Greer P B, Mortensen T M, Jose C C
Oncology Centre, Auckland Hospital, New Zealand.
Int J Radiat Oncol Biol Phys. 1998 Jul 15;41(5):1193-9. doi: 10.1016/s0360-3016(98)00160-6.
The two setup methods commonly used to determine the anterior-posterior isocenter location in pelvic radiotherapy are to align lateral localization lasers with lateral skin tattoos on the patient, or to set the couch height so that the isocenter is at a fixed height (determined during simulation or treatment planning) above the couch top. This study was implemented to determine which technique gives more accurate patient treatment by comparison of the anterior-posterior setup variation measured with electronic portal imaging.
Eleven supine prostate patients were treated with tattoo localization and 159 left-lateral portal images were taken during the treatments. The field displacements were then determined by template matching. These patients were compared to nine patients (205 images) set up to a fixed isocenter height. Similarly, eight prone rectal patients (136 right-lateral images) set up to tattoos were compared to six patients (108 images) set up to a fixed height. The patients were not immobilized and were all treated with three field techniques on a hard couch top. The overall mean treatment position deviation and the standard deviation of the displacements (total setup variation) were calculated for each patient group along with the systematic (simulator-to-treatment) and the random (treatment-to-treatment) setup variation.
The mean treatment position deviations were 3.3 mm anterior and 5.2 mm posterior with the tattoo method for the prostate and rectal patients, respectively. These mean position deviations were 0.4/0.1 mm anterior with the fixed height technique. The total setup variations were 4.6/5.2 mm (1 SD) with tattoo localization and 1.7/1.5 mm (1 SD) with the fixed height method. Similarly, random variation was 2.3/3.3 mm (1 SD) with the tattoo method compared to 1.3/1.2 mm (1 SD) with the fixed height method. Systematic variation was 3.7/4.5 mm (1 SD) compared to 1.2/1.1 mm (1 SD).
The fixed height technique gives much more accurate localization of the anterior-posterior isocenter in pelvic radiotherapy than lateral skin tattoos.
盆腔放射治疗中常用于确定前后等中心位置的两种设置方法是，将侧向定位激光与患者身上的侧向皮肤纹身对齐，或者设置治疗床高度，使等中心位于治疗床顶部上方的固定高度（在模拟或治疗计划期间确定）。本研究旨在通过比较电子门静脉成像测量的前后设置变化，确定哪种技术能为患者提供更精确的治疗。
11例仰卧位前列腺患者采用纹身定位进行治疗，治疗期间采集了159张左侧门静脉图像。然后通过模板匹配确定野位移。将这些患者与9例设置为固定等中心高度的患者（205张图像）进行比较。同样，将8例俯卧位直肠癌患者（136张右侧图像）采用纹身定位与6例设置为固定高度的患者（108张图像）进行比较。患者未进行固定，均在硬治疗床上采用三野技术进行治疗。计算每个患者组的总体平均治疗位置偏差和位移标准差（总设置变化），以及系统（模拟到治疗）和随机（治疗到治疗）设置变化。
前列腺和直肠癌患者采用纹身法时，平均治疗位置偏差分别为向前3.3 mm和向后5.2 mm。采用固定高度技术时，这些平均位置偏差分别为向前0.4/0.1 mm。纹身定位时总设置变化为4.6/5.2 mm（1标准差），固定高度法为1.7/1.5 mm（1标准差）。同样，纹身法的随机变化为2.3/3.3 mm（1标准差），而固定高度法为1.3/1.2 mm（1标准差）。系统变化分别为3.7/4.5 mm（1标准差）和1.2/1.1 mm（标准差）。
在盆腔放射治疗中，固定高度技术在前后等中心定位方面比侧向皮肤纹身精确得多。
