Raghavan Govind, Kishan Amar U, Cao Minsong, Chen Allen M
Department of Radiation Oncology, University of California, Los Angeles, David Geffen School of Medicine, Los Angeles, CA, USA.
Br J Radiol. 2016 Nov;89(1067):20160624. doi: 10.1259/bjr.20160624. Epub 2016 Sep 21.
Prior studies have relied on CT to assess alterations in anatomy among patients undergoing radiation for head and neck cancer. We sought to determine the feasibility of using MRI-based image-guided radiotherapy to quantify these changes and to ascertain their potential dosimetric implications.
6 patients with head and neck cancer were treated with intensity-modulated radiotherapy (IMRT) on a novel tri-Co teletherapy system equipped with a 0.35-T MRI (VR, ViewRay Incorporated, Oakwood Village, OH) to 66-70 Gy in 33 fractions (fx). Pre-treatment MRIs on Fx 1, 5, 10, 15, 20, 25, 30 and 33 were imported into a contouring interface, where the primary gross tumour volume (GTV) and parotid glands were delineated. The centre of mass (COM) shifts for these structures were assessed relative to Day 1. Dosimetric data were co-registered with the MRIs, and doses to the GTV and parotid glands were assessed.
Primary GTVs decreased significantly over the course of IMRT (median % volume loss, 38.7%; range, 29.5-72.0%; p < 0.05) at a median rate of 1.2%/fx (range, 0.92-2.2%/fx). Both the ipsilateral and contralateral parotid glands experienced significant volume loss (p < 0.05, for all) and shifted medially during IMRT. Weight loss correlated significantly with parotid gland volume loss and medial COM shift (p < 0.05).
Integrated on-board MRI can be used to accurately contour and analyze primary GTVs and parotid glands over the course of IMRT. COM shifts and significant volume reductions were observed, confirming the results of prior CT-based exercises. Advances in knowledge: The superior resolution of on-board MRI may facilitate online adaptive replanning in the future.
既往研究依靠CT评估头颈部癌放疗患者的解剖结构改变。我们试图确定使用基于MRI的图像引导放射治疗来量化这些变化并确定其潜在剂量学影响的可行性。
6名头颈部癌患者在配备0.35-T MRI（VR，ViewRay公司，俄亥俄州奥克伍德村）的新型三钴远距离治疗系统上接受调强放射治疗（IMRT），分33次分割给予66-70 Gy。将第1、5、10、15、20、25、30和33次分割时的治疗前MRI导入轮廓勾画界面，勾画出原发大体肿瘤体积（GTV）和腮腺。评估这些结构相对于第1天的质心（COM）移位。将剂量学数据与MRI进行配准，并评估GTV和腮腺的剂量。
在IMRT过程中，原发GTV显著缩小（体积损失中位数为38.7%；范围为29.5%-72.0%；p<0.05），中位缩小率为1.2%/次分割（范围为0.92%-2.2%/次分割）。同侧和对侧腮腺均出现显著体积损失（所有p<0.05），并在IMRT期间向内侧移位。体重减轻与腮腺体积损失和质心内侧移位显著相关（p<0.05）。
集成在治疗台上的MRI可用于在IMRT过程中准确勾画和分析原发GTV和腮腺。观察到质心移位和显著的体积减小，证实了既往基于CT研究的结果。知识进展：治疗台上MRI的卓越分辨率可能有助于未来的在线自适应重新计划。
