Comparison Of Rectal Cancer Tumor Volume Parameters Measured On MRI Sequences And CT With Those On Pathological Sepcimen

Objective:To compare gross tumor volume?GTV?parameters measured on MRI sequences?T1WI,T2WI,DWI?and/or CT with those on pathological specimen with rectal cancer for assessing GTV delineation accuracy based on MRIs and CT.Methods:Twenty two patients with stage cT1-4aN-/+M0 rectal cancer were prospectively enrolled.MRI sequences including T1WI,T2WI and DWI,and/or CT of the pelvis were performed before operation.Volume parameters such as tumor length along the rectal axis(L_T1-L,L_T2-L,L_DWI-L,L_CT-L),Maximum tumor width perpendicular to rectal axis(L_T1-W,L_T2-W,L_DWI-W,L_CT-W)and tumor actual area in that perpendicular plane(A_T1,A_T2,A_DWI,A_CT)were measured on T1WI,T2WI,DWI and CT respectively for each patient.The respective pathological parameters(L_path-L,L_path-W and A_path)were also measured on surgical specimen after total mesorectal excision.Those two kinds of parameter values measured on imaging and pathology were statistically compared and accuracy appraisal was performed with pathological parameters as“gold standard”.Results:The mean L_path-L was 4.06±1.14 cm,The mean L_T1-L,L_T2-L,L_DWI-L and L_CT-L were 3.91±1.51,4.62±1.41,3.39±1.05 and 3.94±1.23 cm respectively.The correlation coefficients were 0.688,0.635,0.688 and 0.720?P<0.05?.Bland-Altman analysis shows that there was an average 6 mm overestimation on T2WI,and 1mm to 6 mm underestimation on T1WI,DWI and CT in length values compared with those measured on surgical specimen.The mean L_path-W was 2.56±0.94 cm.The mean L_T1-W,L_T2-W,L_DWI-W and L_CT-W were 3.62±0.99,3.66±0.76,3.23±0.58 and 3.64±1.04 cm respectively.The magnitude of mean overestimation ranged from 5.1mm to 11.1 mm.The A_path was4.30±2.83 cm².The A_T1,A_T2,A_DWI and A_CT were 8.98±3.90,8.99±3.43,8.41±3.09 and 9.63±4.40 cm² respectively,and which double overestimated tumor area in the perpendicular rectal plane.Conclusions:With rectal cancer volume parameters measured on surgical specimen as the“gold standard”for comparison,T1WI,DWI and CT tended to underestimate and T2WI overestimate longitudinal length of rectal cancer within the magnitude of 6 mm.The mean maximum width measured on MRIs and CT overestimated horizontal tumor width in the range of 5.1 to 11.1mm,and the tumor areas in the horizontal plane were double overestimated.The findings in this study implies that GTV delineation based on MRI or CT for rectal cancer“boost”preoperative radiotherapy should be conservative lateral to rectum,and longitudianl slice extension was not necessary considering mixed results of the magnitude of under or over tumor length estimation and scan thickness.