Tatcher M, Bjärngard B E
Roger Williams Cancer Centre, Brown University, Providence, RI 02908.
Radiother Oncol. 1994 Oct;33(1):64-7. doi: 10.1016/0167-8140(94)90087-6.
The behavior of the head-scatter factor in shielded 6 and 25 MV X-ray beams from a Philips SL25 linear accelerator was investigated by measuring incident fluences by direct (in-air) and indirect (in-phantom) methods. It was found that perturbations in head-scatter produced by shielding blocks arranged to define a slit-shaped field are considerably less than 1% in unwedged beams, even when 80% of a 20 x 20 cm2 field is shielded. The results are independent of beam energy and orientation of the slit with respect to the collimator jaws. When a 60 degrees wedge is inserted, the head-scatter factor decreases by up to a few percent, depending on slit direction but not on energy. The contributions to head-scatter from the block tray and the shielding blocks are negligible.
通过直接（空气中）和间接（模体中）方法测量入射注量，研究了飞利浦SL25直线加速器产生的屏蔽6和25 MV X射线束中头部散射因子的行为。结果发现，即使屏蔽20×20 cm²射野的80%，在未加楔形滤过板的射束中，用于形成狭缝状射野的屏蔽块所产生的头部散射扰动也远小于1%。结果与射束能量以及狭缝相对于准直器钳口的方向无关。插入60度楔形滤过板时，头部散射因子会降低几个百分点，这取决于狭缝方向而非能量。块托架和屏蔽块对头部散射的贡献可忽略不计。
