基于四维CT原发性肝癌内靶体积的确定及剂量学研究

目的 应用四维CT确定原发性肝癌内靶体积(ITV),比较常规三维计划与四维计划、呼吸门控计划的靶区体积及剂量学差异.方法 选择12例肝癌患者,行四维CT扫描,在10个时相的CT图像中分别勾画GTV、CTV和危及器官.根据PTV_(3D)、PTV_(40)、PTV_(Gating)为每例患者分别设计三维计划、四维计划、呼吸门控计划.PIV_(3D)由CTV外扩常规的安全边界得到,PTV_(4D)由10个时相的CTV融合形成的ITV_(40)外扩摆位误差(SM)得到,PTV_(Gating)由呼气末3个时相的CTV融合形成的ITV_(Gating)外扩SM得到.比较3套计划中靶区体积和危及器官剂量学的差异.结果 12例患者PTV_(3D)均显著大于PTV4D及PTV_(Gating),其中5例患者PTV_(3D)较PTV_(4D)遗漏了部分靶区.四维计划、呼吸门控计划中危及器官的受照剂量均较三维计划降低,以肝最为显著.在不增加正常组织受照剂量的前提下,四维计划的处方剂量可由三维计划的(50.8±2.0)Gy提升至(54.7±3.3)Cy,而呼吸门控计划可进一步提升至(58.0±3.9)Gy.结论 应用四维CT可在三维适形放疗基础上缩小肝癌靶区,在保证覆盖肿瘤的同时减少正常组织的受照剂量,并提升靶区剂量;门控放疗可进一步缩小靶区,更有利于保护正常组织,尤其是对于肝呼吸动度较大的病例.

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

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) PTV_(Gating) was derived from ITV_(Gating), 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.