Mitigation of interplay effects with layer repainting techniques in intensity-modulated proton therapy for early-stage non-small cell lung cancer
Shang Haijiao1, Pu Yuehu1, Liu Chenbin2, He Xiaodong3, Wang Yuenan4
1Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China; 2MAyo Clinic Arizona, Phoenix 85054, USA; 3Department of Radiation Oncology, Ruijin Hospital Affiliated to the Shanghai JiaoTong University, Shanghai 200025, China; 4National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen 518116, China
Abstract：Objective The purpose of current study was to evaluate the interplay effects in intensity-modulated proton therapy (IMPT) for lung cancer and compare the results of different Iso-energy layer repainting techniques in the mitigation of interplay effects. Methods Eight patients with lung cancer who underwent 4DCT were retrospectively selected. A robust CTV-based IMPT plan was generated for each based on commercial TPS, considering patient setup errors ±5 mm, range uncertainties ±3.5%, and CTV time structure motion in 4DCT image. Monte Carlo dose engines were used for all IMPT plans in the final dose calculation. The 4D static dose (4DSD) and 4D dynamic dose (4DDD) were calculated using a hybrid deformable algorithm and simulated proton delivery system for interplay effects. An index[ΔI(ROI,DVH)] was developed to quantitatively evaluate the interplay effects. We applied Iso-energy layer repainting techniques with different numbers of repainting (3, 4, 5, 6, 7) to the robust IMPT plans and evaluated the difference in the mitigation of interplay effects based on the ΔI(ROI,DVH)index. Results Due to interplay effects, the mean values of target coverage, conformity and homogeneity index reduced by 13.7%, 12.7% and 24.6%, respectively. The mean values of lung V5Gy and V20Gy improved by 0.8%,3.4% and 2.6%. Compared to the IMPT plans without layer repainting, Multiple iso-energy layers repainting techniques improved the mean values of CTV coverage by 4.5%,3.8%,3.8%,3.6% and 5.7%, respectively. The average values of lung V20Gy reduced by 1.5%,1.8%,1.7%,1.6% and 1.9%, respectively. Conclusions In the robust CTV-based IMPT plans, the interplay effects degraded the target dose distribution but were mitigated using iso-energy layer repainting techniques. We recommended to use the layer repainting technique according to the characteristics of the patient.
Shang Haijiao,Pu Yuehu,Liu Chenbin et al. Mitigation of interplay effects with layer repainting techniques in intensity-modulated proton therapy for early-stage non-small cell lung cancer[J]. Chinese Journal of Radiation Oncology, 2020, 29(9): 772-778.
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