Superheated Drop Detectors for Dosimetry in Radiotherapy

描述（由申请人提供）：当卤化碳微滴悬浮在凝胶基质中保持亚稳态过热状态时，可以用作辐射剂量计。当电离辐射穿过液滴的乳剂时，它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蒸发，产生气泡，这些气泡可以通过视觉和/或电子方式检测到。研制了一种基于气泡高分辨率磁共振成像的位置敏感可重复使用探测器作为三维光子剂量计。在距离大于1cm的1251x近距离放射治疗源周围使用这种过热乳化液腔（SEC）进行剂量测定的可行性已经得到证实。SEC具有高空间精度和分辨率以及良好的光子能量依赖性的优点。SEC的一个独特优势是可以包含有关线性能量传递（LET）的信息，这可能对描述低能量辐射的影响很感兴趣，这些辐射存在于源附近和高原子序数材料的组织界面附近，如金属支架、导丝、钙化等。直径与细胞大小相似（约10 μ m）的过热液滴提供了开发冷凝相微剂量计的潜力，这可能导致更好地了解辐射效应机制的新工具。迷你SEC将用于毫米距离的高分辨率剂量测定，使用新的乳化和涂层方法来获得更均匀和更小的微滴。使用3d回波平面成像和光学断层扫描进行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将用于确定用于眼内和血管内近距离放射治疗的典型γ和β源在毫米距离上的参考剂量学参数。我们将使用过热和气泡形成的理论模型来研究SEC对低能光子的LET和界面效应的测定能力。SEC将被改造成使用压力步骤的低能光子LET光谱仪。将开发一种类似培养皿的微型SEC，用于测定高Z材料和组织界面处的剂量，具有测量约10pm厚度层上的平均剂量的能力。

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.