Rosenberg I, Chu J C, Saxena V
Department of Medical Physics, Rush Presbyterian St. Luke's Medical Center, Chicago, Illinois 60612.
Med Phys. 1995 Jan;22(1):55-61. doi: 10.1118/1.597524.
A simple approach was developed that calculates the output factors and tissue maximum ratio of an asymmetric field at any point within the open field, and specifically both at the central axis (when the jaws do not shadow it) and at the effective center of the open field, using the existing tables for symmetric fields and the multidepth profile information for the largest available field size (either open or with a wedge present). Day's method was adapted to calculate the effective values of the usual field-size-dependent parameters. This approach makes these parameters also dependent on the location of the calculation point relative to the field edges in an asymmetric field. This algorithm was tested by comparing its predictions with measurements of asymmetric and half blocked fields, with and without wedges, in a water phantom at different depths and off-axis distances. The agreement between calculated and measured dose rate is within 1%-3% even in highly asymmetric fields for both 6- and 18-MV photons.
开发了一种简单的方法，该方法使用对称野的现有表格和最大可用野尺寸（开放野或有楔形板）的多深度轮廓信息，计算开放野内任意点处不对称野的输出因子和组织最大剂量比，特别是在中心轴（当准直器不遮挡时）和开放野的有效中心处。采用戴氏方法计算通常与野尺寸相关的参数的有效值。这种方法使这些参数也取决于计算点在不对称野中相对于野边缘的位置。通过将其预测结果与在不同深度和离轴距离的水模中对有或无楔形板的不对称野和半阻挡野的测量结果进行比较，对该算法进行了测试。对于6兆伏和18兆伏光子，即使在高度不对称的野中，计算剂量率与测量剂量率之间的一致性也在1%-3%以内。
