摘要目的 利用锥形束CT(CBCT)在线研究盆腔肿瘤摆位误差的大小,推算CTV与PTV 之间外放的间隙.方法 应用医科达Synergy IGRT加速器治疗12例盆腔肿瘤患者,通过CBCT影像技术获得患者左右(x)、头脚(y)、前后(z)方向线性摆位误差以及分别以x、y、z轴旋转形成相应的u、v、w旋转摆位误差,分析其摆位误差.结果 12例患者共行229次CBCT,x、y、z、u、v、w轴自由度的系统误差±随机误差分别为(0.49±1.18)mm、(-0.11±3.45)mm、(-2.00±1.59)mm、1.14°±0.67°、0.42°±0.94°、-0.32°±0.68°.其中y方向摆位误差最大、z方向次之、x方向摆位误差最小.x、y、z方向的摆位扩边值分别为4.6、12.5、6.2 mm.结论 盆腔肿瘤放疗时不可避免存在一定程度摆位误差,为减少摆位误差影响CTV外放PTV时考虑x方向5 mm、y方向15 mm,z方向10 mm.

abstractsObjective To analyze setup errors for irradiation of pelvic carcinoma by online conebeam CT (CBCT) scanning and to calculate the external margins from clinical target volume (CTV) to planning target volume (PTV) in treatment planning. Methods Twelve patients with rectal or prostate cancer were enrolled in this study. Translational errors (x,y,z) and rotational errors (u,v,w) were obtained by using CBCT in radiotherapy. Results The set-up errors were gathered from 229 sets of CBCT in 12patients. The systemic ± random errors on x,y,z, u,v and w axes were (0.49 ± 1.18) mm, (-0. 11 ±3.45) mm, (-2. 00 ± 1.59) mm, 1.14°±0. 67°, 0. 42°±O. 94°and -0. 32°±±0. 68°, respectively. Setup errors in the left-right, anterior-posterior, and superior-inferior directions were 4. 6 mm, 12. 5 mm, and 6. 2 mm, respectively. Conclusions Set-up errors were unavoidable in pelvic carcinoma irradiation. To minimize the influence of set-up errors, we suggest a PTV margin of 5 mm, 15 mm and 10 mm in the leftright, anterior-posterior and superior-inferior directions, respectively.