颈胸部肿瘤应用头颈肩体热塑膜放疗的摆位误差

Setup errors in radiotherapy on neck-thoracic tumor fixed by head-neck-shouder-body theroplastic mask

目的利用射野影像系统(EPID)测量颈胸部肿瘤应用头颈肩体热塑膜放疗的摆位误差,并计算出计划靶区(PTV)的外扩范围。方法放射治疗的颈胸部恶性肿瘤患者20例,制作头颈肩体热塑膜,通过比较计划射野参考图像(DRR)和实际射野验证图像(EPI)相关骨性标记的位置偏移,计算出三维方向的摆位误差,并由公式MPTV=2.5Σ+0.7σ分别计算出不考虑与考虑靶区内扩边的具体MPTV值。结果 20例患者在三维方向上的摆位系统误差标准差分别为0.95mm、0.26mm和0.57mm,随机误差标准差分别为1.46mm、0.53mm和0.99mm。不考虑靶区内扩边的MPTV值分别为3.4mm、1.0mm和2.1mm,考虑的为7.38mm、6.62mm和6.88mm。结论颈胸部肿瘤患者应用头颈肩体热塑膜固定,体位重复性和准确性均相对较高;实测本院放疗中心的MPTV值,使制定的精确放疗计划更具科学性。

Objective To establish a method using electronic portal imaging device（EPID） to acquire the setup errors and to calculate the margin of planning target volume（MPTV） for neck-thoracic tumor in radiotherapy.Methods Twenty patients with neck-thoracic tumors were fixed by head-neck-shouder-body theroplastic mask.Setup errors in X（medio-lateral）,Y（antero-posterior） and Z（cranio-caudal） direction were calculated by comparing the position offset of the relevant osseous marks between DRR and EPI.According to the formulation,the size of MPTV with or without consideration of organ motion was calculated as well.Results The standard deviations of systematic errors（Σ）were 0.95 mm,0.26 mm and 0.57 mm at X,Y and Z direction,respectively.The standard deviations of random errors（σ） were 1.46 mm,0.53 mm and 0.99 mm at X,Y and Z direction,respectively.Without consideration of organ motion,the sizes of MPTV were 3.4 mm,1.0 mm and 2.1 mm at X,Y and Z direction,respectively.With consideration of organ motion,the sizes of MPTV were 7.38 mm,6.62 mm and 6.88 mm at X,Y and Z direction,respectively.Conclusion Fix ation with head-neck-shouder-body theroplastic mask could provide a relatively higher assurance in position repeatability and accuracy for neck-thoracic tumor patients.Actually measuring the value of MPTV is more scientific in planning the radiotherapy regime.