应用锥形束CT分析肿瘤放疗中分次间及分次内摆位误差

Interfractional and Intrafractional Setup Errors in Radiotherapy for Tumors Analyzed by Cone-beam Computed Tomography

背景与目的:放射治疗中肿瘤患者每次的治疗摆位受很多因素影响,存在分次间及分次内摆位误差,本研究目的是采用锥形束CT(cone-beam computed tomography,CBCT)影像技术研究肿瘤患者放射治疗中摆位误差及纠正方法。方法:对51例放疗肿瘤患者,其中头颈部肿瘤19例,胸部肿瘤25例,腹、盆部肿瘤7例,在每次照射前首次摆位后、摆位误差调整后及治疗结束时获取CBCT,通过系统的匹配功能,将获取的CBCT图像和计划CT图像匹配,获得左右(X)、头脚(Y)、前后(Z)3个方向的摆位误差。分析摆位误差及纠正方法。结果:51例患者共进行CBCT扫描1934次。每次治疗开始前首次摆位CBCT955次,调整治疗床后再次CBCT扫描525次,治疗后CBCT扫描454次。X、Y、Z三维方向分次间摆位误差在头颈部分别为(1.2±0.9)mm、(1.2±1.1)mm和(1.0±0.8)mm;在胸部分别为(2.3±1.9)mm、(4.2±3.7)mm和(2.4±2.1)mm;在腹、盆部分别为(1.7±1.5)mm、(4.7±3.6)mm和(2.1±1.6)mm。和调整后比较,头颈部肿瘤治疗后摆位误差在三维方向均有增加,并且差异均有显著性(P<0.05);而体部肿瘤这种差异在X、Y、Z3个方向均无显著性(P>0.05)。结论:每次治疗前通过CBCT获得分次间摆位误差并对其进行纠正对提高放射治疗精度有积极意义。分次内误差在头颈部肿瘤治疗过程中变化明显,这在设计治疗计划时应予以考虑。胸部及腹、盆部分次内误差还有待于进一步研究。

BACKGROUND ＆ OBJECTIVE Both interfractional and intrafractional setup errors may affect the precision of radiotherapy. This study was to analyze the interfractional and intrafractional setup errors in radiotherapy for tumors using cone-beam computed tomography （CBCT）. METHODS Of the 51 patients received radiotherapy, 19 had head and neck tumors, 25 had thoracic tumors, and seven had abdominal-pelvic tumors. Patients received CBCT scans after initial setup, after re-positioning and after radiation delivery. The CBCT images were registered to the planning CT images, and setup errors on X,Y, Z axes were analyzed. RESULTS.. A total of 1 934 CBCT scans were performed on 51 patients, of which 955 were performed after initial setup, 525 after re-positioning and 454 after radiation delivery. The interfractional setup errors on X, Y and Z axes were （1.2±0.9） mm, （1.2±1.1） mm and （1.0±0.8） mm, respectively, for head and neck tumors; （2.3±1.9） mm, （4.2±3.7） mm and （2.4±2.1） mm, respectively, for thoracic tumors; （1.7±1.5） mm, （4.7±3.6） mm and （2.1 ±1.6） mm, respectively, for abdominal-pelvic tumors. Comparing with the post-correction position, the post-treatment setup errors in head and neck tumors increased significantly on all three axes （P〈0.05）, whereas the difference was not significant in trunk tumors （P〉0.05）. CONCLUSIONS： Measurement and correction of interfractional setup errors before each fraction using CBCT could help to improve the precision of radiotherapy. The intrafractional setup error variations are obvious in head and neck tumors and should be taken into account during treatment planning. The intrafractionat setup errors in trunk tumors need further study.