Defining internal target volume (ITV) for hepatocellular carcinoma using four-dimensional CT

Background and purposeTo define individualized internal target volume (ITV) for hepatocellular carcinoma using four-dimensional computed tomography (4DCT).Materials and methodsGross tumor volumes (GTVs) and clinical target volumes (CTVs) were contoured on all 10 respiratory phases of 4DCT scans in 10 patients with hepatocellular carcinoma. The 3D and 4D treatment plans were performed for each patient using two different planning target volumes (PTVs): (1) PTV3D was derived from a single CTV plus conventional margins; (2) PTV4D was derived from ITV4D, which encompassed all 10 CTVs plus setup margins (SMs). The volumes of PTVs and dose distribution were compared between the two plans.ResultsThe average PTV volume of the 4D plans (328.4 ± 152.2 cm3) was less than 3D plans (407.0 ± 165.6 cm3). The 4D plans spared more surrounding normal tissues than 3D plans, especially normal liver. Compared with 3D plans, the mean dose to normal liver (MDTNL) decreased from 22.7 to 20.3 Gy. Without increasing the normal tissue complication probability (NTCP), the 4D plans allowed for increasing the calculated dose from 50.4 ± 1.3 to 54.2 ± 2.6 Gy, an average increase of 7.5% (range 4.0–16.0%).ConclusionsThe conventional 3D plans can result in geometric miss and include excess normal tissues. The 4DCT-based plans can reduce the target volumes to spare more normal tissues and allow dose escalation compared with 3D plans.