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

Abstract

Background and purpose To define individualized internal target volume (ITV) for hepatocellular carcinoma using four-dimensional computed tomography (4DCT). Materials and methods Gross 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) PTV 3D was derived from a single CTV plus conventional margins; (2) PTV 4D was derived from ITV 4D, which encompassed all 10 CTVs plus setup margins (SMs). The volumes of PTVs and dose distribution were compared between the two plans. Results The average PTV volume of the 4D plans (328.4 ± 152.2 cm 3) was less than 3D plans (407.0 ± 165.6 cm 3). 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%). Conclusions The 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.