Thomas S J, Foster K R
Medical Physics Department, Addenbrooke's Hospital, Cambridge, UK.
Phys Med Biol. 1995 Sep;40(9):1421-33. doi: 10.1088/0031-9155/40/9/003.
If the jaws of a linear accelerator are moved under computer control during irradiation, dose distributions similar to those with wedge filters can be produced. Varian linear accelerators utilize this effect to give a 'dynamic wedge', using segmented treatment tables (STTs). An algorithm is described to generate the dose per monitor unit at any point in a beam, using the STT values. Dynamically wedged beams are modelled as the superposition of static asymmetric beams, using an algorithm based on beam data measured for symmetric beams. Predictions of wedge factors, depth doses and profiles generated using the algorithm are compared with measurements. Good agreement is found between predictions and measurements. The calculation time is typically 5 ms/dose point on a PC with a 486DX processor.
如果在照射过程中，直线加速器的准直器在计算机控制下移动，就能产生与使用楔形滤过器时相似的剂量分布。瓦里安直线加速器利用这一效应，通过分段治疗床（STT）来产生“动态楔形”。本文描述了一种算法，该算法利用STT值来生成射野中任意一点处的每监测单位剂量。使用基于对称射野测量的射野数据的算法，将动态楔形射野模拟为静态非对称射野的叠加。将使用该算法生成的楔形因子、深度剂量和剂量分布的预测结果与测量结果进行比较。预测结果与测量结果吻合良好。在配备486DX处理器的个人计算机上，计算时间通常为每个剂量点5毫秒。
