Abstract
This study proposes a novel alternative range-verification method for proton beam with acoustic waves generated from spherical metal markers. When proton beam is incident on metal markers, most of the resulting pressure waves are confined in the markers because of the large difference in acoustic impedance between the metal and tissue. However, acoustic waves with frequency equal to marker’s resonant frequency escape this confinement; the marker briefly acts as an acoustic transmitter. Herein, this phenomenon is exploited to measure the range of the proton beam. We test the proposed strategy in 3-D simulations, combining the dose calculations with modelling of acoustic-wave propagation. A spherical gold marker of 2.0 mm diameter was placed in water with a 60 MeV proton beam incident on it. We investigated the dependence of pressure waves on the width of beam pulse and marker position. At short beam pulse, specific high-frequency acoustic waves of 1.62 MHz originating from the marker were observed in wave simulations, whose amplitude correlated with the distance between the marker and Bragg peak. Results indicate that the Bragg peak position can be estimated by measuring the acoustic wave amplitudes from the marker, using a single detector properly designed for the resonance frequency.
Highlights
Spot-scanning proton therapy (SSPT) is an advanced form of proton therapy, and is being widely employed in newly constructed treatment centers[1]
Examples include positron-emission tomography (PET)[6], prompt gamma-ray (PG) detection[7] and detection of ionoacoustic wave, i.e., acoustic signals originating from the impact of proton beams[8]
Our wave-propagation simulations showed that resonant waves are emitted from the gold marker after the injection of the pulsed proton pencil beam
Summary
Spot-scanning proton therapy (SSPT) is an advanced form of proton therapy, and is being widely employed in newly constructed treatment centers[1]. Uncertainty in the range of the proton beam arises from multiple sources, including computed tomography (CT) number to stopping-power conversions and anatomical changes during radiation treatment. Uncertainty in the patient setup can be reduced by exploiting the image guidance techniques For this purpose, radiographically visible markers placed within or nearby the tumour are commonly employed to monitor the position of the tumour during radiation therapy[21,22,23]. Waves with the resonant frequency of the marker gain enough amplitude to propagate outward into the surrounding tissue We demonstrated this phenomenon in simulations of acoustic-wave transport to explore how this phenomenon can be applied to beam range verification
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