Measurement of the leakage radiation from linear accelerators in the backward direction for 4, 6, 10, 15, and 18 MV X-ray energies

被引:10
|
作者
Jaradat, Adnan K.
Biggs, Peter J. [1 ]
机构
[1] Harvard Univ, Sch Med, Massachusetts Gen Hosp, Dept Radiat Oncol, Boston, MA 02114 USA
[2] Univ Massachusetts, Dept Phys, Lowell, MA USA
来源
HEALTH PHYSICS | 2007年 / 92卷 / 04期
关键词
X rays; accelerators; medical; medical radiation; radiation protection;
D O I
10.1097/01.HP.0000252308.89839.7d
中图分类号
X [环境科学、安全科学];
学科分类号
08 ; 0830 ;
摘要
The x-ray leakage from the housing of a therapy x-ray source is regulated to be < 0.1% of the useful beam exposure at I m from the source. It is to be expected that the machine leakage in the backward direction would be less because the gantry and stand contain significant amounts of additional metal to attenuate the x rays. A reduction in head leakage in this direction will have a direct effect on the thickness of the shielding wall behind the linear accelerator. However, no reports have been published to date on measurements in this area. The x-ray leakage in the backward direction has been measured from linacs having energies of 4, 6, 10, 15, and 18 MV using a 100 cm(3) ionization chamber and Al2O3 dosimeters. The leakage was measured at nine different positions over the rear wall using a 3 X 3 matrix with a 1-m separation between adjacent horizontal and vertical points with either the leftmost or rightmost column aligned with the target and isocenter. In general, the leakage is less than the canonical value, hint the exact value depends on energy, gantry angle, and measurement position. There is significantly greater attenuation directly behind the gantry stand for all energies. Leakage at 10 MV for some positions exceeded 0.1%. Additionally, neutron leakage measurements were made for 10, 15, and 18 MV x-ray beams, using track-etch detectors. The average neutron leakage was less than 0.1% except for 18 MV, where neutron leakage was more than 0.1% of the useful beam at some positions. Health Phys. 92(4):387-395; 2007.
引用
收藏
页码:387 / 395
页数:9
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