Abstract
ObjectiveThis study investigated interobserver and intraobserver variability in radiation oncologists' definition of the tumor bed (TB) after breast-conserving surgery (BCS).ResultsThe 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 (Δinter, DSCinter) in TB delineation, and no significant difference was noted among the three groups. The TB volume was negatively correlated with Δinter. DSCinter improved significantly with increased TB volume and decreased Δinter. DSCinter also increased significantly in patients with a CVS of 3 to 5 compared with patients with a CVS of 1 to 2. DSCinter was thus positively correlated with the CVS, with a correlation coefficient of 0.451. The use of 7 to 9 surgical clips neither decreased Δinter nor increased DSCinter.Materials and MethodsFive 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 (Δinter and Δintra) in different groups were evaluated and compared.ConclusionsInter(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.
Highlights
Developments in radiation therapy delivery after breast-conserving surgery (BCS), such as threedimensional conformal external beam radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT), and image-guided radiation therapy (IGRT), have improved the accuracy of radiation delivery [1,2,3]
No correlation was noted between computed tomography (CT) slice thickness and interobserver variability (Δinter, DSCinter) in tumor bed (TB) delineation, and no significant difference was noted among the three groups
Materials and Methods: Five or more surgical clips were placed at the TB during lumpectomy
Summary
Developments in radiation therapy delivery after breast-conserving surgery (BCS), such as threedimensional conformal external beam radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT), and image-guided radiation therapy (IGRT), have improved the accuracy of radiation delivery [1,2,3]. Whole-breast irradiation (WBI) with or without a tumor bed (TB) boost in combination with BCS remains the standard treatment for early-stage breast cancer. External beam partial breast irradiation (EB-PBI) has recently attracted more attention in this field [4,5,6]. Several issues and unanswered questions remain regarding the use of EB-PBI or WBI with a TB boost after BCS, including inter-fraction breathing motion and intra-fraction set-up variation, which may lead to displacement and deformation of the planning target volume (PTV). Many factors influence TB identification, such as the cavity visualization score (CVS) on computed tomography (CT), the interval from BCS to the CT simulation scan, the number of surgical clips placed during surgery, and breast distortion after surgery [5,6,7,8,9]
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