Galvin J M, Wallace R E, Bloch P, Cheng E
Phys Med Biol. 1980 Sep;25(5):903-11. doi: 10.1088/0031-9155/25/5/008.
A procedure has been developed for producing accurate computer-calculated dose distributions at the air-tissue boundaries for oblique incidence of a photon beam. Measurements of the dose distribution under conditions of tangential incidence are presented for a Siemens 6 MV linear accelerator. These measurements have been compared with calculated distributions using the standard Cunningham-Clarkson calculation technique. Based on this comparison, two changes are suggested for improving the accuracy of the calculation. The grid spacing for the calculation is decreased in order that the rapid dose variations that occur at the boundary may be better followed. Furthermore, the dose calculation scheme is modified to take into account the differences in the amount of electron build-up which occurs. An algorithm is presented for making this modification. Also, the calculated dose at the exit surface had to be modified to handle the deficit of scatter material behind the calculation points. The results of these changes are shown as a comparison of a typical chest wall irradiation treatment plan using two opposing tangential fields.
已开发出一种程序，用于在光子束斜入射时在空气 - 组织边界处生成精确的计算机计算剂量分布。给出了西门子6 MV直线加速器在切线入射条件下的剂量分布测量结果。已将这些测量结果与使用标准坎宁安 - 克拉克森计算技术得出的计算分布进行了比较。基于此比较，提出了两项改进计算准确性的更改。减小计算的网格间距，以便更好地跟踪边界处出现的快速剂量变化。此外，修改剂量计算方案以考虑所发生的电子积累量的差异。给出了进行此修改的算法。而且，必须修改出射表面处的计算剂量，以处理计算点后面散射材料的不足。这些更改的结果以使用两个相对切线野的典型胸壁照射治疗计划的比较形式呈现。
