Szczykutowicz Timothy P, Hermus James, Geurts Mark, Smilowitz Jennifer
Department of Radiology, University of Wisconsin-Madison, Madison WI 53705, USA. Department of Medical Physics, University of Wisconsin-Madison, Madison WI 53705, USA. Department of Biomedical Engineering, University of Wisconsin-Madison, WI 53706, USA.
Phys Med Biol. 2015 Sep 21;60(18):7245-57. doi: 10.1088/0031-9155/60/18/7245. Epub 2015 Sep 8.
The multi-leaf collimator (MLC) assembly present on TomoTherapy (Accuray, Madison WI) radiation therapy (RT) and mega voltage CT machines is well suited to perform fluence field modulated CT (FFMCT). In addition, there is a demand in the RT environment for FFMCT imaging techniques, specifically volume of interest (VOI) imaging. A clinical TomoTherapy machine was programmed to perform VOI. Four different size ROIs were placed at varying distances from isocenter. Projections intersecting the VOI received 'full dose' while those not intersecting the VOI received 30% of the dose (i.e. the incident fluence for non VOI projections was 30% of the incident fluence for projections intersecting the VOI). Additional scans without fluence field modulation were acquired at 'full' and 30% dose. The noise (pixel standard deviation) and mean CT number were measured inside the VOI region and compared between the three scans. Dose maps were generated using a dedicated TomoTherapy treatment planning dose calculator. The VOI-FFMCT technique produced an image noise 1.05, 1.00, 1.03, and 1.05 times higher than the 'full dose' scan for ROI sizes of 10 cm, 13 cm, 10 cm, and 6 cm respectively within the VOI region. The VOI-FFMCT technique required a total imaging dose equal to 0.61, 0.69, 0.60, and 0.50 times the 'full dose' acquisition dose for ROI sizes of 10 cm, 13 cm, 10 cm, and 6 cm respectively within the VOI region. Noise levels can be almost unchanged within clinically relevant VOIs sizes for RT applications while the integral imaging dose to the patient can be decreased, and/or the image quality in RT can be dramatically increased with no change in dose relative to non-FFMCT RT imaging. The ability to shift dose away from regions unimportant for clinical evaluation in order to improve image quality or reduce imaging dose has been demonstrated. This paper demonstrates that FFMCT can be performed using the MLC on a clinical TomoTherapy machine for the first time.
托姆刀（Accuray公司，威斯康星州麦迪逊市）放射治疗（RT）机和兆伏级CT机上配备的多叶准直器（MLC）组件非常适合进行注量场调制CT（FFMCT）。此外，在放射治疗环境中对FFMCT成像技术有需求，特别是感兴趣体积（VOI）成像。对一台临床托姆刀机器进行编程以执行VOI。在距等中心不同距离处放置了四个不同大小的感兴趣区域（ROI）。与VOI相交的投影接收“全剂量”，而不与VOI相交的投影接收30%的剂量（即非VOI投影的入射注量是与VOI相交投影的入射注量的30%）。在“全”剂量和30%剂量下进行了无注量场调制的额外扫描。在VOI区域内测量噪声（像素标准差）和平均CT值，并在三次扫描之间进行比较。使用专用的托姆刀治疗计划剂量计算器生成剂量图。对于VOI区域内大小分别为10厘米、13厘米、10厘米和6厘米的ROI，VOI - FFMCT技术产生的图像噪声分别比“全剂量”扫描高1.05、1.00、1.03和1.05倍。对于VOI区域内大小分别为10厘米、13厘米、10厘米和6厘米的ROI，VOI - FFMCT技术所需的总成像剂量分别等于“全剂量”采集剂量的0.61、0.69、0.60和0.50倍。对于放射治疗应用，在临床相关的VOI大小范围内，噪声水平几乎可以保持不变，同时可以降低患者的整体成像剂量，和/或在不改变相对于非FFMCT放射治疗成像剂量的情况下显著提高放射治疗中的图像质量。已经证明了将剂量从对临床评估不重要的区域转移以提高图像质量或降低成像剂量的能力。本文首次证明了可以在临床托姆刀机器上使用MLC进行FFMCT。
