Storchi P, Woudstra E
Dr Daniel den Hoed Cancer Centre, Department of Clinical Physics, Rotterdam, The Netherlands.
Phys Med Biol. 1995 Apr;40(4):511-27. doi: 10.1088/0031-9155/40/4/003.
Beam models are proposed for the calculation of the dose in off-axis planes of rectangular photon fields, when the data set used in the treatment planning system is based on the simple storage model of Milan and Bentley. For open beams the model separates the off-axis ratio into an envelope profile and two boundary profiles. The envelope profile gives the field intensity of the maximal position of the jaws and has rotational symmetry. The boundary profiles describe the boundaries of the field actually formed by the jaws. In the case of a wedged beam, the model also separates the off-axis ratio into envelope profiles and boundary profiles. To determine these profiles for the non-wedge direction from open beam profiles, the wedge thickness is converted to an equivalent water thickness. In the case of an asymmetric field, the boundary profiles are shifted to the field centre. Results of calculation with these models have been compared with measurements and the simple multiplication of profiles, which has often been used with the Milan-Bentley model. The new models agree within a few per cent with the measurements and are a great improvement compared to the simple multiplication of profiles.
当治疗计划系统中使用的数据集基于米兰和本特利的简单存储模型时，提出了用于计算矩形光子野离轴平面剂量的射束模型。对于开放射束，该模型将离轴比分为包络轮廓和两个边界轮廓。包络轮廓给出了准直器最大位置处的射野强度，并且具有旋转对称性。边界轮廓描述了由准直器实际形成的射野边界。对于楔形射束，该模型同样将离轴比分为包络轮廓和边界轮廓。为了从开放射束轮廓确定非楔形方向的这些轮廓，将楔形厚度转换为等效水厚度。在不对称射野的情况下，边界轮廓向射野中心移动。已将这些模型的计算结果与测量结果以及通常与米兰 - 本特利模型一起使用的轮廓简单相乘进行了比较。新模型与测量结果的偏差在百分之几以内，与轮廓简单相乘相比有了很大改进。
