Purpose: To assess the variability among clinicians in the delineation of mediastinal and hilar lymph node stations (LNS) according to the published recommendations in the treatment planning of elective nodal irradiation for lung cancer.
Methods: Nine observers delineated on axial CT scans of five cases the LNS according to the guidelines of the published Atlas. Next, the Volumes of Consensus (VC)--fitting strictly the guidelines--for each LNS and case were collectively defined. Volume of Intersection (VI) as the overlap of the Delineated Volume (DV) for each LNS, case and observer with respective VC was computed. The Concordance Index (CI) for respective LNS and observers was defined as "VI/VC x 100%". The Discordance Index (DI) for respective LNS and observers was defined as "(1-VI/VD) x 100%".
Results: Mean values of CI and DI for all observers were 69% and 36%, respectively. For five radiation oncologists who used to work as a team the ways of delineation were similar. The poorest reproducibility was shown for LNS 5, 7, 10R, and 10L.
Conclusions: Although detailed guidelines are used there is still substantial room for improvement. More training in the use of the Atlas is recommended.