Petti P L, Siddon R L
Phys Med Biol. 1985 Sep;30(9):985-91. doi: 10.1088/0031-9155/30/9/010.
Some recently designed x-ray-producing accelerators are equipped with a single built-in wedge, and different 'effective' wedge angles are obtained by combining an open (unwedged) and a wedged field in the appropriate proportions. This paper describes a technique for determining these proportions from measured isodose distributions of the two component fields. Our data for the Philips SL/75 6 MV accelerator are compared with two existing theoretical models. One model, in which the beams are weighted by the ratio of the tangents of the effective and nominal wedge angles, agrees with the data to within 3 degrees over the range of effective wedge angles and square field sizes examined. The second and simpler model, in which the beams are weighted by the ratio of the wedge angles directly, results in errors of as much as 11 degrees. It is shown that both of these models are approximations to an exact theoretical solution which may be formulated in terms of one free parameter. This parameter may be interpreted physically as the ratio of the slopes of the central-axis depth-dose curves for the open and wedged fields.
一些最近设计的产生X射线的加速器配备了单个内置楔形板，通过以适当比例组合开放（无楔形）和楔形射野可获得不同的“有效”楔形角。本文描述了一种根据两个组成射野的实测等剂量分布来确定这些比例的技术。我们针对飞利浦SL/75 6兆伏加速器获得的数据与两个现有的理论模型进行了比较。一个模型中，射野按有效楔形角与标称楔形角正切值之比加权，在所研究的有效楔形角和方形射野尺寸范围内，该模型与数据的吻合度在3度以内。第二个更简单的模型中，射野按楔形角之比直接加权，会产生高达11度的误差。结果表明，这两个模型都是一个精确理论解的近似，该精确理论解可用一个自由参数来表述。这个参数在物理上可解释为开放射野和楔形射野中心轴深度剂量曲线斜率之比。
