Purpose: One of the potential applications capitalizing on the thermoacoustic phenomenon is X-ray acoustic computed tomography (XACT), which utilizes acoustic waves generated by clinical X-ray beams. The field of XACT has garnered growing interest as a potential tool for in vivo dosimetry at no extra radiation. This study aims to investigate the feasibility of using XACT as a relative dosimetry tool without the use of markers.
Methods: XA signals generated from an X-ray beam in water were collected by a single element ultrasound transducer (Fig. 1a). The XA signal was amplified by a 60-dB preamplifier and acquired on an oscilloscope with 1024 averaging. The beam was delivered by a Varian TrueBeam system at 10 or 6 MV flattening filter free (FFF) energy with 4-µs pulse duration. To capture the change in X-ray dose with increasing water depth, the height of the transducer was varied from 2.60 cm to 13.00 cm at multi-millimeter steps. The peak-to-peak amplitude of the beam edge XA signal was plotted against transducer depth, and the XACT image was reconstructed in MATLAB using the back-projection method after high-pass filtering.
Results: XA signals from the near and far edges of the beam corresponding to the field size are identified (Fig. 1b). As the transducer depth is increased, the signal amplitude decreases, while the signal profile remains largely unchanged (Fig. 2a). Fig. 2b demonstrates the linear relationship between the near-edge XA signal amplitude and transducer depth, which is comparable to the percentage depth dose (PDD) curves of 10 and 6 MV beams. A reconstruction of the depth plane is shown in Fig. 3, with the edges of the beam visible at 4 cm apart.
Conclusion: This study demonstrates the feasibility of relative dosimetry using XACT imaging. Further investigation for a robust method to quantify XA signals is warranted.