Interobserver variation in tumor delineation of liver metastases using Magnetic Resonance Imaging

Julia E Peltenburg; Ali Hosni; Rana Bahij; Simon Boeke; Pètra M Braam; William A Hall; Martijn P W Intven; Luca Nicosia; Jan-Jakob Sonke; Marnix Witte; Marlies E Nowee; Tomas Janssen

doi:10.1016/j.phro.2024.100592

Interobserver variation in tumor delineation of liver metastases using Magnetic Resonance Imaging

Phys Imaging Radiat Oncol. 2024 May 27:30:100592. doi: 10.1016/j.phro.2024.100592. eCollection 2024 Apr.

Authors

Affiliations

¹ Department of Radiation Oncology, The Netherlands Cancer Institute, Postal Address: Plesmanlaan 121, 1066CX Amsterdam, The Netherlands.
² Department of Radiation Oncology, Princess Margaret Cancer Center, Postal Address: 610 University Avenue, Toronto, ON M5G 2M9, Canada.
³ Department of Oncology, Odense University Hospital, Postal Address: J. B. Winsløws Vej 4, 5000 Odense, Denmark.
⁴ Department of Radiation Oncology, Tübingen University Hospital, Postal Address: Geissweg 3, 72076 Tübingen, Germany.
⁵ Department of Radiation Oncology, Radboud University Medical Center, Postal Address: Geert Grooteplein Zuid 10, 6525 GA, Nijmegen, The Netherlands.
⁶ Department of Radiation Oncology, Medical College of Wisconsin, Postal Address: 9200 W. Wisconsin Avenue, Milwaukee, WI 53226, USA.
⁷ Department of Radiation Oncology, University Medical Center Utrecht, Postal Address: Heidelberglaan 100, 3584 CX, Utrecht, The Netherlands.
⁸ Department of Radiation Oncology, Sacro Cuore Don Calabria Hospital, Postal Address: Viale Luigi Rizzardi, 4, 37024, Negrar di Valpolicella VR, Italy.

Abstract

Background and purpose: Magnetic Resonance Imaging (MRI) guided stereotactic body radiotherapy (SBRT) of liver metastases is an upcoming high-precision non-invasive treatment. Interobserver variation (IOV) in tumor delineation, however, remains a relevant uncertainty for planning target volume (PTV) margins. The aims of this study were to quantify IOV in MRI-based delineation of the gross tumor volume (GTV) of liver metastases and to detect patient-specific factors influencing IOV.

Materials and methods: A total of 22 patients with liver metastases from three primary tumor origins were selected (colorectal(8), breast(6), lung(8)). Delineation guidelines and planning MRI-scans were provided to eight radiation oncologists who delineated all GTVs. All delineations were centrally peer reviewed to identify outliers not meeting the guidelines. Analyses were performed both in- and excluding outliers. IOV was quantified as the standard deviation (SD) of the perpendicular distance of each observer's delineation towards the median delineation. The correlation of IOV with shape regularity, tumor origin and volume was determined.

Results: Including all delineations, average IOV was 1.6 mm (range 0.6-3.3 mm). From 160 delineations, in total fourteen single delineations were marked as outliers after peer review. After excluding outliers, the average IOV was 1.3 mm (range 0.6-2.3 mm). There was no significant correlation between IOV and tumor origin or volume. However, there was a significant correlation between IOV and regularity (Spearman's ρ_s = -0.66; p = 0.002).

Conclusion: MRI-based IOV in tumor delineation of liver metastases was 1.3-1.6 mm, from which PTV margins for IOV can be calculated. Tumor regularity and IOV were significantly correlated, potentially allowing for patient-specific margin calculation.

Keywords: GTV; Interobserver variation (IOV); Liver metastases; MRI; Quality assurance (QA); Tumor delineation.