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目的研究在使用CadPlan/Helios系统进行调强计划的逆向优化过程中散射半径参数的变化对计划结果的影响。方法采用均质水等效矩形体模,在不同散射半径条件下观察靶区和正常组织界面上的剂量梯度随散射半径的变化。另取一鼻咽癌病例的CT资料,采用七野照射技术,比较在不同散射半径条件下靶区、脑干等器官经逆向优化后的剂量数据。结果用大散射半径优化可提高靶区与正常组织界面上的剂量梯度,采用动态MLC照射的剂量梯度甚至可以高于主光栏的剂量梯度。在用不同散射半径优化同一病例计划时,使用短散射半径将使优化界面上的实时DVH与最终三维剂量计算的DVH结果相差较大,说明采用大散射半径得到的优化结果能使靶区剂量更接近处方剂量和更好地保护靶区外组织。结论在逆向调强优化中应采用尽可能大的散射半径以获得更好的结果。
Aim To study the influence of the variation of the scattering radius parameters on the planned results in the reverse optimization of IMRT using CadPlan / Helios system. Methods The homogenous water equivalent rectangular phantom was used to observe the change of dose gradient with the scattering radius at the interface between the target and the normal tissue under different scattering radii. Another case of nasopharyngeal CT data, the use of seven field irradiation technology, under different scattering radius target area, brain stem and other organs after reverse optimization dose data. Results The large scattering radius optimization can increase the dose gradient at the interface between the target and normal tissues. The dose gradient using dynamic MLC irradiation can even be higher than the dose gradient of the main beam. Using different scattering radii to optimize the same case plan, the use of a short scattering radius will result in a large difference between the real-time DVH at the optimized interface and the DVH results calculated at the final three-dimensional dose, indicating that the optimization results using a large scattering radius can make the target dose more Close to the prescription dose and better protect the tissues outside the target. Conclusion The best possible results should be obtained by using as large a scattering radius as possible in reverse power optimization.