Goulet M, Gingras L, Depauw N, Archambault L, Seco J, Beaulieu L
Centre Hospitalier Univ de Quebec (CHUQ), Quebec, Qc.
Massachusetts General Hospital (MGH), Boston, MA.
Med Phys. 2012 Jun;39(6Part28):3968. doi: 10.1118/1.4736192.
To ensure the quality assurance of small field, dynamic radiotherapy, we present and validate a radiation tracking system based on long scintillating fibers that allows for the real-time measurement of the position and energetic fluence of a small incident radiation field.
We aligned 60 parallel scintillating fibers on a thin grooved acrylic slab with a 100-cm source-to-fibers distance. Both ends of each scintillating fiber were coupled to clear optical fibers to enable light collection by a single CCD camera using an f/0.95, 50 mm focal length lens. Using a small, static photon radiation field of 2×2 cm of a Varian Clinac iX, we changed the interaction position on the prototype using the linac treatment couch. The interaction position parallel and perpendicular to the scintillating fiber array were deduced using the optical attenuation of the scintillating fibers. The energetic fluence of the incident field was calculated from the fibers light fluxes, corrected for the position dependent optical attenuation and scintillation efficiency.
Considering a treatment couch positioning error of ±0.5 mm, the system was able to measure the field position with a mean error of 0.1 mm perpendicular and 0.8 mm parallel to the scintillating fiber array. The maximum error measured using this setup was of 0.13 mm perpendicular and 3.2 mm parallel to the scintillating fiber array. The energetic fluence was determined with a mean error of 0.5% and a maximum error of 2.2%.
This work demonstrates the capacity of a long scintillating fibers array to detect in real-time both the position and the energetic fluence of an incident small radiation field. Such methodology would allow for the real-time tracking of small field in both photon and particle radiation therapy.
为确保小射野动态放射治疗的质量保证，我们展示并验证了一种基于长闪烁光纤的放射跟踪系统，该系统能够实时测量小入射放射野的位置和能量注量。
我们将60根平行的闪烁光纤排列在一块带有细槽的薄丙烯酸板上，源到光纤的距离为100厘米。每根闪烁光纤的两端都与透明光纤耦合，以便使用一个f/0.95、50毫米焦距的镜头通过单个电荷耦合器件（CCD）相机进行光收集。使用瓦里安Clinac iX的2×2厘米小静态光子放射野，我们通过直线加速器治疗床改变原型上的相互作用位置。利用闪烁光纤的光衰减推导出与闪烁光纤阵列平行和垂直的相互作用位置。根据光纤光通量计算入射野的能量注量，并针对位置相关的光衰减和闪烁效率进行校正。
考虑到治疗床定位误差为±0.5毫米，该系统能够测量野的位置，垂直于闪烁光纤阵列的平均误差为0.1毫米，平行于闪烁光纤阵列的平均误差为0.8毫米。使用此设置测量的最大误差为垂直于闪烁光纤阵列0.13毫米，平行于闪烁光纤阵列3.2毫米。确定能量注量的平均误差为0.5%，最大误差为2.2%。
这项工作证明了长闪烁光纤阵列能够实时检测入射小放射野的位置和能量注量。这种方法将允许在光子和粒子放射治疗中实时跟踪小射野。
