用数字模体模拟利用4DCT计算累积剂量偏差  

Simulation of the discrepancy in 4DCT-based cumulative dose using digital phantoms

作　　者：柳刚[1] 杨志勇[1] 梁志文[1] 杨晶[1] 聂鑫[1] 曹婷[1] 全红[2] 张俊[3] 李勤[1] Liu Gang Yang Zhiyong Liang Zhiwen Yang Jing Nie Xin Cao Ting Quan Hong Zhang Jun Li Qin(Center of Radiotherapy Oncology, Union Hospital, Tongji Medical Colloge, Huazhong University of Science and Technology, Wuhan 430023, Chin School of Physics and Technology, Wuhan University, Wuhan 430072, China Department of Radiation Oncology , Zhongnan Hospital, Wuhan University, Wuhan 430071, China)

机构地区：[1]华中科技大学同济医学院附属协和医院肿瘤中心,武汉430023 [2]武汉大学物理科学与技术学院,430072 [3]武汉大学中南医院放疗科,430071

出　　处：《中华放射肿瘤学杂志》2017年第7期790-794,共5页Chinese Journal of Radiation Oncology

摘　　要：目的 用计算机仿真模拟评估由于患者呼吸不均匀导致的用4DCT图像与用扫描4DCT时的实时呼吸图像计算的累积剂量之间的差异.方法 用某个患者的4DCT图像生成数字模体,通过计算机模拟各种形式的不均匀呼吸曲线形成4DCT图像及扫描4DCT时的实时呼吸图像.在参考图像上制作一个6个野均分的IMRT计划,用4DCT和扫描4DCT时的实时呼吸图像分别计算累积剂量且记为D4D和Dall,并计算二者之间的差异,评价呼吸运动模式变化对该差异的影响.结果两种累积剂量之间的差异依赖于平均运动幅度和幅度标准差的变化.当平均运动幅度从5 mm增加到15 mm时,靶区ΔDmin（ΔD99）从2.39%（2.04%）增加到11.91%（5.24%）,而当幅度的标准差从平均幅度的15%增加到平均幅度的45%时,靶区ΔDmin（ΔD99）从5.93%（2.15%）增加到14.65%（5.01%）;当平均周期从3 s增加到5 s或者周期标准差从平均周期的10%增加到40%时,靶区ΔDmin（ΔD99）均〉6.0%（2.0%）而〈9.0%3.0%）;当肿瘤直径为2 cm、3 cm以及4 cm时,靶区ΔDmin（ΔD99）分别为11.88%（5.50%）、6.91%（2.42%）以及7.53%（3.62%）.结论 当呼吸运动不均匀时,用4DCT计算的累积剂量和用扫描4DCT时的实时呼吸图像计算的累积剂量之间存在较大差异,且该差异依赖于呼吸运动的平均幅度和幅度的标准差,而平均周期及周期标准差的变化对其影响不大,该差异随肿瘤体积变化的趋势不明显.Objective To conduct a computer simulation to evaluate the discrepancy between the cumulative doses calculated by four-dimensional computed tomography （4DCT） images and 4DCT scans （for real-time respiratory motions） due to the patient＆#39;s irregular breathing.Methods A series of digital phantoms were generated from a patient＆#39;s 4DCT images to simulate 4DCT images and 4DCT scans （for real-time respiratory motions） resulting from various irregular breathing curves.A six-field intensity-modulated radiotherapy plan was generated.Two cumulative doses in the target were calculated.The first one, named Dall, was calculated by tracking the point displacements in the target manifested on the 4DCT images;the second one, named D4D, was calculated based on the point displacements along the whole breathing motion during 4DCT scanning.Dose discrepancy between D4D and Dall was calculated to evaluate the correlation between breathing pattern and dose discrepancy in the target.Results The dose discrepancy in the target was correlated with mean motion excursion and the standard deviation of motion excursion.ΔDmin（ΔD99） in the target increased from 2.39%（2.04%） to 11.91%（5.24%） as the mean motion excursion increased from 5 mm to 15 mm, and increased from 5.93%（2.15%） to 14.65%（5.01%） as the standard deviation of motion excursion increased from 15% to 45% of the mean motion excursion.When the mean period increased from 3 s to 5 s or the standard deviation of period increased from 10% to 40% of the mean period,ΔDmin（ΔD99） in the target was greater than 6.0%（2.0%）, but less than 9.0%（3.0%）.When the target diameter was 2 cm, 3 cm, and 4 cm,ΔDminΔD99） in the target was 11.88%（5.50%）, 6.91%（2.42%）, and 7.53%（3.62%）, respectively.Conclusions There is a large discrepancy between the cumulative doses calculated using 4DCT images and 4DCT scans （for real-time respiratory motions） when the patient has irregular breathing.This dose discrepancy depends on mean motion ex

关 键 词：体层摄影术 X线计算机 呼吸运动 累积剂量 

分 类 号：R730.44[医药卫生—肿瘤]