摘要目的 评估千伏级射野验证片与千伏级锥形束CT对鼻咽癌调强放射治疗摆位误差监测的应用价值.方法 获取本中心接受调强放射治疗的10例鼻咽癌共计81次治疗前的千伏级射野验证片和千伏级锥形束CT图像,分别将二者与数字重建照片、计划CT图像进行匹配,获取两种影像方法所监测的治疗等中心点在左右、头尾、前后方向的摆位误差,分别计算两者所监测的三维方向的平均绝对误差值、平均摆位误差和标准差;计算两者所监测摆位误差的差值,评估两者对摆位误差监测的差异性.结果 千伏级射野验证片和千伏级锥形束CT所监测的左右、头尾、前后方向的平均绝对误差值分别为0.7 mm、1.6mm、0.9 mm和0.9 mm、1.7 mm、0.9 mm;两者所监测的左右、头尾、前后方向的平均摆位误差和标准差分别为(0.4±1.1)mm、(1.2±1.6)mm、(-0.3±1.0)mm和(-0.1±0.9)mm、(-1.4±1.5)mm、(0.2±1.1)mm,且在三个方向均有统计学意义(P=0.00).两者所监测的摆位误差的平均差异在三维方向分别为0.8mm、2.7mm和0.7mm.结论 鼻咽癌调强放射治疗各方向的平均摆位误差不超过2 mm.KV级射野验证片和KV级锥形束CT对鼻咽癌摆位误差监测的差异在头尾方向最明显,考虑到锥形束CT提供详细的解剖学信息及空间三维影像,故推荐其为监测鼻咽癌摆位误差的首选方法.

abstractsObjective To evaluate the application value of two-dimensional kilovoltage (2D kV) imaging and kilovoltage cone beam CT (KV CBCT) in set-up verification for patients with nasopharyngeal carcinoma receiving intensity-modulated radiation therapy.Methods 10 patients with nasopharyngeal carcinoma were enrolled into the study.Each patient was imaged with a pair of orthogonal 2D kV images in treatment position before the CBCT procedure at least once a week.A total of 81 pairs of 2D KV images and KV CBCT were acquired.The 2D kV images and kV CBCT scans were registered to the digitally reconstructed radiographs and planning CT scans,respectively.The error (including absolute error,average error,and standard error) values were calculated for the 2DkV images and kV-CBCT in left-right (LR),superior-inferior (SI),and anterior-posterior (AP) directions.Differences between CBCT and EPID were calculated and evaluated in three dimensions.Results The average absolute errors of2D kV images and KV CBCT were 0.7 mm and 0.9 mm,1.6 mm and 1.7 mm,and 0.9 mm and 0.9 mm in LR,SI and,AP directions,respectively.The mean±standard error measured by 2D KV and KV CBCT in LR/SI/AP directions were (0.4±1.1) mm,(1.2±1.6) mm,(-0.3±1.0) mm and (-0.1±0.9) mm,(-1.4±1.5) mm,(0.2±1.1) mm.The setup error measured by 2D KV were significantly different from that by kV-CBCT for the three directions (P =0.00).The differences between 2DKV images and KV-CBCT in LR,SI,and AP directions were 0.8 mm,2.7 mm,and 0.7 mm,respectively.Conclusions The average errors for NPC IMRT are no more than 2 mm.The 2DkV images and kV CBCT scans show non-negligible measurement differences in SI direction when measuring the same patients near-simultaneously.Considering KV CBCT offers adequate volumetric image quality for nasopharyngeal carcinoma in radiotherapy and should be used for image guidance firstly.