Zeverino Michele, Jaccard Maud, Patin David, Ryckx Nick, Marguet Maud, Tuleasca Constantin, Schiappacasse Luis, Bourhis Jean, Levivier Marc, Bochud Francois O, Moeckli Raphaël
Institute of Radiation Physics, Lausanne University Hospital, Lausanne, Switzerland.
Department of Neurosurgery and Gamma Knife Center, Lausanne University Hospital, Lausanne, Switzerland.
Med Phys. 2017 Feb;44(2):355-363. doi: 10.1002/mp.12052. Epub 2017 Jan 30.
The Leksell Gamma Knife (LGK) Icon has been recently introduced to provide Gamma Knife technology with frameless stereotactic treatments which use an additional cone-beam CT (CBCT) imaging system and a motion tracking system (IFMM, Intra-Fraction Motion Management). The system was commissioned for the treatment unit itself as well as the imaging system.
The LGK Icon was calibrated using an A1SL ionization chamber. EBT3 radiochromic films were employed to independently check the machine calibration, to measure the relative output factors (ROFs) and to collect dose distributions. Coincidence between CBCT isocenter and radiological focus was evaluated by means of EBT3 films. CBCT image quality was investigated in terms of spatial resolution, contrast-to-noise ratio (CNR), and uniformity for the two presets available (low dose and high dose). Computed Tomography Dose Index (CTDI) was also measured for both presets.
The absolute dose rate of the LGK Icon was 3.86 ± 0.09 Gy/min. This result was confirmed by EBT3 readings. ROF were found to be 0.887 ± 0.035 and 0.797 ± 0.032 for the 8 mm and 4 mm collimators, respectively, which are within 2% of the Monte Carlo-derived ROF values. Excellent agreement was found between calculated and measured dose distribution with the gamma pass rate >95% of points for the nine dose distributions analyzed with 3%/1 mm criteria. CBCT isocenter was found to be within 0.2 mm with respect to radiological focus. Image quality parameters were found to be well within the manufacturer's specifications with the high-dose preset being superior in terms of CNR and uniformity. CTDI values were 2.41 mGy and 6.32 mGy, i.e. -3.6% and 0.3% different from the nominal values for the low-dose and high-dose presets, respectively.
The LGK Icon was successfully commissioned for clinical use. The use of the EBT3 to characterize the treatment unit was demonstrated to be feasible. The CBCT imaging system operates well within the manufacturer's specifications and provides good geometrical accuracy.
最近推出了Leksell伽玛刀（LGK）Icon，为伽玛刀技术提供无框架立体定向治疗，该治疗使用额外的锥形束CT（CBCT）成像系统和运动跟踪系统（IFMM，分次内运动管理）。该系统已针对治疗单元本身以及成像系统进行了调试。
使用A1SL电离室对LGK Icon进行校准。采用EBT3放射变色胶片独立检查机器校准、测量相对输出因子（ROF）并收集剂量分布。通过EBT3胶片评估CBCT等中心与放射焦点之间的重合度。针对两种可用预设（低剂量和高剂量），从空间分辨率、对比度噪声比（CNR）和均匀性方面研究CBCT图像质量。还测量了两种预设的计算机断层扫描剂量指数（CTDI）。
LGK Icon的绝对剂量率为3.86±0.09 Gy/分钟。EBT3读数证实了该结果。对于8毫米和4毫米准直器，ROF分别为0.887±0.035和0.797±0.032，在蒙特卡洛推导的ROF值的2%以内。对于以3%/1毫米标准分析的九个剂量分布，计算剂量分布与测量剂量分布之间的伽玛通过率>95%的点具有极好的一致性。发现CBCT等中心相对于放射焦点在0.2毫米以内。发现图像质量参数完全在制造商的规格范围内，高剂量预设在CNR和均匀性方面更优。CTDI值分别为2.41 mGy和6.32 mGy，即低剂量和高剂量预设分别与标称值相差-3.6%和0.3%。
LGK Icon已成功调试用于临床。证明使用EBT3表征治疗单元是可行的。CBCT成像系统在制造商的规格范围内运行良好，并提供良好的几何精度。
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