不同体型盆腔肿瘤患者放疗摆位误差

Set-up errors in radiation therapy for pelvic tumor patients of different somatotypes

目的:采用Elekta iView GT验证系统,测定不同体型的盆腔肿瘤患者行放疗时在三维空间各方向上的系统误差及随机误差,为计划靶区(PTV)和计划危及器官体积(PRV)的制订提供个体化的数学依据。方法:盆腔肿瘤患者30例,采用体膜固定,按照体质指数(BMI)将患者分为4个不同体型。采用前后野和两侧野的电子射野影像装置(EPID)进行位置验证,骨性标志与数字重建图像(DRR)比较,分析分次治疗间摆位误差及分次治疗中器官位置在左右、腹背、头足3个方向上的移动,从而计算出三维空间总的摆位误差,可求出不同体型放疗PTV和PRV所需的安全边界,同时观察各组在各个方向上移动幅度的发生频率。结果:不同体型的盆腔肿瘤患者,消瘦型、中间型、超重型和肥胖型的分次照射间的摆位误差在左右方向分别为1.8、1.8、2.2、2.7 mm;在腹背方向分别为2.2、1.8、3.6、2.8 mm;头足方向分别为2.4、2.1、2.7、2.6 mm。分次照射中的器官移动误差在左右方向分别为1.9、1.9、2.3、2.5 mm;在腹背方向分别为2.1、2.2、2.9、3.0 mm;头足方向分别为1.8、1.9、2.2、2.5 mm。结论:在盆腔肿瘤患者放疗中,PTV和PRV的制订应遵循个体化的原则,根据患者体型在各方向上采用不同的外放边界。

Objective： The purpose of this study was to quantitatively assess the systematic and random errors in radiation therapy for pelvic tumor patients of different somatotypes and seek an individualized mathematic basis for defining the planning target volume（PTV） and planning organ at risk volume（PRV） in 3 dimensional space.Methods： Thirty patients with pelvic tumor were immobilized by thermoplastic body mask in a spine position and divided into four somatotypes according to their body mass indexes（BMI）.CT simulations were performed and digitally reconstructed radiographs（DRR） were generated as the reference image.To define the appropriate PTV-and PRV-margins for intensity modulation radiated therapy（IMRT）,inter-fractional set-up errors and intra-fractional organ motions were quantitatively evaluated in the right-left（R-L）,anterior-posterior（A-P） and cranial-caudal（C-C） directions.And the frequency of shift in the three directions were observed.Results： For the pelvic tumor patients with different BMIs,the inter-fractional set-up errors of the emaciated,moderate,overweight and obese somatotypes were 1.8,1.8,2.2 and 2.7 mm in the R-L direction,2.2,1.8,3.6 and 2.8 mm in the A-P direction,and 2.4,2.1,2.7 and 2.6 mm in the C-C direction.The intra-fractional organ motions of the four somatotypes were 1.9,1.9,2.3 and 2.5 mm in the R-L,2.1,2.2,2.9 and 3.0 mm in the A-P,and 1.8,1.9,2.2 and 2.5 mm in the C-C direction.Conclusion： In the pelvic irradiation,the definition of PTV and PRV should be individualized.