Mitigation of interplay effects with layer repainting techniques in intensity-modulated proton therapy for early-stage non-small cell lung cancer / 中华放射肿瘤学杂志

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 V 5Gy and V 20Gy 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 V 20Gy 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.