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Acoustic Signal From the Bragg Peak for Range Verification in Proton Therapy

K Parodi

S Reinhardt1 , W Assmann1 , S Kellnberger2,3 , M Omar2,3 , A Fink1 , C Gaebisch4 , P Thirolf1 , M Moser5 , G Dollinger5 , G Sergiadis6 , V Ntziachristos2,3 , K Parodi1*, (1) Ludwig-Maximilians University, Chair for Medical Physics, Munich, (2) Technical University Munich, Chair for Biological Imaging, Munich, (3) Helmholtz Center Munich, Institute for Biological and Medical Imaging, Neuherberg, (4) Munich University of Applied Science, Institute for Micro- and Nano-technology, Munich, (5) Universitaet der Bundeswehr, Institute for Applied Physics and Instrumentation, Neubiberg, (6) Signal Processing and Biomedical Technology Unit, Aristotle University, Thessaloniki,


WE-D-BRF-2 Wednesday 11:00AM - 12:15PM Room: Ballroom F

Purpose: Range verification in ion beam therapy relies to date on nuclear imaging techniques which require complex and costly detector systems. A different approach is the detection of thermoacoustic signals that are generated due to localized energy loss of ion beams. Aim of this work is to study the feasibility of determining the ion range with sub-mm accuracy by use of high frequency ultrasonic (US) transducers and to image the Bragg peak by tomography.

Methods: A water phantom was irradiated by a pulsed 20 MeV proton beam with varying pulse intensity, length and repetition rate. The acoustic signal of single proton pulses was measured by different PZT-based US detectors (3.5 MHz and 10 MHz central frequencies). For tomography a 64 channel US detector array was used and moved along the ion track by a remotely controlled motor stage.

Results: A clear signal of the Bragg peak was visible for an energy deposition as low as 10¹² eV. The signal amplitude showed a linear increase with particle number per pulse and thus, dose. Range measurements were reproducible within +/- 20 micrometer and agreed well with Geant4 simulations. The tomographic reconstruction does not only allow to measure the ion range but also the beam spot size at the Bragg peak position.

Conclusion: Range verification by acoustic means is a promising new technique for treatment modalities where the tumor can be localized by US imaging. Further improvement of sensitivity is required to account for higher attenuation of the US signal in tissue, as well as lower energy density in the Bragg peak in realistic treatment cases due to higher particle energy and larger spot sizes. Nevertheless, the acoustic range verification approach could offer the possibility of combining anatomical US imaging with Bragg Peak imaging in the near future.

Funding Support, Disclosures, and Conflict of Interest: The work was funded by the DFG cluster of excellence Munich Centre for Advanced Photonics (MAP).

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