Ultrasound based dosimetry for radiotherapy: In-vitro proof of principle

Advances in radiotherapeutic treatments and the ability to detect accidents due to equipment mishandling or malfunctioning require the development of on-line in-vivo dosimetry systems. Here, we propose to use ultrasound contrast agents (UCAs) as a possible candidate for such a system, based on the hypothesis that irradiation of UCAs will modify their visco-elastic and/or their geometric properties and consequently their ultrasonic response. The aim of this study is to provide a proof of principle in-vitro. Solutions of saline with several commercially available lipid-shelled UCAs were investigated and the agents were characterized using a through transmission set-up, before and after irradiation. Although the agents were not yet optimized for radiation sensitivity, Targestar-P showed a noticeable dose dependency of the magnitude of the jump in phase velocity and amplitude of the attenuation at resonance. These results confirm the hypothesis that the ultrasonic readout of UCAs can be correlated with the ionizing radiation dose delivered to the agents. This supports the concept of using ultrasound and UCAs as a potential tool for in-vivo dosimetry.