Comparison of internal target volumes for hepatocellular carcinoma defined using 3DCT with active breathing coordinator and 4DCT.

The aim of this paper is to study the feasibility for determining the individual internal target volume (ITV) for hepatocellular carcinoma (HCC) using 3DCT associated with active breathing coordinator (ABC), comparing the ITVs defined by 3DCT associated with ABC and 4DCT. Thirteen patients with HCC after transarterial chemoembolization (TACE) treatment underwent 4DCT simulation and 3DCT simulation associated with ABC in free breathing (FB), end inspiration hold (EIH) and end expiration hold (EEH). The 4DCT images were sorted into 10 phases according to the respiratory cycle and labeled as CT(0), CT(10)...CT(90); and CT(MIP) (the maximum intensity projection image) was reconstructed. GTV(0), GTV(10)...GTV(90), GTV(MIP) on 4DCT, and the GTV(FB), GTV(EIH), GTV(EEH) on 3DCT were contoured. GTV(0,10...90), GTV(0) and GTV(50), GTV(EIH) and GTV(EEH) were merged into ITV(1), ITV(2) and ITV(3). The individual margins from GTV(FB) to ITV(1-3) were obtained and applied to ITV(FB) (labeled as ITV(FB-1), ITV(FB-2), ITV(FB-3)), respectively. All the target volumes were normalized by ITV(1). The volume of GTVs, ITVs and the margins were compared. There was no significant difference of diaphragm mobility between 4DCT and 3DCT (P > 0.05), nor significant difference among the volume of the GTVs. The three ITVs were larger than the GTV(MIP) (P < 0.05), but there was no significant difference among three ITVs. It's similar to the differences both in the margins of three dimensions from GTV(FB) to ITV(1-3) and in the volumes among ITV(FB-1), ITV(FB-2) and ITV(FB-3) (P > 0.05). This study shows that it's safe and feasible to determine the individual ITV for HCC using 3DCT associated with ABC in comparison with 4DCT.