A national study on the inter-observer variability in the delineation of organs at risk in the brain

The Danish Neuro Oncology Group (DNOG) has established national consensus guidelines for the delineation of organs at risk (OAR) structures based on published literature. This study was conducted to finalise these guidelines and evaluate the inter-observer variability of the delineated OAR structures by expert observers. The DNOG delineation guidelines were formed by participants from all Danish centres that treat brain tumours with radiotherapy. In a two-day workshop, guidelines were discussed and finalised based on a pilot study. Following this, the ten participants contoured the following OARs on T1-weighted gadolinium enhanced MRI from 13 patients with brain tumours: optic tracts, optic nerves, chiasm, spinal cord, brainstem, pituitary gland and hippocampus. The metrics used for comparison were the Dice similarity coefficient (Dice), mean surface distance (MSD) and others. A total of 968 contours were delineated across the 13 patients. On average eight (range six to nine) individual contour sets were made per patient. Good agreement was found across all structures with a median MSD below 1 mm for most structures, with the chiasm performing the best with a median MSD of 0.45 mm. The Dice was as expected highly volume dependent, the brainstem (the largest structure) had the highest Dice value with a median of 0.89 whereas smaller volumes such as the chiasm had a Dice of 0.71. Except for the caudal definition of the spinal cord, the variances observed in the contours of OARs in the brain were generally low and consistent. Surface mapping revealed sub-regions of higher variance for some organs. The data set is being prepared as a validation data set for auto-segmentation algorithms for use within the Danish Comprehensive Cancer Centre – Radiotherapy and potential collaborators.

丹麦神经肿瘤学小组（Danish Neuro Oncology Group, DNOG）基于已发表文献，制定了危及器官（Organs at Risk, OAR）轮廓勾画的全国共识指南。本研究旨在敲定上述指南，并评估专家观察者勾画危及器官结构的观察者间变异。DNOG勾画指南由丹麦所有开展脑肿瘤放射治疗的中心参与者共同制定。在为期两天的研讨会中，研究团队基于预试验对指南进行讨论并最终定稿。随后，10名参与者对13例脑肿瘤患者的钆增强T1加权MRI图像上的以下危及器官进行轮廓勾画：视束、视神经、视交叉、脊髓、脑干、垂体及海马。本次研究采用的评估指标包括戴斯相似性系数（Dice similarity coefficient, Dice）、平均表面距离（mean surface distance, MSD）等。本研究共完成968例器官轮廓勾画，覆盖全部13例患者，平均每例患者完成8组（范围6~9组）独立勾画。所有受检结构均展现出良好的一致性，多数结构的中位MSD低于1mm，其中视交叉表现最优，中位MSD达0.45mm。戴斯相似性系数如预期般高度依赖器官体积：体积最大的脑干戴斯系数最高，中位数为0.89；而体积较小的视交叉戴斯系数为0.71。除脊髓的尾侧勾画边界外，脑部危及器官的轮廓勾画变异总体较低且一致性良好。表面映射分析显示，部分器官存在变异程度较高的亚区域。本数据集目前正被整理为丹麦综合癌症中心放射治疗部门及潜在合作方所用的自动分割算法验证数据集。