Department of Radiation Oncology, Sunshine Coast University Hospital, Birtinya, QLD, Australia.
ICON Cancer Centre, Maroochydore, QLD, Australia.
Br J Radiol. 2020 Oct 1;93(1114):20200543. doi: 10.1259/bjr.20200543. Epub 2020 Sep 2.
To evaluate interobserver agreement for weighted (W) and diffusion-weighted MRI (DW-MRI) contours of locally advanced rectal cancer (LARC); and to evaluate manual and semi-automated delineations of restricted diffusion tumour subvolumes.
20 cases of LARC were reviewed by 2 radiation oncologists and 2 radiologists. Contours of gross tumour volume (GTV) on W, DW-MRI and co-registered W/DW-MRI were independently delineated and compared using Dice Similarity Coefficient (DSC), mean distance to agreement (MDA) and other metrics of interobserver agreement. Restricted diffusion subvolumes within GTVs were manually delineated and compared to semi-automatically generated contours corresponding to intratumoral apparent diffusion coefficient (ADC) centile values.
Observers were able to delineate subvolumes of restricted diffusion with moderate agreement (DSC 0.666, MDA 1.92 mm). Semi-automated segmentation based on the 40th centile intratumoral ADC value demonstrated moderate average agreement with consensus delineations (DSC 0.581, MDA 2.44 mm), with errors noted in image registration and luminal variation between acquisitions. A small validation set of four cases with optimised planning MRI demonstrated improvement (DSC 0.669, MDA 1.91 mm).
Contours based on co-registered W and DW-MRI could be used for delineation of biologically relevant tumour subvolumes. Semi-automated delineation based on patient-specific intratumoral ADC thresholds may standardise subvolume delineation if registration between acquisitions is sufficiently accurate.
This is the first study to evaluate the feasibility of semi-automated diffusion-based subvolume delineation in LARC. This approach could be applied to dose escalation or 'dose painting' protocols to improve delineation reproducibility.
评估局部晚期直肠癌（LARC）加权（W）和弥散加权 MRI（DW-MRI）轮廓的观察者间一致性；并评估受限弥散肿瘤亚体积的手动和半自动勾画。
20 例 LARC 患者由 2 名放射肿瘤学家和 2 名放射科医生进行回顾性分析。分别独立勾画 W、DW-MRI 和 W/DW-MRI 配准的大体肿瘤体积（GTV）轮廓，并使用 Dice 相似系数（DSC）、平均一致性距离（MDA）和其他观察者间一致性指标进行比较。手动勾画 GTV 内的受限弥散亚体积，并与对应肿瘤内表观弥散系数（ADC）百分位数值的半自动生成轮廓进行比较。
观察者能够勾画具有中度一致性的受限弥散亚体积（DSC 0.666，MDA 1.92mm）。基于肿瘤内 ADC 值第 40 百分位数的半自动分割与共识勾画具有中度平均一致性（DSC 0.581，MDA 2.44mm），在图像配准和采集之间的管腔变化方面存在误差。对 4 例优化计划 MRI 的小验证集进行评估，结果有所改善（DSC 0.669，MDA 1.91mm）。
基于配准的 W 和 DW-MRI 勾画的轮廓可用于勾画具有生物学相关性的肿瘤亚体积。如果采集之间的配准足够准确，基于患者特定的肿瘤内 ADC 阈值的半自动勾画可能会使亚体积勾画标准化。
这是第一项评估在 LARC 中应用基于弥散半自动勾画亚体积的可行性的研究。这种方法可应用于剂量递增或“剂量描绘”方案，以提高勾画的可重复性。
