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Pencil Beam Dose Algorithm for Intensity Modulated Proton Therapy with Scanning Proton Beams

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H Wang

H Wang1,2,3, H Zheng1,2,3 , R Cao1,2,3 , J Jia1,2,3 , J Song1,2,3*, T He1,2,3 , Y Wu1,2,3, FDS Team, (1) Key Laboratory of Neutronics and Radiation Safety, Institute of Nuclear Energy Safety Technology, Chinese Academy of Sciences, Hefei, Anhui, 230031, China, (2) Anhui Radiotherapy Engineering Technology Research Center, Hefei Anhui 230031, China, (3) Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions,Su Zhou 215006, China


SU-I-GPD-T-111 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Accurate dose calculation plays a vital role in achieving the dosimetric advantage of intensity modulated proton therapy (IMPT). A pencil beam (PB) algorithm, which takes lateral inhomogeneity into special account to achieve high accuracy, was developed for the Accurate Radiation Therapy System (KylinRay-IMPT).

Methods: The pencil beam algorithm used “stopping power - lateral spread” model. Each pencil beam was transported along its mean direction; and the depth dose was derived with stopping power and range straggling of the radiated material which enabled effective treatment of longitudinal inhomogeneity, while lateral distribution was obtained using Fermi-Eyges theory. To better treat lateral inhomogeneity, a broad proton scanning beam was divided into multiple thinner pencil beams hexagonally distributed around the original beam center. It was found that this splitting method was more efficient than conventional orthogonal grid splitting. Furthermore, during the transport of each proton pencil beam, a proper weight averaging method was used to consider the stopping/scattering effects of all the materials within the pencil beam region, which was in contrast to conventional methods only considering materials on the central axis.

Results: The algorithm was benchmarked against Monte Carlo (MC) simulation with both homogeneous and heterogeneous phantoms to test its accuracy. Five beam energies, spanning the energy range with clinical interest, have been investigated. The maximum dose difference between the PB algorithm and MC result is about 2% for homogeneous cases, 3% for the heterogeneous cases, and planar dose gamma analysis yields pass rate of at least 98% with 2%/2mm criteria and 10% dose threshold.

Conclusion: A PB algorithm which explicitly took heterogeneities into account has been presented. The accuracy of the algorithm is tested and preliminarily verified, and further testing with clinical cases is underway.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by the National Natural Science Foundation of China (No.11605233).

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