Superheated Drop Detectors for Dosimetry in Radiotherapy

说明(申请人提供)：当悬浮在凝胶基质中的亚稳过热状态时，卤素微滴可用作辐射剂量计。当电离辐射穿过液滴的乳化液时，它会沿着释放的带电粒子的轨迹沉积能量。这会触发过热液滴的突然汽化，产生气泡，可以用视觉和/或电子手段检测到。基于气泡高分辨率磁共振成像的位置灵敏可重复使用探测器已发展成为三维光子剂量计。这种过热乳胶室(SEC)用于距离大于1厘米的1251近距离治疗源周围的剂量测量的可行性已经被证明。SEC提供了高空间精度和分辨率以及良好的光子能量依赖性的优势。SEC的一个独特优势是可以包含有关线性能量转移(LET)的信息，这可能有助于表征存在于组织与高原子序数材料(如金属支架、导丝、钙化等)的源和界面附近的低能量辐射的影响。直径类似于细胞大小(约10微米)的过热液滴提供了开发凝聚相微剂量计的潜力，这可能会导致一种新的工具，用于更好地了解辐射效应的机制。将开发一种微型SEC，用于毫米距离的高分辨率剂量测量，使用新的乳化和涂层方法以获得更均匀和更小的微滴，使用3D回波平面成像和光学层析成像的快速压力循环和高速图像采集的自动化技术将用于提高统计精度和空间分辨率。迷你SEC将用于确定与眼睛和血管内近距离治疗中使用的典型伽马和贝塔源之间几毫米距离的参考剂量学参数。我们将使用过热和气泡形成的理论模型来研究SEC确定低能光子的LET和界面效应的能力。SEC将被改装为使用压力阶跃的低能光子的LET光谱仪。为了测量高Z材料与组织界面的剂量，将开发一种类似培养皿的微型SEC，它能够测量约10 PM厚度的各层的平均剂量。

DESCRIPTION (provided by applicant): Microdroplets of halocarbons can serve as radiation dosimeters when maintained in a metastable superheated state suspended in a gel matrix. As ionizing radiation crosses the emulsion of droplets, it deposits energy along the tracks of released charged particles. This triggers the sudden vaporization of the superheated droplets, creating bubbles, which can be detected visually and/or electronically. A position sensitive reusable detector based on high resolution MR imaging of bubbles has been developed as a 3Dphoton dosimeter. The feasibility of using this superheated emulsion chamber (SEC) for dosimetry around a 1251brachytherapy source at distances larger than 1 cm has been demonstrated. The SEC offers the advantages of high spatial accuracy and resolution as well as good photon energy dependence. A unique advantage of the SEC is the possibility of including information about the linear energy transfer (LET) which may be of interest in characterizing the effects of low energy radiations that are present near the sources and near the interfaces of tissue with high atomic number materials, such as metallic stents, guide wires, calcifications, etc. The superheated droplets with diameters similar to cellular sizes (approximately 10 mum) provide the potential of developing a condensed-phase microdosimeter, which may lead to a new tool for better understanding the mechanisms of radiation effects. A mini SEC will be developed for high resolution dosimetry at millimeter distances using new emulsification and coating methods to achieve more uniform and smaller microdroplets An automated technique for rapid pressure cycling and high-speed image acquisition using 3D-echo planar imaging and optical tomography will be used to improve statistical accuracy and spatial resolution. The mini SEC will be used to determine reference dosimetry parameters at millimeter distances from typical gamma and beta sources used in ocular and intravascular brachytherapy. The ability of SEC for the determination of LET and interface effects for low energy photons will be investigated using a theoretical model of superheat and bubble formation. The SEC will be adapted to serve as an LET spectrometer for low energy photons using pressure steps. A Petri-dish-like micro SEC will be developed for the determination of doses at the interface of high Z materials and tissues with capability of measuring doses averaged over layers of about 10 pm thickness.