Bar-Deroma R D, Bjärngard B E
Roger Williams Cancer Center, Brown University, Providence, Rhode Island 02908.
Med Phys. 1994 Jul;21(7):1043-7. doi: 10.1118/1.597346.
The wedge factor (WF) for an x-ray beam is defined as the ratio of doses with and without the wedge at a point on the central axis, in water. It is a function of depth d, field size s, and collimator setting c. It is demonstrated that WF can be calculated as WF(d,s,c) = WFairAw(d)Hw(c)/A0(d)H0(c), where WFair is a constant factor, namely, the ratio of the incident fluences measured "in air" with and without the wedge for reference conditions, e.g., at isocenter for a 10x10 cm2 collimator setting. Aw(d) and A0(d) are attenuation factors, and Hw(c) and H0(c) head-scatter factors, with and without the wedge and normalized to reference conditions. This expression is based on the approximation that the scatter factor is the same with and without the wedge. The field size, which affects the scatter factor, is therefore not an important variable for the wedge factor using this approach. The above relation has been evaluated at 6 and 25 MV for various depths (d < or = 25 cm) and field sizes (s < or = 25 cm) for built-in wedges (wedge angle approximately 60 degrees). The agreement was better than +/- 1.5%. This formulation of the wedge factor is easily implemented in calculations of dose and monitor settings.
X射线束的楔形因子（WF）定义为水模体中心轴上某点有楔形滤过板和无楔形滤过板时的剂量之比。它是深度d、射野大小s和准直器设置c的函数。结果表明，WF可按WF(d,s,c) = WFairAw(d)Hw(c)/A0(d)H0(c)计算，其中WFair是一个常数因子，即参考条件下（例如，对于10×10 cm2准直器设置在等中心处）有楔形滤过板和无楔形滤过板时“在空气中”测量的入射注量之比。Aw(d)和A0(d)是衰减因子，Hw(c)和H0(c)是有楔形滤过板和无楔形滤过板时并归一化到参考条件下的头部散射因子。该表达式基于散射因子在有楔形滤过板和无楔形滤过板时相同的近似。因此，影响散射因子的射野大小对于使用此方法的楔形因子而言不是一个重要变量。上述关系已在6和25 MV能量下针对各种深度（d≤25 cm）和射野大小（s≤25 cm）对内建楔形滤过板（楔形角约60度）进行了评估。一致性优于±1.5%。这种楔形因子的公式在剂量和监测设置计算中易于实现。
