Program Information
Monte Carlo Study of the Influence of Energy Spectra, Mesh Size, High Z Element On Dose and PVDR Based On 1-D Heterogeneous Model and 3-D Mouse Head Phantom for Microbeam Radiation Therapy
H Lin*, Jia Jing,Liangfeng Xu, Hefei University of Technology, Hefei, Anhui
Presentations
SU-I-GPD-T-355 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To evaluate the influence of energy spectra, mesh sizes, high Z element on dose and PVDR in MRT based on 1-D analogy-mouse-head-model (1-D MHM) and 3-D mouse-head-CT-phantom (3-D MHCP) by Monte Carlo Simulation.
Methods: A Microbeam-Array-Source-Model was implemented into EGSnrc/DOSXYZnrc. The microbeam size is assumed to be 25μm, 50μm or 75μm in thickness and fixed 1mm in height with 200μm c-t-c. The energy spectra of ID17 ESRF and BMIT 05ID-2 CLS were investigated. The suitable mesh size was optimized. The PVDR in 1-D MHM and 3-D MHCP was calculated and compared with the homogeneous water phantom. The equivalent path method was evaluated. The arc influence of 3-D MHCP was also compared with the rectangle water phantom by filling it with the water material (3-D MHCWP).
Results: PVDR of the little lower BMIT@CLS spectrum is 2.4 times that of ID17@ESRF for the more decreased valley dose. The maximum acceptable mesh is 5µm for 25µm, and 10µm for 50µm and 75µm microbeams with 200µm c-t-c. Even a 500μm skull layer will make PVDR difference up to 62.5% for 1-D MHM. However this influence is limited (< 5%) as long as the homogeneous media locates a little far away (e.g. 600µm). The peak dose uniformity of 3-D MHCP at the same depth could be up to 8% at the scale of 1.85mm×1mm irradiation area, whereas that of 3-D MHCWP is less than 1%. The high Z element makes the dose uniformity enhance in target. The surface arc of 3-D MHCWP could affect the superficial PVDR (from 44% to 21% in 0.2mm depth), whereas this influence is limited for the more depth (<1%).
Conclusion: The lower energy spectrum is better to increase normal tissue tolerance. An idea dose calculation algorithm for MRT should try to include the influence of 3-D heterogeneous media.
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