ESTRO 2023 - Abstract Book

S562

Sunday 14 May 2023

ESTRO 2023

The accuracy of the ADC estimates is satisfactory (error <3%) but requires special attention to noise contamination. The latter depends on the setting used, including the choice of the coil, the elements combination and the noise correction strategy. A higher NSA can increase the precision but has little benefit on accuracy of ADC values. Potential errors in the calibration of the phantom or the temperature correction were not considered for this analysis.

Mini-Oral: Detectors & dose management

MO-0669 First in vivo proof-of-concept of nanodroplet-mediated ultrasound-based proton range verification B. Carlier 1 , G. Collado-Lara 2 , S. Heymans 3,4 , Y. Toumia 5 , L. Musetta 6 , G. Paradossi 5 , H. Vos 2 , K. Van Den Abeele 3 , J. D'hooge 4 , U. Himmelreich 6 , E. Sterpin 1,7 1 KU Leuven, Oncology, Leuven, Belgium; 2 Erasmus MC University Medical Center, Cardiology, Rotterdam, The Netherlands; 3 KU Leuven KULAK, Physics, Kortrijk, Belgium; 4 KU Leuven, Cardiovascular Sciences, Leuven, Belgium; 5 University of Rome Tor Vergata, Chemical Science and Technologies, Rome, Italy; 6 KU Leuven, Imaging and Pathology, Leuven, Belgium; 7 Particle Therapy Interuniversity Center, PARTICLE, Leuven, Belgium Purpose or Objective Uncertainties on the in vivo proton range prevent the realization of the full potential of proton beams. They are typically accounted for by irradiating larger volumes at therapeutic doses using robust optimization or safety margins. This results in considerable healthy tissue exposure, degrading the inherent benefits of proton therapy. Hence, there is an urgent need for tools to verify the proton range in vivo . Recently, we proposed phase-change ultrasound (US) contrast agents as potential in vivo radiation sensors, whereby nanodroplets convert in echogenic microbubbles upon interaction with the proton beam. Previously, we demonstrated detection of the proton range with submillimeter reproducibility in gel phantoms. In this contribution, we provide a first in vivo proof-of-concept of the technology in healthy rats. Materials and Methods Phase-change nanodroplets consisted of a perfluorobutane core and a polyvinyl alcohol shell and were quantified using 19F NMR spectroscopy (Avance II 400, Bruker). Proton irradiations were performed at the Cyclotron Resources Centre in UCLouvain. There, healthy female Sprague-Dawley rats were anaesthetized and intravenously injected with 200 µ mol/kg nanodroplets. Afterwards, the animals were positioned in the proton beam, while continuously imaging their liver with low pressure plane wave US (DiPhAS, Fraunhofer IBMT) as shown in figure 1 . Animal 1 was irradiated once with a collimated proton beam (6 mm slit) for 5 Gy at 62 MeV. Animals 2-4 underwent two irradiations of 5 Gy, the first at 49.7 MeV, the second at 62 MeV. Thereafter, animal 4 was injected with an additional 350 µ mol/kg nanodroplets and re-irradiated with 5 Gy protons at 62 MeV. Finally, the US images were processed using custom MATLAB algorithms to extract contrast maps.

Figure 1. Proton irradiation setup.

Results Online US imaging confirmed the ability to (i) trigger droplet vaporization in vivo using proton radiation and (ii) track the contrast generation during irradiation. The irradiations at varying energies illustrated an energy-dependent response, whereby microbubbles are generated much deeper in the animal’s body at higher energies as expected from the larger proton range ( figure 2 ). Finally, increasing the droplet concentration from 200 to 350 µ mol/kg, resulted in additional contrast signals, indicating room for improvement in terms of the nanodroplet dosing.