Send to

Choose Destination
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

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



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.


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).


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.


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.


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

Supplemental Content

Full text links

Icon for PubMed Central
Loading ...
Support Center