Ultrasound-assisted investigation of photon triggered vaporization of poly(vinylalcohol) phase-change nanodroplets: A preliminary concept study with dosimetry perspective |
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| Institution: | 2. Department of Ultrasound, Army Medical University, Chongqing, China;3. Applied Physics Program, University of Michigan, Ann Arbor, USA;4. Department of Biomedical Engineering, University of Michigan, Ann Arbor, USA;5. Department of Periodontics and Oral Medicine, School of Dentistry, University of Michigan, Ann Arbor, USA;6. Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, USA;2. School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA;2. Department of Physics, KU Leuven Campus Kulak, Kortrijk, Belgium;3. Department of Radiation Oncology, Erasmus MC Cancer Institute, Rotterdam, The Netherlands;4. DoseVue, Diepenbeek, Belgium;5. Department of Cardiovascular Sciences, KU Leuven, Leuven, Belgium |
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| Abstract: | PurposeWe investigate the vaporization of phase-change ultrasound contrast agents using photon radiation for dosimetry perspectives in radiotherapy.MethodsWe studied superheated perfluorobutane nanodroplets with a crosslinked poly(vinylalcohol) shell. The nanodroplets' physico-chemical properties, and their acoustic transition have been assessed firstly. Then, poly(vinylalcohol)-perfluorobutane nanodroplets were dispersed in poly(acrylamide) hydrogel phantoms and exposed to a photon beam. We addressed the effect of several parameters influencing the nanodroplets radiation sensitivity (energy/delivered dose/dose rate/temperature). The nanodroplets-vaporization post-photon exposure was evaluated using ultrasound imaging at a low mechanical index.ResultsPoly(vinylalcohol)-perfluorobutane nanodroplets show a good colloidal stability over four weeks and remain highly stable at temperatures up to 78 °C. Nanodroplets acoustically-triggered phase transition leads to microbubbles with diameters <10 μm and an activation threshold of mechanical index = 0.4, at 7.5 MHz. A small number of vaporization events occur post-photon exposure (6MV/15MV), at doses between 2 and 10 Gy, leading to ultrasound contrast increase up to 60% at RT. The nanodroplets become efficiently sensitive to photons when heated to a temperature of 65 °C (while remaining below the superheat limit temperature) during irradiation.ConclusionsNanodroplets’ core is linked to the degree of superheat in the metastable state and plays a critical role in determining nanodroplet’ stability and sensitivity to ionizing radiation, requiring higher or lower linear energy transfer vaporization thresholds. While poly(vinylalcohol)-perfluorobutane nanodroplets could be slightly activated by photons at ambient conditions, a good balance between the degree of superheat and stability will aim at optimizing the design of nanodroplets to reach high sensitivity to photons at physiological conditions. |
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| Keywords: | Nanodroplets Ultrasound LINAC photons Dosimetry |
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