Comparative study of tumor dose robustness in pencil beam proton therapy vs intensity-modulated photon therapy under varying motion amplitudes
Objective To quantify the dose difference between pencil beam scanning proton therapy(PBSPT)and intensity-modulated 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 4 mm and 8 mm 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 genera-ted,and the single irradiation dose of these two plans was 200 cGy.The AIP PBSPT plans were registered to the end-in-spiration(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 EBT3 film,to evaluate the plan-ning robustness though the paired t test and the rank sum test.Results As the amplitude of motion increased,the IMRT△V(100)median values in T0 and T50 were-7.15％and-7.50％,the PBSPT △V(100)median values were-18.45％and-16.10％.The IMRT △(VR-VTR)median values in T0 and T50 were-37.09 and-38.03 cm3,the PBSPT △(VR-VTR)median values were-3.80 and-2.27 cm3.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)8 mm were higher than DSC4 mm in all ima-ges,and the difference were statistically significant,with t values of-2.666,-3.674,and-24.648,and P values of 0.045,0.014,and＜0.001,respectively.The PBSPT sensitivity index(SI)8 mm were lower than those of SI4 mm in AIP and plain CT images,the difference were statistically significant,with Z values of-2.908 and-2.945,and P values of 0.004 and 0.003,respectively.The difference between homogeneous index(HI)4mm and HI8mm of PBSPT were statistical-ly significant,with t values of-4.134,-2.913,and-16.997,and P values of 0.009,0.004,and＜0.001,respec-tively.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.
motion targetproton therapyphoton therapyfour-dimensional CTdose distribution
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