Loshek D D, Keller K A
Radiation Oncology, Marshfield Clinic, Wisconsin 54449.
Med Phys. 1988 Jul-Aug;15(4):604-10. doi: 10.1118/1.596212.
A boundary factor technique for predicting beam profiles has been described by Chui and Mohan [Med. Phys. 13, 409 (1986)]. Boundary factors are calculated as the ratio of the intensity measured in the central plane of a collimated field to the intensity measured in the same location in a 40 X 40 cm field. However, significant discrepancies arise if these factors are applied to the 40 X 40 cm intensity function at off-axis points to predict the beam profile for independently collimated fields. These discrepancies are primarily due to the assumption that the 40 X 40 cm profile approximates an unperturbed intensity function that would exist in the absence of the collimators or scattering media. Two techniques to reduce the residual perturbation are presented. The resulting refined boundary factors allow further factoring so as to permit the calculation of beam profiles for any field size and offset from three discrete functions.
Chui和Mohan [《医学物理》13, 409 (1986)] 描述了一种用于预测射束轮廓的边界因子技术。边界因子计算为在准直射野中心平面测量的强度与在40×40 cm射野中相同位置测量的强度之比。然而，如果将这些因子应用于离轴点处的40×40 cm强度函数以预测独立准直射野的射束轮廓，就会出现显著差异。这些差异主要是由于假设40×40 cm轮廓近似于在没有准直器或散射介质的情况下会存在的未受扰动的强度函数。本文提出了两种减少残余扰动的技术。由此得到的改进后的边界因子允许进一步分解，从而可以根据三个离散函数计算任何射野尺寸和偏移的射束轮廓。
