Fifty-seventh annual meeting of the American association of physicists in medicine
TH-CD-304-06: Amplitude and Frequency Characteristics of Acoustic Waves Induced Following Radiotherapy Linear Accelerator Irradiation
To enhance understanding of the characteristics of acoustic waves induced following irradiation by a linac photon beam through experiments and simulations. Such waves have potential applications in in vivo dosimetry since their properties are related to the dose distribution following a single pulse of irradiation.
The acoustic waves induced following linac photon beam irradiation of different metal blocks suspended in a water tank were investigated. Experimentally, these waves were detected with an ultrasound transducer and amplification electronics. Computationally, the acoustic waves were modeled by combining Monte Carlo dose calculations and acoustic wave transport techniques. The effect of varying metal block size, material, depth, and linac photon beam energy on the amplitude and frequency of the induced acoustic signal was investigated.
Experimental and simulated acoustic waveforms indicated that increasing photon beam energy and decreasing metal block depth along the central axis increases signal amplitude by an amount proportional to the increased dose deposited in the block. Decreasing in-plane lead block width increased the frequency of acoustic waves due to the smaller dimension of the lead-induced perturbation in the global dose distribution. Varying the metal block material from lead to aluminum resulted in smaller amplitude acoustic waves due to aluminum's lower electron density, while aluminum's higher speed of sound resulted in higher frequency waves. Both simulated and experimental waveforms showed similar trends in signal amplitude and frequency when set-up variables were altered.
This study revealed factors that affect the amplitude and frequency of radiation-induced acoustic waves and their relation to the deposited dose characteristics. The agreement between simulated and experimental waveforms verifies the simulation workflow's ability to model such acoustic waves, and indicates that it could be utilized to explore more complex irradiation scenarios and potentially aid in the development of experimental detection systems for in vivo dosimetry.
This work was supported by NSERC and CIHR grants. S.H. acknowledges support by the NSERC CREATE Medical Physics Research Training Network grant 432290.