Góra Joanna, Kuess Peter, Stock Markus, Andrzejewski Piotr, Knäusl Barbara, Paskeviciute Brigita, Altorjai Gabriela, Georg Dietmar
a Department of Radiation Oncology , Medical University of Vienna/AKH Wien , Vienna , Austria.
Acta Oncol. 2015;54(8):1166-74. doi: 10.3109/0284186X.2015.1028590. Epub 2015 Apr 8.
Anatomical changes in the head-and-neck (H&N) region during the course of treatment can cause deteriorated dose distributions. Different replanning strategies were investigated for volumetric modulated arc therapy (VMAT) and intensity-modulated proton therapy (IMPT).
For six H&N patients two repeated computed tomography (CT) and magnetic resonance (MR) (CT1/MR1 at week 2 and CT2/MR2 at week 4) scans were acquired additionally to the initial planning CT/MR. Organs-at-risk (OARs) and three targets (CTV70Gy, CTV63Gy, CTV56Gy) were delineated on MRs and transferred to respective CT data set. Simultaneously integrated boost plans were created using VMAT (two arcs) and IMPT (four beams). To assess the need of replanning the initial VMAT and IMPT plans were recalculated on repeated CTs. Furthermore, VMAT and IMPT plans were replanned on the repeated CTs. A Demon algorithm was used for deformable registration of the repeated CTs with the initial CT and utilized for dose accumulation. Total dose estimations were performed to compare ART versus standard treatment strategies.
Dosimetric evaluation of recalculated plans on CT1 and CT2 showed increasing OAR doses for both, VMAT and IMPT. The target coverage of recalculated VMAT plans was considered acceptable in three cases, while for all IMPT plans it dropped. Adaptation of the treatment reduced D2% for brainstem by 6.7 Gy for VMAT and by 8 Gy for IMPT, for particular patients. These D2% reductions were reaching 9 Gy and 14 Gy for the spinal cord. ART improved target dose homogeneity, especially for protons, i.e. D2% decreased by up to 8 Gy while D98% increased by 1.2 Gy.
ART showed benefits for both modalities. However, as IMPT is more conformal, the magnitude of dosimetric changes was more pronounced compared to VMAT. Large anatomic variations had a severe impact on treatment plan quality for both VMAT and IMPT. ART is justified in those cases irrespective of treatment modalities.
头颈部（H&N）区域在治疗过程中的解剖学变化会导致剂量分布恶化。针对容积调强弧形放疗（VMAT）和调强质子治疗（IMPT）研究了不同的重新计划策略。
对于6名头颈部患者，除了初始计划的CT/MR扫描外，还额外获取了两次重复的计算机断层扫描（CT）和磁共振成像（MR）扫描（第2周的CT1/MR1和第4周的CT2/MR2）。在MR图像上勾画出危及器官（OARs）和三个靶区（CTV70Gy、CTV63Gy、CTV56Gy），并将其转移到各自的CT数据集。使用VMAT（两个弧形）和IMPT（四束射束）创建同步整合加量计划。为了评估重新计划的必要性，在重复的CT图像上重新计算初始VMAT和IMPT计划。此外，在重复的CT图像上对VMAT和IMPT计划进行重新计划。使用Demon算法对重复的CT图像与初始CT图像进行可变形配准，并用于剂量累积。进行总剂量估计以比较自适应放疗（ART）与标准治疗策略。
对CT1和CT2上重新计算的计划进行剂量学评估显示，VMAT和IMPT的OAR剂量均增加。重新计算的VMAT计划的靶区覆盖在3例中被认为是可接受的，而所有IMPT计划的靶区覆盖均下降。对于特定患者，治疗调整使VMAT的脑干D2%降低了6.7 Gy，IMPT降低了8 Gy。脊髓的这些D2%降低分别达到9 Gy和14 Gy。ART改善了靶区剂量均匀性，尤其是对于质子，即D2%降低了多达8 Gy，而D98%增加了1.2 Gy。
ART对两种治疗方式均显示出益处。然而，由于IMPT的适形性更好，与VMAT相比，剂量学变化的幅度更为明显。大的解剖学变异对VMAT和IMPT的治疗计划质量都有严重影响。在这些情况下，无论治疗方式如何，ART都是合理的。
