Kertzscher Gustavo, Beddar Sam
Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
Phys Med Biol. 2016 Nov 7;61(21):7744-7764. doi: 10.1088/0031-9155/61/21/7744. Epub 2016 Oct 14.
We tested the potential of ruby inorganic scintillation detectors (ISDs) for use in brachytherapy and investigated various unwanted luminescence properties that may compromise their accuracy. The ISDs were composed of a ruby crystal coupled to a poly(methyl methacrylate) fiber-optic cable and a charge-coupled device camera. The ISD also included a long-pass filter that was sandwiched between the ruby crystal and the fiber-optic cable. The long-pass filter prevented the Cerenkov and fluorescence background light (stem signal) induced in the fiber-optic cable from striking the ruby crystal, which generates unwanted photoluminescence rather than the desired radioluminescence. The relative contributions of the radioluminescence signal and the stem signal were quantified by exposing the ruby detectors to a high-dose-rate brachytherapy source. The photoluminescence signal was quantified by irradiating the fiber-optic cable with the detector volume shielded. Other experiments addressed time-dependent luminescence properties and compared the ISDs to commonly used organic scintillator detectors (BCF-12, BCF-60). When the brachytherapy source dwelled 0.5 cm away from the fiber-optic cable, the unwanted photoluminescence was reduced from >5% to <1% of the total signal as long as the ISD incorporated the long-pass filter. The stem signal was suppressed with a band-pass filter and was <3% as long as the source distance from the scintillator was <7 cm. Some ruby crystals exhibited time-dependent luminescence properties that altered the ruby signal by >5% within 10 s from the onset of irradiation and after the source had retracted. The ruby-based ISDs generated signals of up to 20 times that of BCF-12-based detectors. The study presents solutions to unwanted luminescence properties of ruby-based ISDs for high-dose-rate brachytherapy. An optic filter should be sandwiched between the ruby crystal and the fiber-optic cable to suppress the photoluminescence. Furthermore, we recommend avoiding ruby crystals that exhibit significant time-dependent luminescence.
我们测试了红宝石无机闪烁探测器（ISD）在近距离放射治疗中的应用潜力，并研究了各种可能影响其准确性的有害发光特性。这些ISD由与聚甲基丙烯酸甲酯光纤电缆和电荷耦合器件相机耦合的红宝石晶体组成。该ISD还包括一个夹在红宝石晶体和光纤电缆之间的长波通滤光片。长波通滤光片可防止光纤电缆中产生的切伦科夫光和荧光背景光（干信号）照射到红宝石晶体上，因为这会产生不需要的光致发光而不是所需的放射发光。通过将红宝石探测器暴露于高剂量率近距离放射治疗源来量化放射发光信号和干信号的相对贡献。通过在屏蔽探测器体积的情况下用光纤电缆照射来量化光致发光信号。其他实验研究了随时间变化的发光特性，并将ISD与常用的有机闪烁探测器（BCF-12、BCF-60）进行了比较。当近距离放射治疗源距离光纤电缆0.5厘米时，只要ISD包含长波通滤光片，不需要的光致发光就会从总信号的>5%降低到<1%。通过带通滤光片抑制干信号，只要源到闪烁体的距离<7厘米，干信号就<3%。一些红宝石晶体表现出随时间变化的发光特性，在照射开始后10秒内以及源缩回后，红宝石信号变化>5%。基于红宝石的ISD产生的信号高达基于BCF-12的探测器的20倍。该研究提出了针对高剂量率近距离放射治疗中基于红宝石的ISD有害发光特性的解决方案。应在红宝石晶体和光纤电缆之间夹一个光学滤光片以抑制光致发光。此外，我们建议避免使用表现出明显随时间变化发光的红宝石晶体。
