Bangert M, Titt U, Ziegenhein P, Mohan R, Oelfke U
German Cancer Reseach Center DKFZ, Heidelberg.
UT MD Anderson Cancer Center, Houston, TX.
Med Phys. 2012 Jun;39(6Part16):3795. doi: 10.1118/1.4735485.
To explore the potential of beam angle optimization (BAO) for IMPT and compare fixed beamlines with gantries.
For three patients with challenging intracranial lesions, we generate reference IMPT treatment plans applying three manually selected beam orientations and treatment plans applying three optimized beam orientations considering five scenarios: (1) patients are in supine position and the treatment room features (1.a) a horizontal beamline, (1.b) a horizontal, 45°, and vertical beamline, (1.c) a gantry, (2) patients are in supine or seated position and the treatment room features (2.a) a horizontal beamline, or (2.b) a horizontal, 45°, and vertical beamline. We use a genetic algorithm that considers up to 1,400 non-coplanar candidate beams and evaluates 10,000 beam ensembles for one BAO. Beam orientations that may compromise the robustness of treatment plans are excluded before the optimization based on an objective measure of existing tissue heterogeneities.
The optimized beam ensembles exhibit certain similarities even though the sets of candidate beams differ significantly for the five scenarios. Compared to manually selected beam orientations, they provide improved OAR sparing and equivalent target coverage. Compared to one another, they yield comparable target conformity (deviations of the conformity number <1%), target homogeneity (standard deviations of the target dose <0.8 Gy), and sparing of OARs (deviations of average mean and maximum doses in OARs +/- 1 Gy). Using a gantry, however, the integral dose can be reduced by 5-15% compared to a horizontal beamline with patients in supine position. For the investigated cases comparable reductions can be achieved by also irradiating in seated position with a horizontal, 45°, and vertical beamline.
BAO has the potential to provide beneficial IMPT treatment plans. Compared to fixed beamlines, gantries yield only modest effects regarding OAR sparing but may enable a significant reduction of integral dose for individual patients.
探讨调强质子治疗（IMPT）中射束角度优化（BAO）的潜力，并比较固定束线与龙门架的效果。
对于三名患有具有挑战性的颅内病变患者，我们生成了应用三种手动选择射束方向的参考IMPT治疗计划，以及考虑五种情况应用三种优化射束方向的治疗计划：（1）患者处于仰卧位，治疗室具有（1.a）水平束线，（1.b）水平、45°和垂直束线，（1.c）龙门架；（2）患者处于仰卧位或坐位，治疗室具有（2.a）水平束线，或（2.b）水平、45°和垂直束线。我们使用一种遗传算法，该算法考虑多达1400条非共面候选射束，并为一次BAO评估10000个射束组合。在优化之前，基于现有组织异质性的客观测量，排除可能损害治疗计划稳健性的射束方向。
尽管五种情况下的候选射束集有显著差异，但优化后的射束组合仍表现出一定的相似性。与手动选择的射束方向相比，它们能更好地保护危及器官（OAR）并提供等效的靶区覆盖。相互比较时，它们产生的靶区适形度（适形数偏差<1%）、靶区均匀性（靶区剂量标准差<0.8 Gy）以及对OAR的保护（OAR中平均剂量和最大剂量的偏差±1 Gy）相当。然而，与患者处于仰卧位的水平束线相比，使用龙门架时积分剂量可降低5%-15%。对于所研究的病例，通过使用水平、45°和垂直束线在坐位进行照射也可实现类似的剂量降低。
BAO有潜力提供有益的IMPT治疗计划。与固定束线相比，龙门架在保护OAR方面效果有限，但可能使个别患者的积分剂量显著降低。
