Gross Tumor Volume Contouring Variations in Radiation Therapy of Non-Small Cell Lung Cancer

Accurate delineation of gross tumor volume (GTV) is utmost important for precision radiation therapy and quality ensure of GTV compliance with the protocol definition is essential for multi-center clinical trials. This work aimed to exam GTV delineation by multicenter experts and quantifies the differences in the same one patient with stage III non-small cell lung cancer (NSCLC). The eligible investigators/Centers were physically participated clinical trial training workshop/Global Collaborative Oncology Group (GCOG) semiannual meeting help on December 19, 2020, and those provided personal information to GCOG and submitted the contoured structures to data collection center provided by the meeting sponsor (Varian Med. Inc). The participating experts were provided with the same de-identified cases of stage III NSCLC) and instructions of contouring and plan assessment according to RTOG1106. The reference contours of CT based gross tumor volume (GTV) and PET based metabolic tumor volume (MTV) were delineated by the PI of RTOG1106 and the leading author of the RTOG lung Target atlas. The differences between contours from the participating MD investigators and the PI of RTOG1106 were evaluated by the dice similarity coefficient (DSC). Pre- and post-workshop performance will be compared. A total of 35 centers participated the workshop, 29 of them with completed GTV structures were eligible for this DSC analysis. As shown on the table, the mean DSC of the GTV was 0.87 (range 0.64-0.93). The DSC of 9 hospitals was greater than 0.90, 15 hospitals were between 0.85 and 0.90, 2 hospitals were between 0.80 and 0.85, 2 hospitals were between 0.70 and 0.80, and 1 hospital was between 0.60 and 0.70. Variations were discussed and consensus contours were generated. Of 3 centers submitted post-workshop, the DSC improved by an average of 1%. Variations of CT GTV and metabolic tumor volumes of primary tumor and nodal diseases pre and at mid-treatment as well as changes after workshop will be presented at the meeting. Mid-treatment MTV variations as well as changes in the tumor target volume will be reported at the meeting. Despite of being given the atlas, this study demonstrated more than 10% GTV variations from the reference GTV in 20/29 centers, suggesting an urgent need of training workshop on this topic. GCOG is in the process of generating a consensus target delineation guideline by meticulous analysis of the variations and extensive discussion of representative international experts in NSCLC, aiming to provide a reproducible reference for the GTV delineation work multi-center clinical trials.