Full-Thickness Closure in Breast-Conserving Surgery: The Impact on Radiotherapy Target Definition for Boost and Partial Breast Irradiation. A Multimodality Image Evaluation

During breast-conserving surgery (BCS), surgeons increasingly perform full-thickness closure (FTC) to prevent seroma formation. This could potentially impair precision of target definition for boost and accelerated partial breast irradiation (APBI). The purpose of this study was to investigate the precision of target volume definition following BCS with FTC among radiation oncologists, using various imaging modalities. Twenty clinical T1-2N0 patients, scheduled for BCS involving clip placement and FTC, were included in the study. Seven experienced breast radiation oncologists contoured the tumor bed on computed tomography (CT), magnetic resonance imaging (MRI) and fused CT-MRI datasets. A total of 361 observer pairs per image modality were analyzed. A pairwise conformity among the generated contours of the observers and the distance between their centers of mass (dCOM) were calculated. On CT, median conformity was 44 % [interquartile range (IQR) 28-58 %] and median dCOM was 6 mm (IQR 3-9 mm). None of the outcome measures improved when MRI or fused CT-MRI were used. In two patients, superficial closure was performed instead of FTC. In these 14 image sets and 42 observer pairs, median conformity increased to 70 %. Localization of the radiotherapy target after FTC is imprecise, on both CT and MRI. This could potentially lead to a geographical miss in patients at increased risk of local recurrence receiving a radiation boost, or for those receiving APBI. These findings highlight the importance for breast surgeons to clearly demarcate the tumor bed when performing FTC.