Antony Rachitha, Herschtal Alan, Todd Stephen, Phillips Claire, Haworth Annette
Department of Physical Sciences, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia.
Department of Biostatistics, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia.
Australas Phys Eng Sci Med. 2017 Jun;40(2):433-439. doi: 10.1007/s13246-017-0551-5. Epub 2017 May 2.
A system for stabilising and monitoring eye movements for linac-based stereotactic radiotherapy associated with the mobile eye, the Eye Tracker, was developed. Whilst the Eye Tracker design is based on a previously reported system, the purpose of this study was to confirm that the modified version can be used with clinically acceptable treatment margins. We report the estimates of the margin required to account for inter- and intra-fraction eye motion based on data from 12 consecutive patients treated with the Eye Tracker system in place. Patients were immobilised in a head and neck mask and were required to fixate on a light source. A camera system monitored eye movements relative to CT simulation baseline measurements. The Exactrac system (Brainlab, Feldkirchen, Germany) combined with the Varian TrueBeamSTx (Varian Medical Systems, Palo Alto, CA) confirmed pre- and intra-treatment setup of the head position. Displacement/rotation of the image of the pupil/iris was determined in the lateral and superior-inferior directions using a video display. A standard margin equation was applied to estimate the margin required to account for inter- and intra-fraction eye movement. The average displacement in both directions was 0.1-0.2 mm (0.36 mm SD). All patients maintained a position within 1 mm of the intended position during treatment. Based on a Bayesian estimation of the systematic and treatment errors, accounting for displacements in two-planes and a standard deviation of the penumbral width of 1.3 mm, the estimated margins to achieve coverage of the GTV with the 95% isodose in 90% of patients was found to be less than 1 mm. Small random and systematic uncertainties due to inter- and intra-fraction movement of the eye were achieved with the Eye Tracker. Whilst the estimated margins are small (<1 mm) they need to be considered in addition to contouring and treatment delivery uncertainties.
开发了一种用于基于直线加速器的立体定向放射治疗中稳定和监测与活动眼球相关的眼球运动的系统，即眼动追踪器。虽然眼动追踪器的设计基于先前报道的系统，但本研究的目的是确认改进版本可用于临床可接受的治疗边界。我们根据12例连续使用眼动追踪器系统治疗的患者的数据，报告了考虑分次间和分次内眼球运动所需边界的估计值。患者被固定在头颈面罩中，并被要求注视一个光源。一个摄像系统监测相对于CT模拟基线测量的眼球运动。Exactrac系统（德国费尔德kirchen的Brainlab公司）与Varian TrueBeamSTx（加利福尼亚州帕洛阿尔托的Varian医疗系统公司）相结合，确认了治疗前和治疗中头部位置的设置。使用视频显示器在横向和上下方向确定瞳孔/虹膜图像的位移/旋转。应用标准边界方程来估计考虑分次间和分次内眼球运动所需的边界。两个方向上的平均位移为0.1 - 0.2毫米（标准差0.36毫米）。所有患者在治疗期间保持在预期位置1毫米范围内。基于对系统误差和治疗误差的贝叶斯估计，考虑到两个平面的位移以及半影宽度1.3毫米的标准差，发现90%的患者中用95%等剂量线覆盖GTV所需的估计边界小于1毫米。眼动追踪器实现了由于眼球分次间和分次内运动引起的小随机和系统不确定性。虽然估计的边界很小（<1毫米），但除了轮廓勾画和治疗实施的不确定性外，还需要考虑这些边界。
