Radiation Medicine Research Center, Department of Radiation Oncology, Rigshospitalet, Copenhagen, Denmark.
Acta Oncol. 2011 Aug;50(6):777-83. doi: 10.3109/0284186X.2011.584555.
The purpose of this study was to compare treatment plans generated using fixed beam Intensity Modulated photon Radiation Therapy (IMRT), inversely optimized arc therapy (RapidArc(R), RA) with spot-scanned Intensity Modulated Proton Therapy (IMPT) for high-grade glioma patients. Plans were compared with respect to target coverage and sparing of organs at risk (OARs), with special attention to the possibility of hippocampus sparing.
Fifteen consecutive patients diagnosed with grade III and IV glioma were selected for this study. The target and OARs were delineated based on computed tomography (CT), FDG-positron emission tomography (PET) and T1-, T2-weigted, and Diffusion Tensor Imaging (DTI) magnetic resonance imaging (MRI) and fiber-tracking. In this study, a 6 MV photon beam on a linear accelerator with a multileaf collimator (MLC) with 2.5 mm leaves and a spot-scanning proton therapy machine were used. Two RA fields, using both a coplanar (clinical standard) and a non-coplanar, setup was compared to the IMRT and IMPT techniques. Three and three to four non-coplanar fields where used in the spot-scanned IMPT and IMRT plans, respectively. The same set of planning dose-volume optimizer objective values were used for the four techniques. The highest planning priority was given to the brainstem (maximum 54 Gy) followed by the PTV (prescription 60 Gy); the hippocampi, eyes, inner ears, brain and chiasm were given lower priority. Doses were recorded for the plans to targets and OARs and compared to our clinical standard technique using the Wilcoxon signed rank test.
The PTV coverage was significantly more conform for IMPT than the coplanar RA technique, while RA plans tended to be more conform than the IMRT plans, as measured by the standard deviation of the PTV dose. In the cases where the tumor was confined in one cerebral hemisphere (eight patients), the non-coplanar RA and IMPT techniques yielded borderline significantly lower doses to the contralateral hippocampus compared to the standard (22% and 97% average reduction for non-coplanar RA and IMPT, respectively). The IMPT technique allowed for the largest healthy tissue sparing of the techniques in terms of whole brain doses and to the fiber tracts. The maximum doses to the chiasm and brainstem were comparable for all techniques.
The IMPT technique produced the most conform plans. For tumors located in the one of the cerebral hemispheres, the non-coplanar RA and the IMPT techniques were able to reduce doses to the contralateral hippocampus. The IMPT technique offered the largest sparing of the brain and fiber tracts. RA techniques tended to produce more conform target doses than IMRT.
本研究旨在比较使用固定束强度调制光子放射治疗（IMRT）、逆向优化弧形治疗（RapidArc（RA））和点扫描强度调制质子治疗（IMPT）为高级别神经胶质瘤患者生成的治疗计划。这些计划在靶区覆盖和危及器官（OARs）保护方面进行了比较，特别关注海马体保护的可能性。
选择了 15 名连续诊断为 III 级和 IV 级神经胶质瘤的患者进行本研究。靶区和 OARs 根据计算机断层扫描（CT）、氟脱氧葡萄糖正电子发射断层扫描（PET）以及 T1、T2 加权、扩散张量成像（DTI）磁共振成像（MRI）和纤维追踪进行描绘。在本研究中，使用配备多叶准直器（MLC）的 6 MV 光子直线加速器和点扫描质子治疗机。比较了两种 RA 场，一种是共面（临床标准），另一种是非共面，同时还比较了 IMRT 和 IMPT 技术。点扫描 IMPT 和 IMRT 计划分别使用三个和三个到四个非共面场。四种技术都使用相同的一组计划剂量-体积优化目标值。脑干（最大 54 Gy）是最高的计划优先级，其次是 PTV（处方 60 Gy）；海马体、眼睛、内耳、大脑和视交叉的优先级较低。记录了计划到靶区和 OARs 的剂量，并使用 Wilcoxon 符号秩检验与我们的临床标准技术进行比较。
与共面 RA 技术相比，IMPT 对 PTV 的覆盖更符合标准，而 RA 计划比 IMRT 计划更符合标准，这可以通过 PTV 剂量的标准差来衡量。在肿瘤局限于一个大脑半球的情况下（8 名患者），非共面 RA 和 IMPT 技术与标准技术相比，对对侧海马体的剂量降低具有边缘显著意义（非共面 RA 和 IMPT 分别为 22%和 97%的平均降低）。从整个大脑剂量和纤维束的角度来看，IMPT 技术在保护健康组织方面是最有效的。视交叉和脑干的最大剂量在所有技术中是可比的。
IMPT 技术生成的计划最符合标准。对于位于大脑半球之一的肿瘤，非共面 RA 和 IMPT 技术能够降低对侧海马体的剂量。IMPT 技术对大脑和纤维束的保护作用最大。RA 技术比 IMRT 技术更倾向于产生更符合靶区剂量的计划。
