Background and Aims

The sharp energy deposition of a pulsed ion beam (ideally using short pulses of a few microseconds) results in thermoacoustic waves (ionoacoustics). Signals acquired at multiple positions could allow to infer the in-vivo dose, to localize the Bragg peak or be used for dosimetry. This study assesses dose reconstruction for a small-animal proton irradiator under FLASH conditions (94Gy/s instantaneous dose rate, at the Bragg peak, delivery duration below 200ms). Particular attention is paid to the reconstruction from transient waves emerging from millisecond-long proton pulses at clinical cyclotron facilities.

Methods

The ionoacoustic signals recorded by a realistic 32-element linear array were simulated in water, accounting for the sensor response and acquisition noise (Fig.1). 10ms square proton pulses (30ns rising/falling time and 50% duty cycle) were considered, giving rise to transient ionoacoustic emissions from the pulse edges. The array geometry and piezoelectric material thickness were optimized to improve the accuracy of 2D-dose reconstruction obtained from time-reversal method.

Results

Using the detection of transient ionoacoustic waves from millisecond proton pulses, the dose can be reconstructed (Fig.2.) under FLASH conditions. Optimizing the sensor response and number of pulses to average the signal, the error in the range can be reduced to as low as 0.5% (30µm).

Conclusions

This feasibility study shows that transient ionoacoustics-based dose reconstruction allows for accurate range verification at cyclotron accelerators, assuming dedicated pulsing structure. Thanks to the direct relation between dose and pressure, this method could be applied for in-vivo dosimetry.

Acknowledgements: ERC-725539, H2020-EU INSPIRE-730983, CALA

Background and Aims

The sharp energy deposition of a pulsed ion beam (ideally using short pulses of a few microseconds) results in thermoacoustic waves (ionoacoustics). Signals acquired at multiple positions could allow to infer the in-vivo dose, to localize the Bragg peak or be used for dosimetry. This study assesses dose reconstruction for a small-animal proton irradiator under FLASH conditions (94Gy/s instantaneous dose rate, at the Bragg peak, delivery duration below 200ms). Particular attention is paid to the reconstruction from transient waves emerging from millisecond-long proton pulses at clinical cyclotron facilities.

Methods

The ionoacoustic signals recorded by a realistic 32-element linear array were simulated in water, accounting for the sensor response and acquisition noise (Fig.1). 10ms square proton pulses (30ns rising/falling time and 50% duty cycle) were considered, giving rise to transient ionoacoustic emissions from the pulse edges. The array geometry and piezoelectric material thickness were optimized to improve the accuracy of 2D-dose reconstruction obtained from time-reversal method.

Results

Using the detection of transient ionoacoustic waves from millisecond proton pulses, the dose can be reconstructed (Fig.2.) under FLASH conditions. Optimizing the sensor response and number of pulses to average the signal, the error in the range can be reduced to as low as 0.5% (30µm).

Conclusions

This feasibility study shows that transient ionoacoustics-based dose reconstruction allows for accurate range verification at cyclotron accelerators, assuming dedicated pulsing structure. Thanks to the direct relation between dose and pressure, this method could be applied for in-vivo dosimetry.

Acknowledgements: ERC-725539, H2020-EU INSPIRE-730983, CALA