Investigation of the clinical inter-observer bias in prostate fiducial marker image registration between CT and MR images

Emilia Persson, Sevgi Emin, Jonas Scherman, Christian Jamtheim Gustafsson, Patrik Brynolfsson, Sofie Ceberg, Adalsteinn Gunnlaugsson, Lars E. Olsson

Research output: Contribution to journalArticlepeer-review


Background and purpose: Inter-modality image registration between computed tomography (CT) and magnetic resonance (MR) images is associated with systematic uncertainties and the magnitude of these uncertainties is not well documented. The purpose of this study was to investigate the potential uncertainty of gold fiducial marker (GFM) registration for localized prostate cancer and to estimate the inter-observer bias in a clinical setting. Methods: Four experienced observers registered CT and MR images for 42 prostate cancer patients. Manual GFM identification was followed by a landmark-based registration. The absolute difference between observers in GFM identification and the displacement of the clinical target volume (CTV) was investigated. The CTV center of mass (CoM) vector displacements, DICE-index and Hausdorff distances for the observer registrations were compared against a clinical baseline registration. The time allocated for the manual registrations was compared. Results: Absolute difference in GFM identification between observers ranged from 0.0 to 3.0 mm. The maximum CTV CoM displacement from the clinical baseline was 3.1 mm. Displacements larger than or equal to 1 mm, 2 mm and 3 mm were 46%, 18% and 4%, respectively. No statistically significant difference was detected between observers in terms of CTV displacement. Median DICE-index and Hausdorff distance for the CTV, with their respective ranges were 0.94 [0.70–1.00] and 2.5 mm [0.7–8.7]. Conclusions: Registration of CT and MR images using GFMs for localized prostate cancer patients was subject to inter-observer bias on an individual patient level. A CTV displacement as large as 3 mm occurred for individual patients. These results show that GFM registration in a clinical setting is associated with uncertainties, which motivates the removal of inter-modality registrations in the radiotherapy workflow and a transition to an MRI-only workflow for localized prostate cancer.

Original languageEnglish
Article number150
JournalRadiation Oncology
Issue number1
Publication statusPublished - 2021 Dec

Bibliographical note

Funding Information:
Open access funding provided by Lund University. This work was supported by Gentle Radiotherapy and The Swedish Agency for Innovation systems (VINNOVA) under Grant 2016-03847 and 2016-02529, “Allmänna sjukhusets I Malmö Stiftelse för bekämpande av cancer”; Fru Berta Kamprads stiftelse för utforskning och bekämpning av cancersjukdomar, Lund, SUS foundations, Region Skåne and by “Onkologiska klinikens stiftelse för bekämpande av cancer”.

Publisher Copyright:
© 2021, The Author(s).

Copyright 2021 Elsevier B.V., All rights reserved.

Subject classification (UKÄ)

  • Other Physics Topics
  • Radiology, Nuclear Medicine and Medical Imaging

Free keywords

  • Computed tomography
  • Fiducial marker
  • Image registration
  • Inter-observer
  • Magnetic resonance imaging
  • Prostate cancer
  • Registration uncertainty


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