- •Monte Carlo study of a realistic mouse head phantom for Microbeam Radiation Therapy.
- •Different results from large phantom, e.g. Zubal head phantom, are obtained.
- •General Monte Carlo code EGSnrc/DOSXYZnrc is adapted to model microbeam array source.
- •Two SR energy spectra are studied by EGSnrc low energy physical models and cross sections.
- •Different results for the lower energy spectrum are obtained.
To evaluate the influence of energy spectra, mesh sizes, high Z element on dose and PVDR in Microbeam Radiation Therapy (MRT) based on 1-D analogy-mouse-head-model (1-D MHM) and 3-D voxel-mouse-head-phantom (3-D VMHP) by Monte Carlo simulation.
A Microbeam-Array-Source-Model was implemented into EGSnrc/DOSXYZnrc. The microbeam size is assumed to be 25 μm, 50 μm or 75 μm in thickness and fixed 1 mm in height with 200 μm c-t-c. The influence of the energy spectra of ID17@ESRF and BMIT@CLS were investigated. The mesh size was optimized. PVDR in 1-D MHM and 3-D VMHP was compared with the homogeneous water phantom. The arc influence of 3-D VMHP filled with water (3-D VMHWP) was compared with the rectangle phantom.
PVDR of the lower BMIT@CLS spectrum is 2.4 times that of ID17@ESRF for lower valley dose. The optimized mesh is 5 µm for 25 µm, and 10 µm for 50 µm and 75 µm microbeams with 200 µm c-t-c. A 500 μm skull layer could make PVDR difference up to 62.5% for 1-D MHM. However this influence is limited (<5%) for the farther homogeneous media (e.g. 600 µm). The peak dose uniformity of 3-D VMHP at the same depth could be up to 8% for 1.85 mm × 1 mm irradiation field, whereas that of 3-D VMHWP is <1%. The high Z element makes the dose uniformity enhance in target. The surface arc could affect the superficial PVDR (from 44% to 21% in 0.2 mm depth), whereas this influence is limited for the more depth (<1%).
An accurate MRT dose calculation algorithm should include the influence of 3-D heterogeneous media.
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Published online: September 22, 2017
Accepted: July 7, 2017
Received in revised form: July 5, 2017
Received: April 5, 2017
© 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.