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Energy spectra of 6 and 10 MV flattened and flattening filter-free photon beams from Varian Edge(PDF)

《中国医学物理学杂志》[ISSN:1005-202X/CN:44-1351/R]

Issue:
2018年第9期
Page:
997-1004
Research Field:
医学放射物理
Publishing date:

Info

Title:
Energy spectra of 6 and 10 MV flattened and flattening filter-free photon beams from Varian Edge
Author(s):
HAN Junjie1;  CHEN Lixin2;  ZHU Jinhan2;  PAN Yi1;  LIANG Yu1; WANG Xuetao3;  ZHANG Bailin3;  ZOUWenchang1
1. Department of Radiation Oncology, Guangdong General Hospital, Guangzhou 510080, China; 2. State Key Laboratory of Oncology in South China/Department of Radiation Oncology, Sun Yat-sen University Cancer Center, Guangzhou 510060, China; 3. Department of Radiation Oncology, Guangdong Traditional Chinese Medicine Hospital, Guangzhou 510120, China
Keywords:
Keywords: photon beam;  energy spectrum;  flattening filter model;  flattening filter-free model;  Varian Edge;  EGSnrc
PACS:
R811.1
DOI:
DOI:10.3969/j.issn.1005-202X.2018.09.002
Abstract:
Abstract: Objective To study the energy spectra of 6 and 10MV flattening filter (FF) and flattening-filter-free (FFF) photon beams from Varian Edge and compare their differences. Methods Monte Carlo program package, EGSnrc/Beamnrc, was used to establish Varian Edge models, including 6 MV FF and FFF, 10 MV FF and FFF, and the corresponding phase space files were simulated. Then with the phase space as input source, DOSXYZnrc was applied to measure the dose distributions in water phantom which were compared the simulated results obtained with three-dimensional water tank. If the differences between measurement and simulation were within 1%, the phase space files were analyzed with Beamdp in order to obtain the energy spectra. The differences among those obtained energy spectra were also compared. Results The differences of percentage depth dose and off axis ratio between simulation and measurement were within 1%. Compared with that of FF model, the energy spectra of FFF model became softer. The mean energy of 6 MV FFF decreased from 1.587 MeV to 1.172 MeV, and the percentage of low-energy photon (≤1 MeV) increased from 41.06% to 60.04%. The mean energy of 10 MV FFF decreases from 2.796 MeV to 1.956 MeV, and the percentage of low-energy photon increased from 21.22% to 44.63%. In the same field, the energy spectra of FFF model had slight changes with the increase of off axis distance, but the energy fluence caused by per initial particle was 2 to 4 times of FF model. Meanwhile, compared with that of FF model, the energy fluence distribution of FFF model became uneven, with a raising unflatness F. The analysis on the energy spectra in different fields revealed that the scattering from FFF accelerator head was less. Conclusion This study provides valuable references for the comprehension about the physical characteristic of FFF photon beams.

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Last Update: 2018-09-28