在线千伏级锥形束CT引导前列腺癌调强放疗摆位误差研究

目的 通过千伏级锥形束CT(KV-CBCT)在线测量前列腺癌调强放疗的摆位误差及图像引导后的残余误差,确定前列腺癌患者外照射治疗计划中CTV外放PTV的边界大小.方法 入选7例接受根治性调强放疗的前列腺癌患者,每例患者每周至少行KV-CBCT在线校正治疗体位2次.采用常规皮肤标记激光对位后采集图像,将所获得CBCT与计划CT图像进行灰度自动配准.计算摆位误差并进行在线评价,若摆位误差＞2 mm则调整治疗床进行纠正.纠正后重新采集CBCT图像进行配准,计算残余误差.根据摆位误差和残余误差分别计算纠正前后临床靶体积(CTV)至计划靶体积(PTV)外放边界大小.结果 共获取197幅KV-CBCT图像.7例患者左右、头脚、前后方向系统误差和随机误差分别为3.1和2.1、1.5和1.8、4.2和3.7 mm,外放边界分别为9.3、5.1、13.0 mm.经KV-CBCT引导纠正后左右、头脚、前后方向系统残余误差和随机残余误差分别为1.1和0.9、0.7和1.1、1.1和1.3 mm,外放边界分别为3.4、2.5、3.7 mm.结论 在线KV-CBCT引导放疗技术可减小前列腺癌患者摆位误差、提高摆位精度,CTV外放PTV边界可缩小至3～4 mm.

Positioning errors assessed with kV cone-beam CT for image-guided prostate radiotherapy

Objective To assess set-up errors measured with kilovoltage cone-beam CT (KV-CBCT), and the impact of online corrections on margins required to account for set-up variability during IMRT for patients with prostate cancer. Methods Seven patients with prostate cancer undergoing IMRT were enrolled onto the study. The KV-CBCT scans were acquired at least twice weekly. After initial set-up using the skin marks, a CBCT scan was acquired and registered with the planning CT to determine the setup errors using an auto grey-scale registration software. Corrections would be made by moving the table if the setup errors were considered clinically significant ( i. e. , ＞ 2 mm). A second CBCT scan was acquired immediately after the corrections to evaluate the residual error. PTV margins were derived to account for the measured set-up errors and residual errors determined for this group of patients. Results 197 KV-CBCT images in total were acquired. The random and systematic positioning errors and calculated PTV margins without correction in mm were:a) Lateral 3. 1,2. 1,9. 3;b) Longitudinal 1.5, 1.8, 5. 1 ;c) Vertical 4. 2,3.7, 13.0. The random and systematic positioning errors and calculated PTV margin with correction in mm were:a) Lateral 1.1,0. 9, 3.4;b) Longitudinal 0. 7, 1.1, 2. 5;c) Vertical 1.1, 1.3, 3.7. Conclusions With the guidance of online KV-CBCT, set-up errors could be reduced significantly for patients with prostate cancer receiving IMRT. The margin required after online CBCT correction for the patients enrolled in the study would be appoximatively 3-4 mm.