An MCNPX2.7.0 study of Bragg peak degradation owing to density heterogeneity patterns for a CGMH therapeutic proton beam

作者：Chao Tsi Chian; Tsai Yi Chun; Chen Shih Kuan; Wu Shu Wei; Tung Chuan Jong; Hong Ji Hong; Wang Chun Chieh; Lee Chung Chi^*

来源：Radiation Physics and Chemistry, 2017, 137: 121-124.

DOI：10.1016/j.radphyschem.2016.01.014

• Monte Carlo
• Proton therapy
• Pencil beam
• Density heterogeneities
• Bragg peak degradation

The purpose of this study was to investigate the density heterogeneity pattern as a factor affecting Bragg peak degradation, including shifts in Bragg peak depth (Z(Bp)), distal range (R-80 and R-20), and distal fall-off (R-80-R-20) using Monte Carlo N-Particles, eXtension (MCNPX). Density heterogeneities of different patterns with increasing complexity were placed downstream of commissioned proton beams at the Proton and Radiation Therapy Centre of Chang Gung Memorial Hospital, including one 150 MeV wobbling broad beam (10 x 10 cm(2)) and one 150 MeV proton pencil beam (FWHM of cross-plane=2.449 cm, FWHM of in-plane=2.256 cm). MCNPX 2.7.0 was used to model the transport and interactions of protons and secondary particles in density heterogeneity patterns and water using its repeated structure geometry. Different heterogeneity patterns were inserted into a 21 x 21 x 20 cm(3) phantom. Mesh tally was used to track the dose distribution when the proton beam passed through the different density heterogeneity patterns. The results show that different heterogeneity patterns do cause different Bragg peak degradations owing to multiple Coulomb scattering (MCS) occurring in the density heterogeneities. A trend of increasing R20 and R-80-R-20 with increasing geometry complexity was observed. This means that Bragg peak degradation is mainly caused by the changes to the proton spectrum owing to MCS in the density heterogeneities. In contrast, R-80 did not change considerably with different heterogeneity patterns, which indicated that the energy spectrum has only minimum effects on R-80. Bragg peak degradation can occur both for a broad proton beam and a pencil beam, but is less significant for the broad beam.

• 出版日期2017-8
• 单位长春大学