Electron beam therapy at extended source-to-surface distance: a Monte Carlo investigation

被引:12
|
作者
O'Shea, Tuathan P. [1 ]
Foley, Mark J. [1 ]
Rajasekar, David [2 ]
Downes, Patrick A. [3 ]
van der Putten, Wil [2 ]
Moore, Margaret [2 ]
Shearer, Andrew [3 ]
机构
[1] Natl Univ Ireland Galway, Sch Phys, Med Phys Grp, Galway, Ireland
[2] Univ Hosp Galway, Dept Med Phys & Bioengn, Galway, Ireland
[3] Natl Univ Ireland Galway, Dept Informat Technol, Galway, Ireland
来源
关键词
electron beam; extended SSD; output factor; Monte Carlo; BEAMnrc;
D O I
10.1120/jacmp.v9i4.2811
中图分类号
R8 [特种医学]; R445 [影像诊断学];
学科分类号
1002 ; 100207 ; 1009 ;
摘要
Electron-beam therapy is used to treat superficial tumors at a standard 100 cm source-to-surface distance (SSD). However, certain clinical situations require the use of an extended SSD. In the present study, Monte Carlo methods were used to investigate clinical electron beams, at standard and non-standard SSDs, from a Siemens Oncor Avant Garde (Siemens Healthcare, Erlangen, Germany) linear accelerator (LINAC). The LINAC treatment head was modeled in BEAMnrc for electron fields 5 cm in diameter and 10 x 10 cm, 15 x 15 cm, and 20 x 20 cm; for 6 MeV, 9 MeV, and 12 MeV; and for 100 cm, 110 cm, and 120 cm SSD. The DOSXYZnrc code was used to calculate extended SSD factors and dose contributions from various parts of the treatment head. The main effects of extended SSD on water phantom dose distributions were verified by Monte Carlo methods. Monte Carlo-calculated and measured extended SSD factors showed an average difference of +/- 1.8%. For the field 5 cm in diameter, the relative output at extended SSD declined more rapidly than it did for the larger fields. An investigation of output contributions showed this decline was mainly a result of a rapid loss of scatter dose reaching the d(max) point from the lower scrapers of the electron applicator. The field 5 cm in diameter showed a reduction in dose contributions; the larger fields generally showed an increased contribution from the scrapers with increase in SSD. Angular distributions of applicator-scattered electrons have shown a large number of acute-angle electron tracks contributing to the output for larger field sizes, explaining the shallow output reduction.
引用
收藏
页码:57 / 67
页数:11
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