| Abstract: |
We sought to quantitatively determine the interobserver 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. Interobserver 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, five 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 a parts per thousand yen0.99. Interobserver 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 nonexpert radiation oncologist in the planning of these challenging, rare tumors. |
