铅点标记体模辅助配准方法在乳腺癌CBCT中的误差研究

Investigation of scanning position and image registration methods during cone-beam computer tomography in breast cancer using lead points

目的探讨铅点标记的体模在减少乳腺癌图像引导放疗（image guide radiation therapy,IGRT）中的误差,以及应用锥体束CT（cone beam computer tomography,CBCT）扫描时的最佳配准方法。方法选择本院就诊的女性乳腺癌术后接受放射治疗的患者30例,于定位座标原点0度与＋90度/-90度位置的体模上预置铅点标记,CBCT扫描后获取的图像与计算机断层显像模拟技术（computer tomography simulation）重建所生成的CT图像比较验证,将铅点＋灰度配准、铅点配准和灰度配准分别与手工配准比较,求取所摄图像在X、Y、Z轴和水平转角实际产生摆位误差差值以及相应手段的配准时间。结果30例患者使用体模铅点标记法提高了配准准确性。铅点＋灰度与手动在u旋转方向上不同,分别为1.74度和1.67度（t=1.12,P=0.002）;铅点配准与手动配准在x轴平移及y轴平移方向上均不同,分别为0.34 mm和2.75 mm（t=5.76,P=0.01）及1.03 mm和0.95 mm（t=0.13,P=0.032）;灰度配准与手动配准在x轴和u旋转方向上不同,分别为4.20 mm和2.75 mm（t=2.98,P=0.003）及1.25度和1.67度（t=-1.00,P=0.03）。铅点配准＋灰度配准符合率最高（87.23%）,铅点配准为（75.2%）,灰度配准为（73.95%）。手动配准时间（2-4.5 min）〉铅点＋灰度配准（0.75-1.3 min）〉灰度配准（0.5-0.75 min）〉铅点配准（0.25-0.5 min）。结论使用体模铅点标记法对改进乳腺癌摆位误差的图像验证具有实际意义,结合配准时间和配准准确性,铅点配准＋灰度配准方法最佳。

Objective To explore set up error and image registration methods during conebeam computer tomography（ CBCT） in breast cancer using lead point mark phantom. Methods Sixty CBCT images acquired before radiation and the corresponding planning computed tomography（ CT） images of breast cancer were selected for further investigation. Preset lead points at the origin of the coordinates on the phantom 0° and ＋ 90° /- 90° position. The results of registration as well as time cost were compared among different registration methods of lead point match,gray value match,manual match,and lead point plus gray value match. Results Patients with the use of lead point mark phantom improved registration accuracy. Compared with manual match,set-up errors of u rotation in lead point plus gray value match（ 1. 74° vs1. 67°,t = 1. 12,P = 0. 002）,of LR-axis and SI-axis in lead point match（ 0. 34 mm vs 2. 75 mm,t = 5. 76,P = 0. 01; 1. 03 mm vs 0. 95 mm,t = 0. 13,P = 0. 032）,and of LR-axis and u rotation in the gray value match（ 4. 20 mm vs 2. 75 mm,t = 2. 98,P = 0. 003; 1. 25°vs 1. 67°,t =- 1. 00,P = 0. 03） were significantly different. Compared with manual match,the coincidence rate of lead point plus gray value match was the hightest（ 87. 23%）,followed by lead point match and the gray value match（ 75. 2% and 73. 95%）. The time cost of each registration method from longest to shortest was 1. 00 - 4. 50 minutes for manual match,0. 75 - 1. 30 minutes for lead point plus gray value,0. 50 - 0. 75 minutes for gray value match,and 0. 25 -0. 50 minutes for lead point match. Conclusion Phantom with lead points is useful for image registration of CBCT and planning CT in patients with breast cancer.