胸部定位参考线配合红外定位系统在鼻咽癌放疗中的应用

摘要

Objective To verify whether the chest positioning reference line combined with an infrared positioning system (OPS) helps to reduce the linear and rotational errors in intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC).Methods Sixty NPC patients were randomized into two groups to receive IMRT with two positioning strategies using chest positioning reference line combined with OPS (30 cases) or conventional positioning (30 eases).All the patients were immobilized with thermoplastic head-and-shoulder mask.Before the scanning,the patients with chest positioning reference line combined with OPS were asked to lie on the positioning bed in a supine position adjusted according to the position of the thermoplastic mask and the head-and-shoulder fixation plate;the chest reference line was determined and then traced with OPS positioning balls.In patients with conventional positioning,the position of the patients was adjusted according to the reference lined defined by the position of the body relative to the fixation plate.Intensity-modulated treatment plans were carried out using the treatment planning system (TPS) after contrast CT scans.The linear and rotational errors of the two positioning methods were analyzed using kilovoltage cone-beam CT scans.Results The linear and rotational errors of positioning in the right-left (X),superior-inferior (Y),and anterior-posterior (Z) directions were calculated in the two groups using the bone registration and gray plus rotation registration algorithms.The linear errors in X,Y,and Z directions were (-0.21± 1.13),(0.14± 0.90),and (-0.31±1.12) mm in chest reference line group,and were (-0.59±1.76),(0.76±1.60),and (-0.41±2.13)mm in conventional positioning group,respectively,and the errors showed significant differences between the two groups (P=0.664 000,0.000 038,and 0.421 000,respectively).The rotational errors in X,Y,and Z directions also differed significantly between the two groups (0.23°±0.61° vs 0.85°±1.31°,P=0.000 150;0.35°±0.42° vs 0.47°±0.61°,P=0.054 200;and 0.11°± 0.72° vs 0.91°±1.32°,P=0.000 430,respectively).Conclusion The application of chest positioning reference line with OPS can effectively reduce random errors in positioning of the patients for IMRT to ensure the accuracy and repeatability of positioning and improve the precision of radiotherapy.%目的:应用千伏级锥形束CT(CBCT)验证胸部定位参考线配合红外定位系统(OPS)减小鼻咽癌调强放疗摆位线性误差与旋转误差.方法:随机选取不同定位方式的鼻咽癌患者共60例分成两组,其中采用胸部定位参考线配合OPS的患者30例,常规定位的患者30例,60例患者均采用头颈肩热塑体膜固定体位.胸部定位参考线配合OPS的患者扫描前根据患者与头颈肩热塑体膜相对位置及头颈肩固定体板的位置仰卧于定位床上,确定胸部参考线并在其标记线上贴上相应OPS定位小球,其余治疗摆位时患者体位与体板相对位置以定位参考线为准,然后进行增强扫描定位,将定位图像传输至治疗计划系统(TPS)进行调强治疗计划.应用CBCT扫描对两种定位方法进行误差分析.结果:两组图像应用骨性和灰度加旋转配准算法计算与定位图像配准,得到X(左右方向)、Y(头脚方向)、Z(前后方向)线性和旋转误差.设置胸部参考线与未设置胸部参考线两组患者X、Y、Z方向摆位线性误差分别为(-0.21±1.13)、(0.14±0.90)、(-0.31±1.12)mm和(-0.59±1.76)、(0.76±1.60)、(-0.41 ±2.13)mm,P值分别为0.664000、0.000 038、0.421000;X、Y、Z方向摆位旋转误差分别为0.23°±0.61°、0.35°±0.42°、0.11°±0.72°和0.85°±1.31°、0.47°±0.61°、0.91°±1.32°,P值分别为0.000 150、0.054 200、0.000 430.结论:通过胸部定位参考线配合OPS,能有效减少来自摆位的随机误差,同时保证治疗体位的精确性和重复性,提高放疗精度.