锥形束CT对鼻咽癌两种体位固定方式摆位误差的验证分析

目的测量并比较分析鼻咽癌两种固定方式的摆位误差，并确定其计划靶区（planning target volume,PTV）外放边界。方法73例鼻咽癌患者采用头枕+头颈肩热塑面罩固定35例和发泡胶+头颈肩热塑面罩固定38例均实施调强放射治疗，在治疗摆位纠正前进行锥形束(cone beam computed tomography, CBCT)扫描共429次，其中头枕+头颈肩热塑面罩固定组201次，发泡胶 +头颈肩热塑面罩固定组228次。将获得的CBCT图像和计划CT图像匹配，得到X、Y、Z轴方向上的平移及旋转误差，并对摆位误差进行分析。结果头枕+头颈肩热塑面罩固定组在X、Y、Z轴上的平移误差分别为(0.11±0.08)、(0.15±0.12)、（0.12±0.10）cm,旋转角度误差分别为 0.59°±0.53°、0.84°±0.62°、0.61°±0.51°，外放边界分别为0.33、0.46、0.37 cm;发泡胶+头颈肩热塑面罩固定组的平移误差分别为（0.09±0.07）、（0.13±0.09）、（0.11±0.10）cm, 旋转角度误差分别为0.55°±0.49°、0.69°±0.51°、0.58°±0.46°，外放边界分别为0.28、0.39、0.35 cm。采用发泡胶+头颈肩热塑面罩固定组和头枕+头颈肩热塑面罩固定组在Y轴上的平移及旋转角度误差数据差异均具有统计学意义（P＜0.05)。结论采用发泡胶+头颈肩热塑面罩固定鼻咽癌患者，可减小其在Y轴（头脚）方向的平移及旋转误差。CBCT可精确地测量出摆位误差，对外放边界的确定有指导意义。

Analysis of setup errors detected in cone beam computed tomography using two different immobilization techniques for nasopharyngeal carcinoma

Abstract:ObjectiveTo measure and evaluate the setup errors in patients with nasopharyngeal carcinoma (NPC) immobilized with two different techniques, and determine the proper margins extended from clinical target volume (CTV) to planning target volume (PTV).Methods73 NPC patients treated with intensity modulated radiotherapy (IMRT) were divided into two groups. All the patients received cone beam computed tomography (CBCT) scan (429 times) and CT image matching before every treatment and correction. 35 patients were immobilized using standard plastics pillow with head and neck thermoplastics masks (standard plastics pillow group) and received 201 CBCT scans, 38 patients were immobilized using polyurethane foam sealing agent pillow with head and neck thermoplastics masks (polyurethane foam sealing agent group) received 228 CBCT scans. The shift and rotation setup errors in right left (X), superior inferior (Y) and anterior posterior (Z) directions were recorded and analyzed.ResultsIn the standard plastics pillow group, the shift errors in X,Y and Z axes were (0.11±0.08)cm, (0.15±0.12)cm and (0.12±0.10) cm respectively, the corresponding rotation errors were 0.59°±0.53°, 0.84°±0.62°and 0.61°±0.51°, and the margins from CTV to PTV were 0.33 cm, 0.46 cm and 0.37 cm. In the polyurethane foam sealing agent pillow group, the shift errors in X,Y and Z axes were (0.09±0.08)cm, (0.13±0.09)cm and (0.11±0.10)cm respectively, the corresponding rotation errors were 0.55°±0.49°, 0.69°±0.51°and 0.58°±0.47°, and the margins from CTV to PTV were 0.28 cm, 0.39 cm and 0.35 cm. The differences of shift and rotation errors in Y axis between the two groups were statistically significant (both P<0.05).ConclusionsThe shift and rotation errors in Y axis can be obviously decreased by immobilization with polyurethane foam sealing agent pillow plus head and neck thermoplastics masks during IMRT of NPC patients. CBCT can be used in the precise measure of setup errors, which is instructive to determine the margins from CTV to PTV.