The Comparative Study Of Target Volume Determination Based On Three-dimensional,Four-dimensional,and Cone Beam Computed Tomography For Primary Esophageal Cancer

BackgroundThe oesophagus was regarded as the tumor tissue when the normal oesophageal wall thickness was more than 5mm on three-dimensional computed tomography(3DCT).The normal oesophageal wall thickness was the main reference for the upper and lower boundaries of the tumor on CT images.But the range of normal oesophageal wall thickness on four-dimensional CT(4DCT)and cone beam CT(CBCT)was indeterminate.The motion information incorporated in distinct patterns CT images were also different for primary oesophageal cancer.ObjectiveTo compare the normal oesophageal wall thickness based on 3DCT,4DCT and CBCT to provide a reference for the delineation of oesophageal tumors.And to compare the volumetric and positional difference of the gross tumor volumes(GTV)for primary esophageal cancer based on 3DCT,4DCT and CBCT.Methods3DCT and 4DCT scans were acquired from 50 patients at the time of treatment simulation.CBCT scans were acquired at the first treatment fraction.The outer oesophageal wall was contoured on 3DCT,the maximum intensity projection of 4DCT(4DCTMIP),the end expiration phase of 4DCT(4DCT50)and the CBCT images.The wall thicknesses were measured on each slice and the average thickness of esophageal wall was obtained.Thirty-four patients underwent 3DCT and 4DCT simulation scans before treatment.CBCT scans were acquired at the first treatment fraction.GTV3 D,GTV4D50,internal GTVMIP(IGTVMIP),and internal GTVCBCT(IGTVCBCT)were delineated separately on 3DCT,4DCT50,4DCTMIP,and CBCT datasets,respectively.The GTVs from 10 respiratory phases of the4 DCT were combined to produce IGTV10.The differences in the position,size and inclusion relation of different volumes were compared.ResultsFor the thoracic and the intra-abdominal segments,there were no significantdifferences between R3 DCT and R50,but there were significant differences between R3 DCT and RMIP,and R3 DCT and RCBCT(P < 0.05).For the upper and middle oesophagus,significant differences were found between RCBCT and RMIP(P<0.05).On 3DCT,4DCT(4DCT50 and4DCTMIP)images,the lower oesophageal wall thickness was greater than that of the upper and middle segments(P=0.008~0.041),and the intra-abdominal oesophagus was larger than the thoracic oesophagus(P<0.0010).No significant differences were found among thoracic oesophagus(P=0.088 ~ 0.945)on CBCT images.Independent of the tumor location,significant differences were observed among the volumes [IGTV10 >(IGTVCBCT or IGTVMIP)>(GTV3D or GTV4D50)].Regarding IGTV10 as the standard volume,the underestimations or overestimations between IGTV10 and IGTVCBCT were larger than that of between IGTV10 and IGTVMIP(P=0.000-0.011;P=0.000-0.023).whereas no significant difference was observed between the percentages of IGTV10 not included in IGTVCBCT and GTV10 not included in IGTV3D(P=0.357-0.943).For upper esophageal tumors,GTV4D50/IGTVCBCT negativey correlated to motion vector(r=-0.756,P=0.011).In AP direction,the centroid coordinates of IGTVCBCT significantly differed from the test volumes(GTV3D,GTV4D50,IGTVMIP and IGTV10).For middle esophageal tumors,IGTV10/IGTVCBCT positively correlated to motion vector(r=0.695,P=0.006).The centroid coordinates of IGTVCBCT significantly differed from those of IGTV10(P=0.046)in AP direction.For distal esophageal tumors,the centroid coordinate of IGTVCBCT showed difference to that of IGTVMIP(P=0.042)in LR direction.For both middle and distal esophageal tumors,the degree of associations of IGTV10 outside IGTVCBCT significantly correlated to the motion vector(r=0.540,P=0.046;r=0.678,P=0.031).The mean value of the MIs between IGTVCBCT and the test volumes ranged from 0.65 to 0.72.ConclusionUniform criterion of the determination of normal oesophageal wall thickness could be adopted to delineate the gross target volume on 3DCT and 4DCT50 images for the thoracic oesophagus.However,it need to be cautious about regarding 5 mm as the criteria of normal oesophageal wall thickness to delineate GTV on 4DCTMIP and CBCT images.CBCT encompasses much more motion information than 3DCT and the end expiration phase of4 DCT images,but slightly less than the ten respiratory phases of the 4DCT.CBCT incorporated similar motion information to MIP images.However,the target motion information encompassed in CBCT and MIP images cannot replace each other.