Francescon P, Kilby W, Noll J M, Masi L, Satariano N, Russo S
Department of Radiation Oncology, Ospedale Di Vicenza, I-36100 Vicenza, Italy.
Phys Med Biol. 2017 Feb 7;62(3):1076-1095. doi: 10.1088/1361-6560/aa5610. Epub 2016 Dec 29.
Monte Carlo simulation was used to calculate correction factors for output factor (OF), percentage depth-dose (PDD), and off-axis ratio (OAR) measurements with the CyberKnife M6 System. These include the first such data for the InCise MLC. Simulated detectors include diodes, air-filled microchambers, a synthetic microdiamond detector, and point scintillator. Individual perturbation factors were also evaluated. OF corrections show similar trends to previous studies. With a 5 mm fixed collimator the diode correction to convert a measured OF to the corresponding point dose ratio varies between -6.1% and -3.5% for the diode models evaluated, while in a 7.6 mm × 7.7 mm MLC field these are -4.5% to -1.8%. The corresponding microchamber corrections are +9.9% to +10.7% and +3.5% to +4.0%. The microdiamond corrections have a maximum of -1.4% for the 7.5 mm and 10 mm collimators. The scintillator corrections are <1% in all beams. Measured OF showed uncorrected inter-detector differences >15%, reducing to <3% after correction. PDD corrections at d > d were <2% for all detectors except IBA Razor where a maximum 4% correction was observed at 300 mm depth. OAR corrections were smaller inside the field than outside. At the beam edge microchamber OAR corrections were up to 15%, mainly caused by density perturbations, which blurs the measured penumbra. With larger beams and depths, PTW and IBA diode corrections outside the beam were up to 20% while the Edge detector needed smaller corrections although these did vary with orientation. These effects are most noticeable for large field size and depth, where they are dominated by fluence and stopping power perturbations. The microdiamond OAR corrections were <3% outside the beam. This paper provides OF corrections that can be used for commissioning new CyberKnife M6 Systems and retrospectively checking estimated corrections used previously. We recommend the PDD and OAR corrections are used to guide detector selection and inform the evaluation of results rather than to explicitly correct measurements.
使用蒙特卡罗模拟来计算射波刀M6系统输出因子（OF）、百分深度剂量（PDD）和离轴比（OAR）测量的校正因子。这些包括针对InCise多叶准直器的首批此类数据。模拟探测器包括二极管、充气微腔室、合成微金刚石探测器和点闪烁体。还评估了各个微扰因子。OF校正显示出与先前研究相似的趋势。对于5毫米固定准直器，在所评估的二极管模型中，将测量的OF转换为相应点剂量比的二极管校正介于 -6.1% 和 -3.5% 之间，而在7.6毫米×7.7毫米的多叶准直器射野中，这些值为 -4.5% 至 -1.8%。相应的微腔室校正为 +9.9% 至 +10.7% 和 +3.5% 至 +4.0%。对于7.5毫米和10毫米准直器，微金刚石校正的最大值为 -1.4%。在所有射束中，闪烁体校正均<1%。测量的OF显示未校正的探测器间差异>15%，校正后降至<3%。对于所有探测器，在d>d处的PDD校正<2%，除了IBA Razor，在300毫米深度处观察到最大4%的校正。射野内的OAR校正比射野外小。在射束边缘，微腔室OAR校正高达15%，主要由密度微扰引起，这会模糊测量的半影。对于更大的射野和深度，射束外的PTW和IBA二极管校正高达20%，而Edge探测器需要较小的校正，尽管这些校正确实会随方向变化。这些效应在大射野尺寸和深度时最为明显，此时它们主要由注量和阻止本领微扰主导。射束外的微金刚石OAR校正<3%。本文提供了可用于新射波刀M6系统调试以及回顾性检查先前使用的估计校正的OF校正。我们建议使用PDD和OAR校正来指导探测器选择并为结果评估提供信息，而不是明确校正测量值。
