鼻咽癌适形放疗实施过程精确度和重复性研究

A Study of Accuracy and Reproducibility in Conformal Radiotherapy for Nasopharyngeal Carcinoma

[目的]研究鼻咽癌放射治疗的实施过程中照射野的摆位精度和重复性的可能误差,为临床放疗的照射野边界的计划靶区(PTV)的设计提供依据。[方法]通过对35例病人首次放疗前的射野验证照片和1例病人全程放疗的每次射野验证照片(共36次)与计划设计时的模似定位照片进行比较分析,计算其误差值。[结果]不同病人的摆位误差和单个病人摆位的重复性误差平均值分别为(0.88±1.44)mm和(0.61±1.11)mm,两组实验中摆位偏差>3mm的检测次数分别占6.6%和3.5%。[结论]设计鼻咽癌放疗计划PTV应至少包括2～3mm的摆位误差,放疗前拍验证照片可及时发现和纠正较大的摆位误差,建议作为常规质控程序执行。

To study the positioning error between treatment planning and patient setup during conformal radiotherapy for patients with nasopharyngeal carcinoma(NPC),so as to provide a protocol for clinical treatment planning.Thirty-five cases with NPC treated by conformal radiotherapy techniques were studied.The simulation films and the verification films were taken for each patient prior to the treatment.One of these cases was selected to take verification films for every fraction over the full treatment course.The verification film was then overlapped on the associated simulation film by aligning anatomical landmarks.The absolute distance discrepancy of associated reference points shifted between simulation film and verification film was used to access the magnitude of the positioning error.The average positioning error of two lateral irregular fields for35cases with NPC was(0.88±1.44)mm,and(0.61±1.11)mm for the single case.No significantly difference was found for the positioning error among different fields,various reference points and different treatment phases(P>0.05).A margin of3mm was sufficient to compensate for the positioning error between the treaement planning and the treatment delivery.[Conclusion]Better immobilization and repeated verification help to improve the accuracy of patient setup.A variety of verification such as simulation verification and treatment verification should be widely used as a QA standard,so as to correct the positioning error of patient setup.