Definition of internal target volume and domestric study for hepatocellular carcinoma using four-dimensional CT

Abstract

Objective To define individualized internal target volume (ITV) for hepatocellular car-cinoma using four-dimensional (4D) CT, and to compare the differences in target volume definition and dose distribution among 3D, 4D and respiratory-gated plans. Methods 4DCT scanning was obtained for 12 pa-tients with hepatoceUular. Gross tumor volume (GTV), clnical target volume (CTV) and normal tissues were contoured on all 10 respiratory phases of 4DCT images. The 3D, 4D and gated treatment plans were prepared for each patient using three 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);3) PTVGatingwas derived from ITVGating, which encompassed 3 CTVs within ga-ting-window at end-expiration plus SMs. The PTV volume and dose distribution were compared among differ-ent plans. Results The PTV3D was the largest in all 12 patients, but still missed partial target volume in 5 patients when comparing with PTV4D. Both the 4D plans and the gated plans spared more normal tissues than the 3D plans, especially the hver. Without increasing normal tissue dose, the 4D plans allowed for increas-ing the calculated dose from (50.8±2.0) Gy (3D plans) to (54.7±3.3) Gy, and the gated plans could further increase the dose to (58.0±3.9) Gy. Conclusions The 4DCT-based plans can ensure optimal tar-get coverage with less irradiation of normal tissues and allow dose escalation when compared with 3D plans.Respiratory gated radiotherapy can further reduce the target volumes to spare more surrounding tissues, espe-cially for patients with large extent of respiratory mobility. Key words: Liver neoplasm/radiotherapy; Radiotherapy,three-dimensional conformal; Tomo-graphy,X-ray computed, four-dimensional; Dosimetry