量成像（Dynamic dosimaging）是一种概念，通过磁共振成像（MRI）跟踪运动中的探测器，以验证放射治疗中在 MRI 直线加速器上的剂量的数量和位置。这项工作朝着使用新型高分辨率硅阵列探测器：MagicPlate-512（M512）实现动态剂量成像迈出了一步。在没有同时成像的情况下，在 1.0T 直线加速器内对 M512 的性能进行了评估，然后在成像序列期间，同时在剂量测量期间进行了评估。采集 MR 图像以确定探测器及其组件对图像质量的影响。
使用 M512 在澳大利亚 MRI 直线加速器上测量束流轮廓，并与 Gafchromic EBT3 胶片进行比较，以研究硅中的任何固有磁场效应。M512 有 512 个敏感体积，每个体积为 0.5×0.5×0.037mm，呈二维阵列排列。在固体水和固体肺体模中研究了小至 4.2×3.8cm 的小射野尺寸。在 1.0T 时采集的束流轮廓与 0T 条件进行了比较，也与梯度回波（GRE）成像序列期间采集的轮廓进行了比较。研究了 80%-20%半影宽度和全宽半高（FWHM）的差异。在靠近水模体的探测器附近采集定位器 MR 图像。
M512 和胶片之间观察到良好的一致性，在不存在成像序列的情况下，半影宽度和 FWHM 的平均差异小于 1mm。由于射频噪声影响探测器，同时成像会使半影变宽多达 1.2mm；胶片轮廓不变。磁共振图像受到噪声的影响，特别是由于存在大量的铝，以及 USB 电缆，它充当了天线。不幸的是，由于这些问题，当前的 M512/体模配置和 MRI 直线加速器无法实现合适的动态剂量成像。然而，为未来的工作实现这一目标取得了进展。
M512 硅阵列探测器成功地在澳大利亚第一台 MRI 直线加速器上以与 Gafchromic 胶片平均小于 1mm 的精度测量了高分辨率束流轮廓。未来实现动态剂量成像将需要更有效的降噪。
