Oldham M, Khoo V S, Rowbottom C G, Bedford J L, Webb S
Joint Department of Physics, Institute of Cancer Research and the Royal Marsden NHS Trust, Surrey, UK.
Phys Med Biol. 1998 Aug;43(8):2123-46. doi: 10.1088/0031-9155/43/8/010.
A treatment-planning case study has been performed on a patient with a medium-sized, convex brain tumour. The study involved the application of advanced treatment-plan optimization techniques to improve on the dose distribution of the 'standard plan' used to treat the patient. The standard plan was created according to conventional protocol at the Royal Marsden NHS Trust, and consisted of a three-field (one open and two wedged) non-coplanar arrangement, with field shaping to the beam's-eye view of the planning target volume (PTV). Three optimized treatment plans were created corresponding to (i) the optimization of the beam weights and wedge angles of the standard plan, (ii) the optimization of the beam orientations, beam weights and wedge angles of the standard plan, and (iii) a full fluence tomotherapy optimization of 1 cm wide (at isocentre), 270 degree arcs. (i) and (ii) were created on the VOXELPLAN research 3D treatment-planning system, using in-house developed optimization algorithms, and (iii) was created on the PEACOCK tomotherapy planning system. The downhill-simplex optimization algorithm is used, in conjunction with 'threshold-dose' cost-function terms enabling the algorithm to optimize specific regions of the dose-volume histogram (DVH) curve. The 'beam-cost plot' tool is presented as a visual aid to the selection of beneficial beam directions. The methods and pitfalls in the transfer of plans and patient data between the two planning systems are discussed. Each optimization approach was evaluated, relative to the standard plan, on the basis of DVH and dose statistics in the PTV and organs at risk (OARs). All three optimization approaches were able to improve on the dose distribution of the standard plan. The magnitude of the improvement was greater for the optimized beam-orientation and tomotherapy plans (up to 15% and 30% for the maximum and mean OAR doses). A smaller improvement was observed in the beam-weight and wedge-angle optimized plan (up to 5% and 10% in the maximum and mean OAR doses). In the tomotherapy plan, difficulty was encountered achieving an acceptable homogeneity of dose in the PTV. This was improved by treating the gross tumour volume (GTV) and (PTV - GTV) regions as separate targets in the inverse planning, with the latter region prescribed a slightly higher dose to reduce edge under-dosing. In conclusion, for the medium-sized convex tumour studied, the tomotherapy dose distribution showed a significant improvement on the standard plan, but no significant improvement over a conventional three-field plan where the beam orientations, beam weights and wedge angles had been optimized.
已对一名患有中等大小凸形脑肿瘤的患者进行了治疗计划案例研究。该研究涉及应用先进的治疗计划优化技术，以改善用于治疗该患者的“标准计划”的剂量分布。标准计划是根据皇家马斯登国民保健服务信托基金的传统方案制定的，由一个三野（一个开放野和两个楔形野）非共面排列组成，射野形状与计划靶区（PTV）的射野视角相匹配。创建了三个优化治疗计划，分别对应于：（i）标准计划的射束权重和楔形角优化；（ii）标准计划的射束方向、射束权重和楔形角优化；以及（iii）1厘米宽（等中心处）、270度弧的全通量断层放射治疗优化。（i）和（ii）是在VOXELPLAN研究型三维治疗计划系统上创建的，使用内部开发的优化算法，（iii）是在PEACOCK断层放射治疗计划系统上创建的。采用下山单纯形优化算法，并结合“阈值剂量”成本函数项，使算法能够优化剂量体积直方图（DVH）曲线的特定区域。展示了“射束成本图”工具，作为选择有益射束方向的视觉辅助工具。讨论了两个计划系统之间计划和患者数据传输中的方法及陷阱。基于PTV和危及器官（OARs）中的DVH和剂量统计数据，相对于标准计划对每种优化方法进行了评估。所有三种优化方法都能够改善标准计划的剂量分布。优化射束方向和断层放射治疗计划的改善幅度更大（最大和平均OAR剂量分别高达15%和30%）。在射束权重和楔形角优化计划中观察到的改善较小（最大和平均OAR剂量分别高达5%和10%）。在断层放射治疗计划中，在PTV中实现可接受的剂量均匀性遇到了困难。通过在逆向计划中将大体肿瘤体积（GTV）和（PTV - GTV）区域视为单独的靶区，对后者区域规定稍高的剂量以减少边缘剂量不足，情况得到了改善。总之，对于所研究的中等大小凸形肿瘤，断层放射治疗剂量分布相对于标准计划有显著改善，但与射束方向、射束权重和楔形角已优化的传统三野计划相比，没有显著改善。
