为质子治疗设计针对射束的计划靶区（PTV），以考虑摆位和射程不确定性。
A beam-specific planning target volume (PTV) design for proton therapy to account for setup and range uncertainties.
机构信息
Medical Physics Program, Graduate School of Biomedical Sciences, The University of Texas Health Science Center at Houston, TX, USA.
出版信息
Int J Radiat Oncol Biol Phys. 2012 Feb 1;82(2):e329-36. doi: 10.1016/j.ijrobp.2011.05.011. Epub 2011 Jun 22.
PURPOSE
To report a method for explicitly designing a planning target volume (PTV) for treatment planning and evaluation in heterogeneous media for passively scattered proton therapy and scanning beam proton therapy using single-field optimization (SFO).
METHODS AND MATERIALS
A beam-specific PTV (bsPTV) for proton beams was derived by ray-tracing and shifting ray lines to account for tissue misalignment in the presence of setup error or organ motion. Range uncertainties resulting from inaccuracies in computed tomography-based range estimation were calculated for proximal and distal surfaces of the target in the beam direction. The bsPTV was then constructed based on local heterogeneity. The bsPTV thus can be used directly as a planning target as if it were in photon therapy. To test the robustness of the bsPTV, we generated a single-field proton plan in a virtual phantom. Intentional setup and range errors were introduced. Dose coverage to the clinical target volume (CTV) under various simulation conditions was compared between plans designed based on the bsPTV and a conventional PTV.
RESULTS
The simulated treatment using the bsPTV design performed significantly better than the plan using the conventional PTV in maintaining dose coverage to the CTV. With conventional PTV plans, the minimum coverage to the CTV dropped from 99% to 67% in the presence of setup error, internal motion, and range uncertainty. However, plans using the bsPTV showed minimal drop of target coverage from 99% to 94%.
CONCLUSIONS
The conventional geometry-based PTV concept used in photon therapy does not work well for proton therapy. We investigated and validated a beam-specific PTV method for designing and evaluating proton plans.
目的
报告一种在不均匀介质中使用单野优化（SFO）为被动散射质子治疗和扫描束质子治疗进行治疗计划和评估的规划靶区（PTV）的显式设计方法。
方法和材料
通过射线追踪和移动射线线来推导质子束的特定光束 PTV（bsPTV），以在存在设置误差或器官运动时考虑组织未对准。在光束方向上，针对靶区的近端和远端表面计算了由于基于计算机断层扫描的射程估计不准确而导致的射程不确定性。然后基于局部异质性构建 bsPTV。因此，bsPTV 可以直接用作规划靶区，就像在光子治疗中一样。为了测试 bsPTV 的稳健性，我们在虚拟体模中生成了一个单野质子计划。引入了故意的设置和范围错误。在各种模拟条件下，基于 bsPTV 和常规 PTV 设计的计划之间比较了对临床靶区（CTV）的剂量覆盖。
结果
使用 bsPTV 设计的模拟治疗在保持 CTV 的剂量覆盖方面明显优于常规 PTV 计划。在存在设置误差、内部运动和范围不确定性的情况下，使用常规 PTV 计划时，CTV 的最小覆盖范围从 99%降至 67%。然而，使用 bsPTV 的计划显示出目标覆盖范围从 99%降至 94%的最小下降。
结论
光子治疗中使用的常规基于几何形状的 PTV 概念不适用于质子治疗。我们研究并验证了一种用于设计和评估质子计划的特定光束 PTV 方法。
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