Abstract

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Title:: Evaluating the effects of air gap on dose of spot scanning proton therapy using Monte Carlo simulation

Author(s):: CHEN Lei1; 2; YU Hang1; FU Yuchuan1; HAN Jifeng2; 1. Department of Radiation Oncology, West China Hospital, Sichuan University, Chengdu 610041, China2. Key Laboratory of Radiation Physics and Technology of the Ministry of Education/Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610064, China

Keywords:: Keywords: spot scanning proton therapy Monte Carlo simulation dose correction factor air gap range shifter Geant4

Abstract:: Abstract: Objective To explore the effects of air gap on the dose of spot scanning proton therapy by Monte Carlo simulation.Methods Monte Carlo program Geant4 platform was used to establish aspot scanning proton model at the end of beam nozzle when using range shifter, and the model was verified. In the cases of phantom beams with different energies, range shifters, spot sizes, spot numbers under different air gaps, the dose deposition in the water model was calculated, and the dose difference was analyzed using dose correction factor generated by integrated depth dose. Results Different air gaps resulted in dose loss, and the dose loss increased as the increase of air gap and decreased as increasing depth in the water phantom. For higher beam energy and the range shifter with a thinner water equivalent thickness, the dose loss was greater. The dose loss caused by the change of spot size and the small increase of spot number did not differ significantly with a single beam in the same case. Conclusion When the range shifter is used, the tumor is in the superficial, and the air gap is large, it is recommended to establish a dose correction factor database and apply it to the treatment planning system to correct the dose.