Simulation of dosimetry impact of 4DCT uncertainty in 4D dose calculation for lung SBRT
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RESEARCH
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Simulation of dosimetry impact of 4DCT uncertainty in 4D dose calculation for lung SBRT Gang Liu1,2†, Fala Hu3†, Xuanfeng Ding4, Xiaoqiang Li4, Qihong Shao5, Yuenan Wang6, Jing Yang2 and Hong Quan1*
Abstract Background: Due to the heterogeneity of patient’s individual respiratory motion pattern in lung stereotactic body radiotherapy (SBRT), treatment planning dose assessment using a traditional four-dimensional computed tomography (4DCT_traditional) images based on a uniform breathing curve may not represent the true treatment dose delivered to the patient. The purpose of this study was to evaluate the accumulated dose discrepancy between based on the 4DCT_traditional and true 4DCT (4DCT_true) that incorporated with the patient’s real entire breathing motion. The study also explored a novel 4D robust planning strategy to compensate for such heterogeneity respiratory motion uncertainties. Methods: Simulated and measured patient specific breathing curves were used to generate 4D targets motion CT images. Volumetric-modulated arc therapy (VMAT) was planned using two arcs. Accumulated dose was obtained by recalculating the plan dose on each individual phase image and then deformed the dose from each phase image to the reference image. The “4 D dose” (D4D) and “true dose” (Dtrue) were the accumulated dose based on the 4DCT_traditional and 4DCT_true respectively. The average worse case dose discrepancy (ΔD) between D4D and Dtrue in all treatment fraction was calculated to evaluate dosimetric /planning parameters and correlate them with the heterogeneity of respiratory-induced motion patterns. A novel 4D robust optimization strategy for VMAT (4D Ro-VMAT) based on the probability density function(pdf) of breathing curve was proposed to improve the target coverage in the presence of heterogeneity respiratory motion. The data were assessed with a paired t-tests. Results: With increasing breathing amplitude from 5 to 20 mm, target ΔD99 , ΔD95 increased from 1.59,1.39 to 10.15%,8.66% respectively. When the standard deviation of breathing amplitude increased from 15 to 35% of the mean amplitude, ΔD99 , ΔD95 increased from 4.06,3.48 to 10.25%,6.63% respectively. The 4D Ro-VMAT plan significantly improve the target dose compared to VMAT plan. Conclusion: When the breathing curve amplitude is more than 10 mm and standard deviation of amplitude is higher than 25% of mean amplitude, special care is needed to choose an appropriated dose accumulation approach to evaluate lung SBRT plan target coverage robustness. The proposed 4D Ro_VMAT strategy based on the pdf of patient specific breathing curve could effectively compensate such uncertainties.
* Correspondence: [email protected] † Gang Liu and Fala Hu contributed equally to this work. 1 Key Laboratory of Artificial Micro- and Nano- structures of Ministry of Education and Center for Electronic Microscopy, School of Physics and Technology, Wuhan University, Wuhan 430072, China Full list of author information is available at the end of the article © The Author(s
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