Comparison of Magnetic Resonance Imaging and Computed Tomography–Based Volume Delineation of Lumpectomy Cavity Without Surgical Clips in Breast-Conserving Radiotherapy

Abstract

First, to compare magnetic resonance (MR) imaging and computed tomography (CT) -based definition of lumpectomy cavity in patients without surgical clips. Second, to quantify consistency of MR and CT-based lumpectomy cavity delineation for breast-conserving radiotherapy. Between August 2018 and March 2019, twenty patients with T1-2N0M0 breast cancer at our institution were enrolled in this study. All the patients had been treated by breast-conserving surgery without implantation of surgical clips, and prepared to receive radiotherapy. MR and CT images were required in the same day for each patient. Three radiation oncologists independently assigned cavity visualization score (CVS), and delineated the lumpectomy cavity based on CT then on MR images with a 14-day interval for each patient. Interobserver variability was assessed by volumes, generalized conformity index (CIgen) and the distance between the centers of mass (dCOM). Differences in means were tested by the paired sample t-test or One-way analysis of variance, as appropriate. The median age of included patients was 48 years old (range, 33-73). Mean volumes of lumpectomy cavity derived from MR were 22%, 27% and 21% smaller than those based on CT images for each radiation oncologist. And mean CVS was 2.43±0.92 and 3.23±1.34 for CT and MR scans (P = 0.035). In addition, mean CIgen was significantly superior and dCOM was closer for MR when compared to CT (CIgen: 0.59 vs 0.52, P = 0.008; dCOM: 1.30 cm vs 1.39 cm, P = 0.095). In the subgroup with a CVS≥3, the mean dCOM was also obviously larger obtained from CT than those from the MR images (1.35 cm vs 1.19 cm, P = 0.048). A positive association was observed between CVS and CIgen for CT and MR, while CVS was negatively correlated with dCOM for MR images (both P <0.001). In the present study, when compared to CT, MR was able to improve the visualization of postoperative lumpectomy cavity changes. In addition, MR yielded a more precise definition of lumpectomy cavity and improved the consistency of lumpectomy cavity delineation in patients without the aid of surgical clips.