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J Radiat Oncol. 2016 Mar;5(1):55-61. Epub 2015 Nov 3.

Quantitative assessment of target delineation variability for thymic cancers: Agreement evaluation of a prospective segmentation challenge.

Author information

1
Division of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas.
2
Department of Radiology, Massachusetts General Hospital, Boston, MA.
3
Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY.
4
Department of Radiation Oncology, The University of Texas Health Science Center San Antonio, San Antonio, TX.
5
Department of Radiation Oncology, University Medical Center, Amsterdam, The Netherlands.
6
Department of Therapeutic Radiology, Yale Cancer Center, New Haven, CT.
7
Department of Radiation Oncology, Kaiser Permanente Southern California, Los Angeles, CA.
8
Department of Radiation Medicine, Oregon Health and Science University Knight Cancer Center, Portland, OR.

Abstract

OBJECTIVES:

We sought to quantitatively determine the inter-observer variability of expert radiotherapy target-volume delineation for thymic cancers, as part of a larger effort to develop an expert-consensus contouring atlas.

METHODS:

A pilot dataset was created consisting of a standardized case presentation with pre- and post-operative DICOM CT image sets from a single patient with Masaoka-Koga Stage III thymoma. Expert thoracic radiation oncologists delineated tumor targets on the pre- and post-operative scans as they would for a definitive and adjuvant case, respectively. Respondents completed a survey including recommended dose prescription and target volume margins for definitive and post-operative scenarios. Inter-observer variability was analyzed quantitatively with Warfield's simultaneous truth, performance level estimation (STAPLE) algorithm and Dice similarity coefficient (DSC).

RESULTS:

Seven users completed contouring for definitive and adjuvant cases; of these, 5 completed online surveys. Segmentation performance was assessed, with high mean±SD STAPLE-estimated segmentation sensitivity for definitive case GTV and CTV at 0.77 and 0.80, respectively, and post-operative CTV sensitivity of 0.55; all volumes had specificity of ≥0.99. Inter-observer agreement was markedly higher for the definitive target volumes, with mean±SD DSC of 0.88±0.03 and 0.89±0.04 for GTV and CTV respectively, compared to post-op CTV DSC of 0.69±0.06 (Kruskal-Wallis p<0.01.

CONCLUSION:

Expert agreement for definitive case volumes was exceptionally high, though significantly lower agreement was noted post-operatively. Technique and dose prescription between experts was substantively consistent, and these preliminary results will be utilized to create an expert-consensus contouring atlas to aid the non-expert radiation oncologist in the planning of these challenging, rare tumors.

KEYWORDS:

Radiotherapy; consensus guidelines; target delineation; thymic carcinoma; thymoma; treatment planning

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