Department of Radiotherapy, Maria Skłodowska-Curie Memorial Cancer Center and Institute of Oncology, Gliwice Branch, Gliwice, Poland.
Radiat Oncol. 2013 Aug 23;8:205. doi: 10.1186/1748-717X-8-205.
Stereotactic irradiation of large or critically located arteriovenous malformations (AVMs) is a special challenge for clinicians and radiation physicists. To date, no comprehensive comparison of two linac-based radiosurgery systems used for hypofractionated radiotherapy of large AVMs was published. The aim of the study was to compare dose distributions between CyberKnife (CK) system and linac with a micro-multileaf collimator (L-mMLC) in high-grade or critically located cerebral AVMs.
Two sets of plans made for 15 different patients with at least 95% target coverage were selected for comparisons. Conformity (CI), homogeneity (HI) and gradient score (GSI) indices, conformity index proposed by Lomax (CIL), conformation number (CN), quality of coverage (Q), volumes of brain receiving 12,10,8,6,4, and 2 Gy, minimum and maximum doses for critical structures in both treatment planning systems (TPS) were compared. Finally, the number of monitor units needed to deliver the prescribed dose was compared.
The mean minimum doses in the target volume were 93.3% (CK) and 90.7% (L-mMLC),p=n.s, maximum: 119.7 and 110%, respectively (p=0.004). The mean CI was 1.46 and 1.86, HI: 1.2, and 1.11, CIL 0.7, and 0.6, CN: 0.68 and 0.58 for CK and mMLC, respectively (p<0.05). The values of GSI and Q were not significantly different. The volumes of the brain receiving low doses (4 Gy and 2 Gy) were significantly lower in the CK system. The number of monitor units necessary to deliver the prescribed dose was significantly greater in case of the CK system.
Better conformity can favor the CK system for treatment of large AVMs at the cost of higher maximum doses and worse homogeneity. L-mMLC is superior when shorter treatment time is required. Neither system can assure satisfying dose gradients outside large targets surrounded by numerous critical structures.
立体定向照射大型或关键部位动静脉畸形（AVM）对临床医生和放射物理学家来说是一个特殊的挑战。迄今为止，尚无关于两种用于大型 AVM 分次放射治疗的直线加速器放射外科系统的全面比较。本研究的目的是比较 CyberKnife（CK）系统和配备微多叶准直器（L-mMLC）的直线加速器在高级别或关键部位脑 AVM 中的剂量分布。
选择了 15 名患者的两套计划，这些患者的靶区覆盖率至少为 95%，用于比较。比较了两种治疗计划系统（TPS）的适形度（CI）、均匀度（HI）和梯度评分（GSI）指数、Lomax 提出的适形指数（CIL）、适形度指数（CN）、覆盖质量（Q）、接受 12、10、8、6、4 和 2 Gy 的脑体积、关键结构的最小和最大剂量，以及两种 TPS 中需要的监测器单位数。
靶区的平均最小剂量分别为 93.3%（CK）和 90.7%（L-mMLC），p=n.s，最大剂量分别为 119.7%和 110%（p=0.004）。平均 CI 分别为 1.46 和 1.86，HI：1.2 和 1.11，CIL 分别为 0.7 和 0.6，CN：0.68 和 0.58（CK 和 mMLC），p<0.05）。GSI 和 Q 的值无显著差异。CK 系统中大脑接受低剂量（4 Gy 和 2 Gy）的体积明显较低。CK 系统中需要的监测器单位数明显更高。
更好的适形度可以使 CK 系统更有利于治疗大型 AVM，但代价是更高的最大剂量和更差的均匀性。当需要较短的治疗时间时，L-mMLC 更具优势。在存在大量关键结构的大型靶区周围，两种系统都不能保证满意的剂量梯度。
