Abstract P5-14-17: Post-lumpectomy tumorbed delineation for breast boost or partial breast irradiation: The influence of additional MRI and CT imaging

Abstract

Abstract Rationale/Purpose In early stage breast cancer patients, most recurrences occur in the vicinity of the original tumor location. Therefore, after initial lumpectomy it is important to accurately delineate the tumorbed (TB) area for breast boost and partial breast irradiation on the planning-CT scan. However, consistency in TB delineation among radiation oncologists is low on standard CT imaging. The purpose of this study was to determine whether additional pre- and postoperative MRI and CT imaging could increase consistency in standard CT-guided target volume delineation among radiation oncologists. Methods Fourteen cT1-2 patients underwent MRI and CT imaging in supine radiotherapy position before and after lumpectomy. TBs were delineated by 4 breast radiation oncologists following delineation guidelines on the standard postoperative planning-CT alone, and planning-CT registered to 1) postoperative MRI (T1 (with and without fat suppression) and T2 weighted sequences) 2) preoperative contrast-enhanced (CE) CT, and 3) preoperative CE-MRI (T1 weighted sequence with fat suppression). Consistency was defined by the conformity index (CI), which was calculated by dividing the encompassing volume of each observer pair, by the volume of overlap for each observer pair. Furthermore, volumes and the distance between centres of mass (dCOM) of the delineated TBs were determined. A Wilcoxon signed-rank test was performed to compare variables between different imaging modalities, with a significance level of a = 0.05. Results Results of the analysis are shown in Table 1. Addition of a postoperative MRI to the standard postoperative planning CT did not influence the CI (p = 0.176) or dCOM (p = 0.110). However, the TB volumes increased significantly with a median increase of 6 cm3 (p<0.001). Addition of a preoperative CT or MRI increased the CI by 0.01 and 0.02 (both p<0.001). Furthermore, preoperative CT and MRI increased dCOM (p = 0.004 and p = 0.001) and volumes (both p<0.001). Table 1 medianrange p-valueVolume (cm3) CT224-934 CT + postoperative MRI283-964<0.001CT + preoperative CT266-933<0.001CT + preoperative MRI257-933<0.001 Conformity index CT0.570.00-0.90 CT + postoperative MRI0.610.00-0.890.176CT + preoperative CT0.580.00-0.90<0.001CT + preoperative MRI0.590.00-0.89<0.001 dCOM (mm) CT50-53 CT + postoperative MRI40-520.110CT + preoperative CT31-420.004CT + preoperative MRI50-480.001 Conclusion Although significant, the addition of postoperative MRI, preoperative CE-CT or preoperative CE-MRI did not result in a clinically relevant improvement of the consistency in postoperative CT-guided TB delineation among radiation oncologists. Furthermore, target volumes increased with all imaging modalities. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-14-17.