Prado Alejandro, Milanés Ana Isabel, Cabello Eduardo, Díaz Raúl, Ferrando Alejandro, Pozo Gustavo, Leonor Mario, Manzano Marta
Department of Medical Physics and Radiation Protection, University Hospital 12 de Octubre, Madrid, Spain.
J Med Phys. 2019 Jan-Mar;44(1):1-8. doi: 10.4103/jmp.JMP_56_18.
In the present study, the performance of four VMAT beam arrangements used for hippocampal-sparing whole-brain radiation therapy is addressed.
Data corresponding to 20 patients were utilized so as to generate plans for every beam configuration. A preliminary study was conducted to assess the optimal distance between optimization structures (PTVx) and hippocampi. V, V, D, D, D, homogeneity index (HI) and Paddick conformity factor (CF) were evaluated for PTV. D and D were considered for hippocampi. All plans were required to perform at least as recommended in RTOG 0933 trial regarding organs at risk (OAR) sparing and PTV objectives.
Considerable hippocampi sparing alongside with a reasonably low decrease in PTV coverage was achieved using a 7 mm distance between hippocampi and PTV optimization structure. Beam setup 3 (comprised of two full arcs with 0° couch angle and two half arcs with 90° couch angle) achieved the best PTV coverage, HI and CF, while it performed the second-best sparing in hippocampi and lenses. Moreover, beam setup 3 was the second-fastest treatment, although it resulted in the highest number of delivered MU among all beam setups. Beam setup 1 (comprised of two full arcs with no couch angles) was the fastest and it delivered a significantly less amount of monitor units compared with the other beam setups evaluated. Furthermore, a higher robustness was obtained by using no couch angles. Although beam setup 1 was the least optimal considering OAR sparing, it still performed better than required in the RTOG 0933 trial.
Overall, beam setup 3 was considered to be the best. It is worth mentioning that, apart from our results, the election of one of these beam arrangements might be dependent on the amount of patient workload at a specific institution.
在本研究中，探讨了用于海马体保留全脑放射治疗的四种容积调强弧形放疗（VMAT）射束布置的性能。
利用20例患者的数据为每种射束配置生成计划。进行了一项初步研究，以评估优化结构（PTVx）与海马体之间的最佳距离。对PTV评估了V、V、D、D、D、均匀性指数（HI）和帕迪克适形因子（CF）。对海马体评估了D和D。所有计划都要求在危及器官（OAR）保留和PTV目标方面至少达到RTOG 0933试验中的推荐标准。
海马体与PTV优化结构之间的距离为7 mm时，实现了可观的海马体保留，同时PTV覆盖的降低幅度合理。射束布置3（由两个0°治疗床角度的全弧和两个90°治疗床角度的半弧组成）实现了最佳的PTV覆盖、HI和CF，同时在海马体和晶状体的保留方面排名第二。此外，射束布置3是第二快的治疗方式，尽管它在所有射束布置中导致的输出跳数（MU）最多。射束布置1（由两个无治疗床角度的全弧组成）是最快的，与其他评估的射束布置相比，它输出的监测单位数量明显更少。此外，不使用治疗床角度可获得更高的稳健性。尽管考虑到OAR保留，射束布置1是最不理想的，但它仍比RTOG 0933试验中的要求表现更好。
总体而言，射束布置3被认为是最佳的。值得一提的是，除了我们的结果外，这些射束布置之一的选择可能取决于特定机构的患者工作量。
