Comparison of the gross tumor volume in end-expiration/end-inspiration (2 Phase) and summated all phase volume captured in four-dimensional computed tomography in carcinoma lung patients

Purpose: The aim of this study was to compare the delineation and treatment planning of 2 Phase based (end-expiration and end-inspiration) internal gross tumor volume (IGTV) with 10-phase based (four-dimensional [4D]) IGTV. Materials and Methods: Patients with lung tumors at different sites were selected for the study. The location of the tumor in Groups A, B, C were at the upper lobe (attached to the chest wall), middle lobe, and lower lobe, respectively. We contoured the GTV on each of the 10 respiratory phases of the 4D computed tomography (4DCT) data set. The combination of these GTVs produced the IGTV 'All Phases.' GTV was also generated on the extreme respiratory phases. The combination of these two GTVs produced IGTV '2 Phases.' Treatment planning was done, and dose to organs at risks (OARs) were compared in both cases. Results: The average volume of IGTV '2 Phases' and IGTV 'All Phases' for Group A were nearly same. However, for Group B and Group C, IGTV '2 Phases' were smaller than the IGTV 'All Phases.' Lung-GTV doses were less in 'exp-insp' phases than in '4DCT' for Groups B, C, whereas it was same for 'expiration-inspiration' and '4DCT' in Patient A. Conclusion: Patients with tumor upper lobe tumor have no difference in tumor coverage and OARs sparing in the 2 Phase and all phases but middle lobe and lower lobe have a greater excursion during respiration and hence greater all phases IGTV.