锥形束CT在宫颈癌调强放射治疗中摆位误差分析

Analysis of setup error by cone beam computed tomography in intensity modulated radiotherapy for cervical cancer

目的探讨每日锥形束CT(CBCT)技术在纠正宫颈癌放疗人工摆位误差中的应用价值。方法选取接受调强放射治疗(IMRT)的宫颈癌患者18例,每日放疗前均行CBCT扫描,并与计划CT图像骨性匹配,结合手动微调,获得前后(Vrt)、头脚(Lng)、左右(Lat)三个方向的线性摆位误差,摆位误差纠正后再次CBCT扫描,分别记录每次的摆位误差并进行分析。结果 18例患者共行906次CBCT扫描,摆位误差纠正前和纠正后Vrt方向总平均值(M)、系统误差(∑)、随机误差(σ)分别为0.581、4.068、1.160mm和0.049、0.292、0.277mm,Lng方向纠正前后分别为0.789、3.637、2.031mm和0.477、0.391、0.539mm,Lat方向纠正前后分别为-0.375、2.515、1.564mm和0.094、0.109、0.238mm。摆位误差纠正前Vrt、Lng、Lat方向CTV-PTV外放边界(MPTV)分别为10.981、10.514、7.381mm,摆位误差纠正后MPTV分别为0.925、1.353、0.440mm。摆位误差纠正前和纠正后肿瘤中心点移动距离分别为(8.890±7.222)mm和(1.021±1.075)mm,CBCT纠正后摆位误差范围较纠正前显著减少(P<0.05)。结论宫颈癌IMRT中每日行CBCT校正可明显减少摆位误差,提高放疗精确性。

Objective To explore the application value of daily cone beam computed tomography(CBCT) imaging in correcting setup errors for cervical cancer radiotherapy. Methods A total of eighteen cases of cervical cancer treated with intensity modulated radiotherapy(IMRT) received daily CBCT imaging during the treatment fraction to position the patient’s bony anatomy according to planning CT scans. The setup error of Vertical(Vrt), Longitudinal(Lng), Lateral(Lat) were received using pre-and post-fraction CBCT scans. The position error were recorded and analyzed. Results A total of 906 CBCT scans were analyzed for 18 cervical cancer patients using pre-and post-fraction CBCT scans. The overall mean(M), systematic error(∑), and random error(σ) of Vrt direction before and after correction were 0.581,4.068,1.160 mm and 0.049,0.292,0.277 mm respectively. M,∑,σ of Lng direction before and after correction were 0.789, 3.637,2.031 mm and 0.477,0.391,0.539 mm, and Lat direction before and after correction were-0.375, 2.515,1.564 mm and 0.094, 0.109, 0.238 mm. The PTV margins required for the CTV were 10.981 mm, 10.514 mm, 7.381 mm. After correction, the coverage margins were 0.925 mm, 1.353 mm, 0.440 mm. The moving distance of center point in tumor was(8.890±7.222) mm before CBCT, and after correction the distance was(1.021±1.075) mm. There were significant reduced setup errors after correction(P<0.05). Conclusion The daily CBCT correction in IMRT of cervical cancer can significantly reduce setup errors and improve the accuracy of radiotherapy.