胸部肿瘤放疗中呼吸运动对偏中心处点剂量和面剂量的影响

Impact of Respiratory Motion on Point and Planar Radiation Dose for Thoracic Tumor at Off-Center Location

目的:评估呼吸运动的幅度、频率对放疗计划中偏中心处物理剂量产生影响的程度。方法:入组肺癌患者12例,四维CT定位,最大密度投影确定内大体肿瘤(internal gross target volume,IGTV),外扩临床靶区(clinical target volume,CTV)、计划靶区(planning target volume,PTV),而后设计调强放疗放疗物理计划。将计划移植到四维程控运动模体QUASAR上生成模体计划,而后在QUASAR上以振幅为0、3、6、8、10、15、20 mm和频率为15、20F/min做“模拟呼吸运动”的条件下,对模体计划偏中心处的点剂量和面剂量进行测量,比较分析测量的点剂量和面剂量与计划输出的差异。结果:偏中心处点剂量的偏差与幅度有成正比的趋势,频率对点剂量的影响很小;当振幅>8 mm,平面剂量的γ通过率(3mm,3%,10%的标准)<60%,剂量偏差大。结论:当振幅≥8 mm时,振幅对偏中心处剂量的影响很大,受呼吸运动影响面剂量γ通过率降低了30%。

Objective:To evaluate the impact of the amplitude and frequency of respiratory movement on the physical ra-diation dose at off-center location.Methods:A total of 12 patients with lung cancer were enrolled.Internal gross target vol-ume,clinical target volume and planning target volume were determined by four-dimensional computed tomography and maxi-mum density projection;and then IMRT plan was designed for every patient.We transplanted plans into a four dimensional QUASAR phantom,and generated a phantom plan.Point and planar radiation dose at off-center location were measured by the QUASAR phantom when patients breathed with amplitude of 0,3,6,8,10,15 or 20 mm and frequency of 15 or 20 f/min.Acquired data were compared with planned output.Results:At the off-center location,the deviation of point dose was proportional to the amplitude,and the frequency had little effect on point dose.When the amplitude was greater than 8 mm,theγpass rate of planar dose(3 mm,3%,10%standard)was less than 60%,which was a large dose deviation.Con-clusion:When the amplitude is greater than 8 mm,the ampli-tude has a great influence on the dose at the off-center loca-tion,theγpass rate of planar dose affected by respiratory movement has decreased by 30% .