Feasibility of delineation internal target volumes of lung cancer using four-dimensional cone-beam CT

Abstract

Objective To study the feasibility of contouring internal target volumes of lung cancer using four-dimensional cone-beam CT(4D-CBCT). Methods Twenty-four cases of lung cancer coming from Nanjing Medical University First Affiliated Hospital were selected with simple random sampling. Locating CT images were obtained with simulating CT under quiet breathing, and the mid-position image of 4D-CBCT were obtained in the first fraction, three-dimensional cone-beam CT(3D-CBCT) were obtained by changing image reconstruction algorithm from four-dimensional to three-dimensional. Register the planning images using the bone registration. GTVs were contoured respectively based on CT, mid-position image of 4D-CBCT and 3D-CBCT. CTVCT, ITV4D and ITV3D were defined with a margin of 7 mm accounting for microscopic disease. ITVCT were defined based on CTVCT with an isotropic internal margin of 5 mm. The differences in the position, volume, Dice's similarity coefficient (DSC) and inclusion relationship of different volumes were compared. Results In the direction of CC, the differences between ITVCT and ITV3D for the middle-lower lobe had statistical significance in the center of target location (Z=-2.027, P 0.05). The mean of DSC between ITVCT and ITV3D was less than 75%, while the one between ITV4D and ITV3D was more than 90% (Z=-2.940, -2.975, P<0.05). The mean percentages of ITVCT and ITV4D excluding ITV3D were approximately 40% and 5% respectively (Z=-2.952, -3.185, P<0.05). Conclusions The volume of internal target volumes of lung cancer can be reduced using the mid-position image of 4D-CBCT, which might provide an alternative of individualized adaptive radiotherapy for lung cancer. Key words: Lung Cancer; Four-dimensional; Internal target volume; Cone beam CT; Delineation target area