Analysis of influential factors for variability in delineation of lumpectomy cavity based on 4DCT in end-exhalation phase

Abstract

Objective To investigate the effects of computed tomography (CT) slice thickness,lumpectomy cavity (LC) volume,cavity visualization score (CVS),and number of metal clips on the interobserver and intraobserver variability in the delineation of LC after breast-conserving surgery based on four-dimensional (4D) CT.Methods Thirty-five patients who had underwent breast-conserving surgery and had at least 5 metal clips placed in the LCs underwent 4DCT scans.For each patient,LC was delineated on the CT images in the T50 (end-exhalation) phase.The patients were stratified according to LC volume,CVS,CT slice thickness,and number of metal clips.Among different patient groups,interobserver and intraobserver variability in LC (Ai and Aintra) and the dice similarity coefficients (DSCs) between LCs (DSCinter and DSCintra) were evaluated and compared.Results LC volume,CVS,number of metal clips,and 4DCT slice thickness were not significantly correlated with △intra and DSCintra (P =0.628,0.842,0.080).There were no significant differences in △inter and DSCinter between the patient groups with 4DCT slice thickness of 2,3,and 5 mm (P =0.211 and 0.727),and there was no correlation between 4DCT slice thickness and Ainter and DSCinter (P =0.414,0.594).LC volume was negatively correlated with Ai (P =0.024);compared with those with LC volumes smaller than the mean value,the patients with LC volumes not smaller than the mean value had a significantly higher DSCinter (P =0.025) and a significantly lower Ainter(P =0.009).The patient group with a CVS of 3-5 had a significantly higher DSCinter than that with a CVS of 1-2(P =0.004),and CVS was positively correlated with DSCinter(P =0.007).There were no significant differences in Ainter and DSCinter between the patient groups with 7-9 and 5-6 metal clips (P =0.159,0.825).Conclusions For the breast cancer patients who have at least 5 metal clips placed at the boundary of LC after breast-conserving surgery,LC volume and CVS are still the main influential factors for variability in LC delineation.More metal clips in addition to 5-6 ones are not helpful for LC delineation. Key words: Breast conserving radiotherapy; Lumpectomy cavity delineation; Tomography, Xray computed,slice thickness; Surgical clip number; Cavity visualization score