摘要
目的:研究不同大小射野挡铅对高能电子束射野输出剂量的影响,并讨论不同源皮距的变化规律。方法:在医科达直线加速器上对标称能量4MeV~18MeV共六档高能电子束不同源皮距时测量各限光筒附加射野挡铅的输出因子。结果:因自动跟随限光筒的X线准直器的设置对各能量各限光筒不同,各标准限光筒野输出因子与射野变化无确定规律;它随能量增加而减小,小野6cm×6cm却相反。各限光筒加挡铅射野的输出在小野时变化较大,射野直径与能量射程的差别大小影响输出因子的变化快慢。对不同限光筒形成的相同挡铅射野因子对低能大限光筒值更大,高能相反。延长源皮距仍基本遵循以上3个结论,且延长源皮距更高能量较小射野的输出下降更迅速。
Objective: To evaluate the effect of different sized block on high electron beam. Methods: we measure the field output factors at 4 MeV-18 MeV nominal electron energies for 5 different applicators and different sized blocking fields at 95 cm-115 cm SSD on Elekta Precise linear accelerator and analyse relationships between output factors and field size for different energies. Results:① It shows there is no determined field-size dependence of output factors for standard applicators,because the X-ray jaw's setting varies from each energy and applicator in order to achieve uniform dose distribution of electron beam. ②The output of blocking field drcreases rapidly as the field size is reduced to a very small one.And when the field dimension is smaller than the range of electron, the output will be effected. ③The output factors for same size blocking field with different applicators become larger at lower energy and for larger applicator. ④The measurement at different SSD shows similar results,but the output at larger air gaps decreases more sharply at smaller field size and lower energies.
出处
《中国医学物理学杂志》
CSCD
2005年第6期703-706,共4页
Chinese Journal of Medical Physics
关键词
电子束
输出因子
直线加速器
electron beam
output factors
linear accelerator