Analysis of the variability among radiation oncologists in delineation of the postsurgical tumor bed based on 4D-CT

Abstract

Objective: This study investigated interobserver and intraobserver variability in radiation oncologists’ definition of the tumor bed (TB) after breast-conserving surgery (BCS).

Results: The TB volume, CVS and number of surgical clips were not significantly related to intraobserver variability. Moreover, no correlation was noted between CT slice thickness and interobserver variability (Δ_inter, DSC_inter) in TB delineation, and no significant difference was noted among the three groups. The TB volume was negatively correlated with Δ_inter. DSC_inter improved significantly with increased TB volume and decreased Δ_inter. DSC_inter also increased significantly in patients with a CVS of 3 to 5 compared with patients with a CVS of 1 to 2. DSC_inter was thus positively correlated with the CVS, with a correlation coefficient of 0.451. The use of 7 to 9 surgical clips neither decreased Δ_inter nor increased DSC_inter.

Materials and Methods: Five or more surgical clips were placed at the TB during lumpectomy. The TB was delineated on the end expiration scan. The data were stratified based on the cavity visualization score (CVS), CT slice thickness and surgical clip number. The Dice similarity coefficient (DSC) and inter(intra)observer variability (Δ_inter and Δ_intra) in different groups were evaluated and compared.

Conclusions: Inter(intra)observer variability in TB delineation was decreased for breast cancer patients implanted with 5 or more surgical clips in the cohort with a higher CVS and a larger TB. The use of more than 6 surgical clips did not significantly improve TB delineation, so 5 to 6 surgical clips are likely adequate to delineate the TB.