不同运动幅度下笔形束质子与调强光子治疗的肿瘤剂量鲁棒性对比研究

Comparative study of tumor dose robustness in pencil beam proton therapy vsintensity-modulated photon therapy under varying motion amplitudes

目的通过量化不同运动幅度下笔形束质子(PBSPT)计划和调强光子(IMRT)计划的剂量差异,分析PBSPT计划和IMRT计划在不同图像中对靶区运动的鲁棒性。方法搭建幅度为4和_(8mm)的胸部仿真模体运动平台,扫描平均密度投影(AIP)、最大密度投影(MIP)和平扫CT模拟定位影像。使用Eclipse计划系统在6组运动模体CT影像上生成PBSPT计划和IMRT计划,2种计划的单次照射剂量均为200 cGy。将AIP PBSPT计划分别配准到吸气末(T0)和呼气末(T50)相位影像上,计算其剂量分布。同时,将3组图像中的PBSPT计划进行鲁棒性分析。使用胶片采集实际照射剂量学参数,通过配对t检验或秩和检验评估放疗计划的鲁棒性。结果运动幅度增大,T0和T50中的AIP光子ΔV_((100))中位值分别为-7.15%和-7.50%,质子ΔV_((100))中位值分别为-18.45%和-16.10%。AIP光子Δ(V_(R)-V_(TR))中位值分别为-37.09和-38.03 cm^(3),质子Δ(V_(R)-V_(TR))中位值分别为-3.80和-2.27 cm^(3)。质子无剂量扰动下V_((100))差异无统计学意义,t=1.538,P=0.185;最大剂量扰动下靶区V_((100))差异有统计学意义,t=2.925,P=0.033。光子戴斯相似性系数(DSC)_(8mm)均大于DSC_(4mm),在所有图像中差异有统计学意义,t值分别为-2.666、-3.674和-24.648,P值分别为0.045、0.014和<0.001。AIP图像和平扫CT图像的质子包容性系数(SI)_(8mm)较SI_(4mm)出现明显下降,差异有统计学意义,Z值分别为-2.908和-2.945,P值分别为0.004和0.003。质子均匀性指数(HI)_(4mm)和HI_(8mm)差异有统计学意义,t值分别为-4.134、-2.913和-16.997,P值分别为0.009、0.004和<0.001。结论PBSPT计划对靶区运动较IMRT计划更为敏感。MIP图像中的计划能保证靶区受到足量处方剂量照射,但会在周围产生较大高量区域,不能更好地保护危及器官。在运动幅度较大的情况下,平扫CT图像不能正确反映靶区位置和大小,易对剂量分布产生影响。

Objective To quantify the dose difference between pencil beam scanning proton therapy(PBSPT)and intensitymodulated radiation therapy(IMRT)under multiple motion amplitudes,and to analyze the robustness of PBPT and IMRT to target motion in different images.Methods Motion platforms with 4mm and 8mm amplitudes were built,and average intensity projection(AIP),maximum intensity projection(MIP),and plain scan CT simulation localization images were scanned.PBSPT and IMRT plans of six sets of motion target CT images using the Eclipse planning system were generated,and the single irradiation dose of these two plans was 200cGy.The AIP PBSPT plans were registered to the end-inspiration(T0)and end-expiration(T50)phase images,and their dose distributions were calculated.The three PBSPT plans were analyzed for robustness.The delivery dosimetric parameters were captured on EBT3film,to evaluate the planning robustness though the paired t test and the rank sum test.Results As the amplitude of motion increased,the IMRTΔV_((100))median values in T0and T50were-7.15%and-7.50%,the PBSPTΔV_((100))median values were-18.45%and-16.10%.The IMRTΔ(V_(R)-V_(TR))median values in T0and T50 were-37.09and-38.03cm^(3),the PBSPTΔ(V_(R)V_(TR))median values were-3.80and-2.27cm^(3).There was no statistically significant difference in proton dose without perturbation(t=1.538,P=0.185);there was a statistically significant difference in the target area under the maximum dose perturbation,(t=2.925,P=0.033).The Dice similarity coefficient(DSC)_(8mm) were higher than DSC4mmin all images,and the difference were statistically significant,with t values of-2.666,-3.674,and-24.648,and Pvalues of 0.045,0.014,and<0.001,respectively.The PBSPT sensitivity index(SI)_(8mm) were lower than those of SI4mmin AIP and plain CT images,the difference were statistically significant,with Zvalues of-2.908and-2.945,and Pvalues of 0.004and 0.003,respectively.The difference between homogeneous index(HI)_(4mm)and HI8mmof PBSPT were statistically significant,with t values of-4.134,-2.913,and-16.997,and Pvalues of 0.009,0.004,and<0.001,respectively.Conclusions PBSPT demonstrates a higher sensitivity to target motion than IMRT.The plans in MIP images can ensure that the target area receives an adequate prescribed dose,but they may produce a larger high-dose area around,failing to better protect organs at risk.In cases of larger motion amplitudes,plain CT images cannot accurately reflect the target position,which may affect the dose distribution easily.