Division of Radiation Oncology, H. Lee Moffitt Cancer Center, Tampa, Florida 33612, USA.
J Appl Clin Med Phys. 2010 Jan 28;11(1):3169. doi: 10.1120/jacmp.v11i1.3169.
We performed an initial dosimetric evaluation of SmartArc - a novel VMAT planning module for Philips Pinnacle treatment planning system. A test suite of structure sets and dose objectives provided by the AAPM for multi-institutional comparison of IMRT dosimetry was used. A total of fifty plans were successfully delivered. The effect of control point spacing on dosimetric accuracy was investigated. When calculated with the 4 masculine spacing, the overall mean point dose errors measured with an ion chamber were 0.5+/-1.4 and -0.3+/-1.4% for the PTV and OAR, respectively. The gamma(3%,3mm) passing rate, measured for absolute dose with a biplanar diode array, was 98.2+/-1.6% (range 94.5-99.9%). Ninety percent of the passing rate values were above 97.7%. With the 6 masculine control point spacing, the highly modulated plans exhibited large dosimetric errors, while the results were still acceptable for the simpler cases. The data show that the practical accuracy of the small-arc approximation, which is at the heart of VMAT dose calculations, depends not only on the control point spacing, but also on the size and relative position of the MLC openings corresponding to the consecutive control points. The effect of the minimum allowed separation between the opposing leaves was found to be minimal. It appears that 4 masculine control point spacing may be a good compromise between calculation speed and accuracy. However each institution is encouraged to establish its own treatment planning guidelines based on the case complexity and acceptable error level.
我们对 SmartArc 进行了初步剂量评估 - 这是飞利浦 Pinnacle 治疗计划系统的一种新型 VMAT 计划模块。使用了 AAPM 为多机构 IMRT 剂量学比较提供的结构集和剂量目标测试套件。总共成功交付了五十个计划。研究了控制点间距对剂量准确性的影响。当使用 4 个控制点间距计算时，用离子室测量的总体平均点剂量误差分别为 PTV 和 OAR 的 0.5+/-1.4% 和 -0.3+/-1.4%。用双平面二极管阵列测量绝对剂量的伽马（3%，3mm）通过率为 98.2+/-1.6%（范围为 94.5-99.9%）。通过率值的 90%以上高于 97.7%。对于 6 个控制点间距，高度调制的计划表现出较大的剂量误差，但对于较简单的情况，结果仍然可以接受。数据表明，小弧逼近的实际精度（VMAT 剂量计算的核心）不仅取决于控制点间距，还取决于与连续控制点相对应的 MLC 开口的大小和相对位置。发现允许叶片对之间最小分离的影响最小。似乎 4 个控制点间距可能是计算速度和准确性之间的良好折衷。但是，每个机构都应根据病例复杂性和可接受的误差水平，制定自己的治疗计划指南。
