Ianiro Anna, Infusino Erminia, D'Andrea Marco, Marucci Laura, Farneti Alessia, Sperati Francesca, Cassano Bartolomeo, Ungania Sara, Soriani Antonella
Department of Medical Physics, IRCCS Regina Elena National Cancer Institute - IFO, Rome, Italy.
Department of Radiation Oncology, IRCCS Regina Elena National Cancer Institute - IFO, Rome, Italy.
J Med Phys. 2023 Apr-Jun;48(2):120-128. doi: 10.4103/jmp.jmp_82_22. Epub 2023 Jun 29.
In our institution, stereotactic radiosurgery of multiple brain metastases is performed with the CyberKnife® (CK) device, using fixed/Iris collimators. In this study, nineteen fixed/Iris plans were recalculated with the multileaf collimator (MLC), to assess if it is possible to produce plans with comparable dosimetric overall quality.
For consistent comparisons, MLC plans were re-optimized and re-normalized in order to achieve the same minimum dose for the total planning target volume (PTV). Conformation number (CN), homogeneity index (HI) and dose gradient index (DGI) metrics were evaluated. The dose to the brain was evaluated as the volume receiving 12 Gy (V) and as the integral dose (ID). The normal tissue complication probability (NTCP) for brain radionecrosis was calculated as a function of V.
The reoptimized plans were reviewed by the radiation oncologist and were found clinically acceptable according to the The American Association of Physicists in Medicine (AAPM) Task Group-101 protocol. However, fixed/Iris plans provided significantly higher CN (+8.6%), HI (+2.2%), and DGI (+44.0%) values, and significantly lower ID values (-35.9%). For PTV less than the median value of 2.58cc, fixed/Iris plans provided significantly lower NTCP values. On the other side, MLC plans provided significantly lower treatment times (-18.4%), number of monitor units (-33.3%), beams (-46.0%) and nodes (-21.3%).
CK-MLC plans for the stereotactic treatment of brain multi metastases could provide an important advantage in terms of treatment duration. However, to contain the increased risk for brain radionecrosis, it could be useful to calculate MLC plans only for patients with large PTV.
在我们机构，使用固定/虹膜准直器通过射波刀（CK）设备对多发脑转移瘤进行立体定向放射外科治疗。在本研究中，用多叶准直器（MLC）重新计算了19个固定/虹膜计划，以评估是否有可能生成剂量学总体质量相当的计划。
为进行一致的比较，对MLC计划进行重新优化和重新归一化，以使总计划靶体积（PTV）达到相同的最小剂量。评估适形数（CN）、均匀性指数（HI）和剂量梯度指数（DGI）指标。将脑剂量评估为接受12 Gy的体积（V）和积分剂量（ID）。根据V计算脑放射性坏死的正常组织并发症概率（NTCP）。
放射肿瘤学家对重新优化的计划进行了审查，根据美国医学物理学家协会（AAPM）任务组-101方案，这些计划在临床上是可接受的。然而，固定/虹膜计划提供了显著更高的CN（+8.6%）、HI（+2.2%）和DGI（+44.0%）值，以及显著更低的ID值（-35.9%）。对于PTV小于中位数2.58cc的情况，固定/虹膜计划提供了显著更低的NTCP值。另一方面，MLC计划提供了显著更短的治疗时间（-18.4%）、监测单位数量（-33.3%）、射束数量（-46.0%）和节点数量（-21.3%）。
用于脑多发转移瘤立体定向治疗的CK-MLC计划在治疗持续时间方面可能具有重要优势。然而，为控制脑放射性坏死风险增加，仅为PTV大的患者计算MLC计划可能是有用的。
