Létourneau D, Pouliot J, Roy R
Centre Hospitalier Universitaire de Québec, Pavillon L'Hôtel-Dieu de Québec, Canada.
Med Phys. 1999 Dec;26(12):2555-61. doi: 10.1118/1.598793.
In planning stereotactic radiosurgery treatments, depth dose curves, profiles, and dose rate of treatment beams are difficult to obtain with conventional detectors because of loss of lateral electronic equilibrium and volume averaging. A scintillating detector with high spatial resolution and good reliability has been developed to overcome this problem. The miniature dosimeter consists of two identical radiation-resistant 10 m long silica optical fibers, each connected to an independent silicon photodiode. A small cylindrical polystyrene scintillator (3.9 mm3) is optically glued to the detection fiber. The light seen by the photodiode connected to this fiber arises from fluorescence of the scintillator and from the Cerenkov effect produced in silica. The reference signal produced by the fiber without scintillator is used to subtract the Cerenkov light contribution from the raw detector response. The sensitive volume of the scintillating detector is nearly water-equivalent and thus minimizes dose distribution perturbation in water. The miniature dosimeter has a spatial resolution comparable to the film-densitometer system. Profiles of 1 cm diam, 6 MV photon beam measured with both systems show very similar shapes. Furthermore, the use of photodiodes instead of photomultiplier tubes gives a better stability response and offers the possibility to perform absolute dosimetry.
在计划立体定向放射外科治疗时，由于横向电子平衡的丧失和体积平均效应，使用传统探测器很难获得治疗束的深度剂量曲线、剂量分布和剂量率。为克服这一问题，已开发出一种具有高空间分辨率和良好可靠性的闪烁探测器。这种微型剂量计由两根相同的抗辐射10米长石英光纤组成，每根光纤都连接到一个独立的硅光电二极管。一个小圆柱形聚苯乙烯闪烁体（3.9立方毫米）光学粘贴在探测光纤上。连接到该光纤的光电二极管所看到的光来自闪烁体的荧光以及石英中产生的切伦科夫效应。没有闪烁体的光纤产生的参考信号用于从原始探测器响应中减去切伦科夫光的贡献。闪烁探测器的灵敏体积几乎与水等效，因此可将水中剂量分布的扰动降至最低。该微型剂量计的空间分辨率与胶片密度计系统相当。用这两种系统测量的直径1厘米、6兆伏光子束的剂量分布显示出非常相似的形状。此外，使用光电二极管而非光电倍增管可提供更好的稳定性响应，并为进行绝对剂量测定提供了可能。
