Ultrasound-assisted investigation of photon triggered vaporization of poly(vinylalcohol) phase-change nanodroplets: A preliminary concept study with dosimetry perspective

Toumia, Y.;Miceli, R.;Domenici, F.;Heymans, S.V.;Paradossi, G.;et.al.
(2021) Physica Medica : an international journal devoted to the applications of physics to medicine and biology — Vol. 89, p. 232-242 (2021)

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Authors
  • Toumia, Y.
    Author
  • Miceli, R.
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  • Domenici, F.
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  • Heymans, S.V.
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  • Sterpin, EdmondUCLouvain
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  • Paradossi, G.
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Abstract
Purpose: We investigate the vaporization of phase-change ultrasound contrast agents using photon radiation for dosimetry perspectives in radiotherapy. Methods: We 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. Results: Poly(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. Conclusions: Nanodroplets’ 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. © 2021 Associazione Italiana di Fisica Medica
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Toumia, Y., Miceli, R., Domenici, F., Heymans, S. V., Carlier, B., Cociorb, M., Oddo, L., Rossi, P., D’Angellilo, R. M., Sterpin, E., D’Agostino, E., Van Den Abeele, K., D’hooge, J., & Paradossi, G. (2021). Ultrasound-assisted investigation of photon triggered vaporization of poly(vinylalcohol) phase-change nanodroplets: A preliminary concept study with dosimetry perspective. Physica Medica : an international journal devoted to the applications of physics to medicine and biology, 89, 232-242. https://doi.org/10.1016/j.ejmp.2021.08.006 (Original work published 2021)