SUPERHEATED DROP DETECTORS FOR DOSIMETRY IN RADIOTHERAPY

Summary

Principal Investigator: R Nath
Abstract: 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.
Funding Period: 1995-05-01 - 2007-01-31
more information: NIH RePORT