Résumé
Objective To compare the size of the internal target volume (ITV),biological target volume (BTV) and internal biological target volume (IBTV) based on PET-CT and 4DCT for primary nonsmall cell lung cancer (NSCLC),as well as try to apply IBTV in radiotherapy planning.Methods A total of 15 patients with NSCLC were sequentially scanned by an axial enhanced 3DCT,4DCT and 18F-FDG PET-CT in the thoracic region.The gross target volumes (GTVs) of ten phases of 4DCT images were contoured,and ITV was obtained by fusion of ten GTVs.BTV based on PET-CT images was determined by the SUV 2.0.The IBTV was defined by fusion of ITV and BTV.Planning target volumes (PTVs) based on ITV,BTV,and IBTV (PITV,PBTV,PIBTV) were obtained by ITV,BTV and IBTV with a 10-mm expansion respectively.The metrics of PIBTV,PITV and PBTV were compared,and the planning parameters of target volumes and risk organs were evaluated.Results There was no significant difference between ITV and BTV,but there was significant difference between IBTV and ITV and BTV (F=22.533,P ＜ 0.05).To include more than 95％ volume of IBTV,it is necessary to expand the margin of 9.0(6.0,12.0)mm based on BTV or 10.00(7.0,12.0)mm based on ITV.There was no significant difference between the two groups (P ＞ 0.05).Dice's similarity coefficient of BTV and ITV was 0.72(0.54,0.79).The intensity modulated radiotherapy plan based on PBTV can guarantee 85.6％ (80.5％,91.2％) of PITV to reach the prescription dose,compared with 80.2％ (74.4％,87.6％) of PBTV by the plan from PITV.Additionally,the conformity index and homogeneity index were not ideal.The dosimetric parameters of PITV and PBTV in the PIBTV plan were much better than those in PBTV-and PITV plan.Conclusions The radiotherapy plan based on PET-CT or 4DCT could not guarantee a reasonable dose distribution of PTV expanded from ITV or BTV.Thus,using IBTV for radiotherapy is advised.