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

Ebbe Laugaard Lorenzen*, Jesper Folsted Kallehauge, Camilla Skinnerup Byskov, Rikke Hedegaard Dahlrot, Charlotte Aaquist Haslund, Trine Lignell Guldberg, Yasmin Lassen-Ramshad, Slávka Lukacova, Aida Muhic, Petra Witt Nyström, Lene Haldbo-Classen, Ihsan Bahij, Lone Larsen, Britta Weber, Christian Rønn Hansen

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

6 Citations (Scopus)


BACKGROUND: 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.

MATERIAL AND METHODS: 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.

RESULTS: 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.

CONCLUSION: 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.

Original languageEnglish
JournalActa Oncologica
Issue number11
Pages (from-to)1548-1554
Number of pages7
Publication statusPublished - Nov 2021


  • Brain/diagnostic imaging
  • Humans
  • Observer Variation
  • Organs at Risk
  • Pilot Projects
  • Radiotherapy Planning, Computer-Assisted


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