Gustafsson A, Lind B K, Svensson R, Brahme A
Karolinska Institutet, Stockholm, Sweden.
Med Phys. 1995 Jul;22(7):1141-56. doi: 10.1118/1.597507.
A very flexible iterative method for simultaneous optimization of dynamic multileaf collimation, scanning patterns and compensation filters has been developed. The algorithm can account for and optimize almost all the degrees of freedom available in a modern radiation therapy clinic. The method has been implemented for three dimensional treatment planning. The algorithm has been tested for a number of cases where both traditional wedge filters and block collimators, and modern equipment such as scanned beams and multileaf collimators are available. It is shown that the algorithm can improve heavily on traditional uniform dose plans with respect to the probability of achieving tumor control without causing severe complications (P+) simply by finding the optimal beam weights and block collimator settings. By allowing more complex equipment to deliver the dose and by accounting for their increased flexibility during the optimization, the dose plan can be substantially improved with respect to the applied objective functions. It is demonstrated that flexible lateral collimation combined with compensators or scanned beams in most cases allow close to optimal dose delivery. Here both the calculation time and the amount of primary computer memory needed has been reduced by performing the dose calculations in a cone beam coordinate system allowing the use of approximately spatially invariant energy deposition kernels. A typical calculation time for optimization of a two-field technique in a three dimensional volume is about 20 s per iteration step on a Hewlett-Packard 735 workstation. A well converged solution is normally obtained within about 50-100 iterations or within 15-30 min.
已开发出一种非常灵活的迭代方法，用于同时优化动态多叶准直、扫描模式和补偿滤过器。该算法可以考虑并优化现代放射治疗诊所中几乎所有可用的自由度。该方法已应用于三维治疗计划。该算法已在多种情况下进行测试，在这些情况下，既有传统的楔形滤过器和挡块准直器，也有现代设备，如扫描束和多叶准直器。结果表明，该算法只需找到最佳射束权重和挡块准直器设置，就能在不引起严重并发症（P+）的情况下，大幅提高实现肿瘤控制概率的传统均匀剂量计划。通过允许更复杂的设备输送剂量，并在优化过程中考虑其增加的灵活性，可以根据应用的目标函数显著改善剂量计划。结果表明，在大多数情况下，灵活的侧向准直与补偿器或扫描束相结合可实现接近最佳的剂量输送。通过在锥束坐标系中进行剂量计算，允许使用近似空间不变的能量沉积核，从而减少了计算时间和所需的主计算机内存量。在惠普735工作站上，对三维体积中的双野技术进行优化时，每次迭代步骤的典型计算时间约为20秒。通常在大约50 - 100次迭代或15 - 30分钟内可获得收敛良好的解。
