A Comparison Study Between Gross Tumor Volume Defined By Pre-operative MRI,Post-operative Specimen And Planning CT

Objective: To explore the volume differences and the correlations between gross tumor volume(GTV)defined by pre-operative breast MRI,post-operative specimen and lumpectomy cavity based on clips.And to compare the geometric differences in GTV and surgical clips propagated by rigid and deformable registration using a four-dimensional computed tomography(4DCT)image data set for patients after breast-conserving surgery(BCS).Methods: 1.Fifty eligible patients undergoing breast-conserving therapy were recruited.The GTV delineated by MRI was defined as GTVMRI.GTVMRI+1 was formed by adding 1.0 cm margin around GTVMRI.The volume of excised specimen was measured and defined as GTVES.The volume of pathology was calculated and defined as GTVPAT.In planning CT,the volume of tumor bed was delineated using surgical clips and defined as GTVTB.2.The 4DCT data sets of 44 patients who had undergone BCS were acquired.GTV and selected clips were manually delineated on end-inhalation phase(CT0)and end-exhalation phase(CT50)images of 4DCT data sets.Subsequently,the GTV and selected clips from CT0 images were transformed and propagated to CT50 images using rigid image registration(RIR)and deformable image registration(DIR).The geometric differences in GTV and surgical clips from DIR were compared with those of RIR.Results: 1.The median volumes were 0.97 cm3(range 0.01-6.88cm3)for GTVMRI,12.58(range 3.90-34.13)cm3 for GTVMRI+1,0.97(range 0.01-2.36)cm3 for GTVPAT,15.46(range 1.15-70.69)cm3 for GTVES,19.24(range 4.72-54.33)cm3 for GTVTB.There were no significant differences between GTVMRI and GTVPAT,GTVMRI + 1 and GTVES,GTVES and GTVTB(P=0.188,0.07,0.264).Neither GTVES nor GTVTB correlated with GTVMRI(P=0.071,0.378,respectively).Neither GTVES nor GTVTB correlated with GTVMRI+1(P=0.068,0.375,respectively).GTVTB correlated positively with GTVES(r=0.488,P=0.004).2.The mean Dice similarity coefficient(DSC)index was 0.860 ± 0.042 for RIR and 0.870 ± 0.040 for DIR for GTV(P=0.000).The three-dimensional distance to the center of mass(COM)of the GTV from RIR was longer than that from DIR(1.22 mm and 1.10 mm,respectively,P=0.000).Moreover,in the anterior-posterior direction,displacements from RIR were significantly greater than those from DIR for both GTV and selected clips(P=0.000).However,in the left-right and superior-inferior directions,there were no significant displacement differences between RIR and DIR for GTV and the selected clips(all P > 0.050).Conclusions: Without image-guidance,for patients undergoing breast-conserving therapy,when performing lumpectomy based on the scope of palpation,neither the volume of excised specimen nor lumpectomy cavity delineated based on clips correlated significantly with the volume delineated and constructed based on pre-operative MRI.DIR can improve the overlap for GTV registration from CT0 to CT50 images from 4DCT scanning.Furthermore,DIR is superior to RIR in reflecting the displacement of GTV and selected clips in the anterior-posterior direction induced by respiratory movement.