Purpose: X-ray induced Acoustic Computed Tomography (XACT) is a developing imaging modality with the purpose of dosimetry and tracking x-ray beams in vivo for in line verification during radiotherapy treatment. This modality can change the standard of care for cancer patients by allowing image-guided dose and beam path adjustments during irradiation for the first time. Current XACT images are of low resolution and low sensitivity due to energy and pulse-width limitations of current clinical LINACs. We propose the use of a LINAC with higher energy and quicker beam pulses, allowing for the realization of real time beam monitoring with high resolution XACT.
Methods: In MATLAB, the relationship between pulse width and signal generation efficiency was explored. Experimentally, a prototypical LINAC with a pulse width of 2us and ultrasound transducer were used to acquire promising signals of a lead plate. Further experiments with a 0.2us pulse width demonstrated an increase in the resolution and sensitivity.
Results: Simulation results illustrated the inversely proportional relationship between the LINAC pulse width and the generated initial pressure waves, while maintaining the delivered dose. This increased signal generation efficacy which will improve the imaging sensitivity of XACT. Experimental results showed an increase in initial pressure wave amplitude with shorter pulse widths, leading to an increase in SNR when imaging a lead plate target with a 500kHz transducer. Utilizing a higher frequency transducer with shorter pulse width was shown to be possible and the experiments with the 0.2us pulse width are ongoing with promising preliminary results, as expected from simulation work.
Conclusion: The resolution of XACT imaging and dose sensitivity can be increased by decreasing the beam pulse duration, allowing for real time, in vivo XACT beam tracking and dosimetry during radiotherapy. With this, XACT can actualize precision radiotherapy and improve patient outcomes.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the National Institute of Health (R37CA240806), American Cancer Society (133697 RSG 19 110 01 CCE). The authors would like to acknowledge the support from UCI Chao Family Comprehensive Cancer Center (P30CA062203)