Position and volume of related anatomical structures between quiet end-inspiration and end-expiration three dimensional CT assisted with active breathing control and corresponding phases in four dimensional CT

OBJECTIVE:To compare the position and/or volume of diaphragm dome,lung and heart between quiet end-inspiration and end-expiration three dimensional CT(3DCT)assisted with active breathing control(ABC)and the corresponding phases in four dimensional CT(4DCT).METHODS:Fifteen patients with peripheral lung cancer received radiotherapy in Shandong Cancer Hospital from Aug.3,2011to Dec.12,2011underwent 4DCT simulation scan during free breathing and 3D-CT simulation scans in end-inspiratory hold(CTEIH)and end-expiratory hold(CTEEH)in succession.The 4DCT images from each respiratory cycle were sorted into 10phases:the 0phase was defined as end-inspiratory phase(CT0),while the 50% phase was defined as end-expiratory phase(CT50).The left and right lungs,heart,and both diaphragm domes were delineated separately on CT0,CT50,CTEIHand CTEEHimages.RESULTS:In the cranio-caudal direction,between CTEIHand CTEEH,CT0and CT50,the mean displacement differences of both diaphragm domes were not larger than 1.5mm and were not statistically significant(Zranged from-1.62to-1.21,Pranged from 0.106to 0.228).Between CTEIHand CT0,CTEEHand CT50,the centroid position differences of two lungs and heart were found all statistically significant(Zranged from-3.27to-1.93,Pranged from 0.001to 0.047)in the cranio-caudal direction,and not statistically significant(Zranged from-0.26to-1.58,Pranged from 0.128to 0.798)in the radial directions.The volumes of two lungs were both larger in CTEIHand CTEEHthan in CT0and CT50,and the differences between them were found both statistically significant(t=-5.07,-2.25;P=0.000,0.041),while the volume of heart was larger in CT0and CT50 than in CTEIHand CTEEH,but the differences between them were found both no statistical significace(t=2.10,1.85;P= 0.054,0.085).CONCLUSION:From the point of view of the lung and heart protection,when other conditions are same, gated radiotherapy in quiet end inspiration is better basing on ABC than basing on 4DCT.