影像引导下放射治疗脊柱肿瘤六自由度摆位误差分析

目的:探讨颈椎、胸椎及腰椎肿瘤在锥形束CT( cone beam CT,CBCT)影像引导下的调强放射治疗( image guided radiation therapy, IGRT)六自由度摆位误差分析. 方法:收集2013年5月至2014年6月在北京大学第三医院行脊柱恶性肿瘤放疗的患者30 例,其中颈椎肿瘤10 例,胸椎肿瘤10 例,腰椎肿瘤10 例. 采用瑞典医科达( ELEKTA)公司AXESSE直线加速器CBCT引导,用HexaPODTM evoRT床从平移和旋转六自由度方向在线校正摆位误差,CT模拟定位获取治疗计划参考图像(层厚3 mm,120 kV,200 mAs). 每次治疗前行千伏级( kV级) CBCT扫描(100 kV,36. 6 mAs,s20射野准直器),CBCT图像采用骨窗模式与计划参考图像自动匹配,并经高资质医师和物理师共同确认,误差校正后再次行CBCT扫描,将两次图像与计划参考图像分别进行匹配验证. 本研究共收集838次摆位校正前、后匹配结果,分别记录患者平移摆位误差左右方向X( lateral)、进出方向Y( lngitudinal)、升降方向Z(vertical)、旋转误差俯仰方向RX(pitch)、滚动方向RY(roll)及左右旋转方向RZ(yaw)匹配结果. 应用SPSS 13. 0统计软件,对HexaPODTM evoRT床校正前后位移误差数据行配对t检验. 结果:椎体肿瘤摆位误差(绝对值)中,3个平移X、Y和Z方向摆位误差结果分别为颈椎(1.71 ±0.10)mm、(1.81 ±0.11)mm和(1.94 ±0.09)mm;胸椎(3.17 ±0.19)mm、(4.26 ±0.28)mm和(2.18 ±0.12)mm;腰椎(2.69 ±0.24)mm、(3.33 ±0.26)mm和(2.86 ± 0. 21)mm. 患者摆位后首次CBCT获得摆位误差数据与误差纠正后(动床后)再次CBCT验证后获得残余误差数据3个平移X、Y和Z方向分别为颈椎(0. 5 ± 2. 4) mm、(0. 01 ± 2. 4) mm和(2. 4 ± 1. 4) mm,胸椎(1. 17 ± 0. 11) mm、(0.26 ±0.30)mm和(0.08 ±0.12)mm,腰椎(1.09 ±0.24)mm、(2.03 ±1.26)mm和(0.06 ±0.51)mm. 进行配对t检验结果:颈椎及胸椎平移3个方向误差纠正前后差异均有统计学意义;腰椎仅是升降Z方向平移误差纠正前后差异统计学有意义(t= -3. 518,P<0. 001). 3个旋转RX、RY和RZ方向摆位误差分别为颈椎肿瘤0. 67° ± 0. 04°、1. 06° ± 0. 06°和0. 78° ± 0. 05°,胸椎0. 62° ± 0. 05°、0. 75° ± 0. 06°和0. 84° ± 0. 06°,腰椎0. 59° ± 0. 06°、0. 80° ± 0. 07°和0. 73° ± 0. 06°;误差纠正后(动床后)再次CBCT验证后获得残余误差数据3个旋转方向RX、RY和RZ方向分别为颈椎肿瘤0. 27° ± 0. 14°、1. 20° ± 0. 04°和0. 28° ± 0. 05°,胸椎0. 02° ± 0. 20°、 0. 05° ± 0. 26°和0. 64° ± 0. 16°,腰椎0. 09° ± 0. 26°、0. 50° ± 0. 05°和0. 03° ± 0. 16°,误差纠正前后颈椎和腰椎旋转3个方向差异均具有统计学意义,胸椎仅是滚动方向RY方向差异有统计学意义(t=7. 106,P<0. 001). 30例患者疼痛均有缓解,未发现放疗副反应. 结论:IGRT下HexaPODTM evoRT床对脊柱肿瘤放射治疗的摆位误差纠正有明显作用,建议采用在线校正脊柱肿瘤放射治疗摆位误差.

Errors in six degree-of-freedom pose estimation of spine tumors assessed by image guided radiotherapy

Objective:To evaluate the six-degree setup errors of tumors of cervical vertebra, thoracic vertebra and lumbar vertebra by image guided radiotherapy. Methods:From May 2013 to June 2014, 30 patients with spinal malignant tumors(10 patients of cervical vertebra, thoracic vertebra and lumbar verte-bra respectively) were treated with Elekata Synergy accelerator(Elekta company,Sweden). Six-degree set up errors were corrected using HexaPODTM evoRT bed under image of on board cone beam computed tomography ( CBCT) guided. All the patients received kilovoltage CBCT before receiving radiotherapy and after correction. The acquired images were co-registered with planning CT with bone window. The data of 838 CT images were analyzed and the errors of translational directions X ( lateral ) , Y ( lngitudi-nal),Z(vertical)and rotational directions RX(pitch), RY(roll), RZ(yaw) were recorded. The data were compared by t-test using SPSS 13. 0. Results:The absolute translational setup errors in X, Y and Z axes of cervical vertebra before correction were (1. 71 ± 0. 10) mm, (1. 81 ± 0. 11) mm and (1. 94 ± 0. 09) mm respectively:(3. 17 ± 0. 19) mm, (4. 26 ± 0. 28) mm and (2. 18 ± 0. 12) mm for thoracic vertebra, and (2. 69 ± 0. 24) mm, (3. 33 ± 0. 26) mm and (2. 86 ± 0. 21) mm for lumbar vertebra. The residual setup errors in X, Y and Z axes of cervical vertebra were (0. 5 ± 2. 4) mm,(0. 01 ± 2. 4) mm and (2. 4 ± 1. 4) mm, respectively after correction;(1. 17 ± 0. 11) mm,(0. 26 ± 0. 30) mm and (0. 08 ± 0. 12) mm for thoracic vertebra and (1. 09 ± 0. 24) mm,(2. 03 ± 1. 26) mm and (0. 06 ± 0. 51) mm for lumbar vertebra. The t-test of paired data of set up errors before and after CBCT showed significant difference in three translational directions of cervical vertebra and thoracic vertebra, only Z (t= -3. 518,P<0. 001) for lumbar vertebra. The absolute rotational setup errors in RX,RY and RZ axes of cervical vertebra before correction were 0 . 67 ° ± 0 . 04 ° ,1 . 06 ° ± 0 . 06 ° and 0 . 78 ° ± 0 . 05 ° respec-tively. 0. 62° ± 0. 05°, 0. 75° ± 0. 06°, and 0. 84° ± 0. 06° for thoracic vertebra, 0. 59° ± 0. 06°, 0. 80° ± 0. 07°, and 0. 73° ± 0. 06°for lumbar vertebra. The rotational directions RX, RY and RZ axes of cervical vertebra were 0 . 27 ° ± 0 . 14 ° , 1 . 20 ° ± 0 . 04 ° and 0 . 28 ° ± 0 . 05 ° respectively;0 . 02 ° ± 0 . 20 ° , 0. 05° ± 0. 26°and 0. 64° ± 0. 16°for thoracic vertebra and 0. 09° ± 0. 26°, 0. 50° ± 0. 05°,and 0. 03° ± 0. 16°for lumbar vertebra. The t-test of paired data of set up errors before and after CBCT showed signifi-cant difference in three rotational directions of cervical vertebra and lumbar vertebra, only RY(t=7. 106, P<0. 001)for thoracic vertebra. All the patients acquired pain relief and there was no radiation-induced toxicity detected clinically during a median follow-up of 6 months. Conclusion:Six-degree set up errors of spine tumors were corrected effectively with HexaPODTM evoRT bed under CBCT image guided and its feasibility in day-to-day clinical practice has been demonstrated.