Acoustic Modulation Enables Proton Detection With Nanodroplets at Body Temperature

Area of Science:

• Medical Physics
• Acoustics
• Nanotechnology

Background:

• Superheated nanodroplets (NDs) show promise for in vivo proton range verification.
• Perfluorobutane nanodroplets (PFB-NDs) are stable but require secondary particles for vaporization at body temperature, limiting precision.
• Lowering droplet pressure can reduce the radiation-induced vaporization threshold for direct proton response.

Purpose of the Study:

• To investigate the use of acoustic fields to modulate the pressure of PFB-NDs.
• To lower the proton sensitization threshold of PFB-NDs at body temperature for enhanced range verification.
• To enable direct proton response of PFB-NDs using acoustic modulation.

Main Methods:

• Simultaneous proton irradiation and sonication (1.1 MHz focused transducer) of PFB-NDs in a flow tube.
• Acoustic monitoring of ND vaporization using a linear array.
• Application of increasing peak negative pressures (PNPs) to assess sensitization.

Main Results:

• Sensitization to primary protons was achieved between 25 and 40 °C using acoustic PNPs (800 to 200 kPa).
• Sonication alone did not induce vaporization at tested PNPs.
• Direct proton response was confirmed at 37 °C with a PNP of 400 kPa.

Conclusions:

• Acoustic modulation effectively lowers the sensitization threshold of superheated nanodroplets.
• This technique enables direct proton response of PFB-NDs at body temperature.
• The findings support ultrasound-assisted in vivo proton range verification.