Broadband detection of dynamic acoustic emission process induced by 6 MV therapeutic X-ray beam from a clinical linear accelerator

Acoustic waves induced by megavoltage photon beam from a clinical linear accelerator (Linac) could provide location and dosimetric information of actual delivered radiation during the course of therapy. In this study, we investigated, for the first time, the technical feasibility of detecting the dynamic acoustic emission process induced by Linac with high SNR. A 6 MV pulsed X-ray beam produced by a Linac was used to excite the X-ray acoustic signals from the water-gelatin phantom and the carbon-gelatin phantom. The induced acoustic signals were collected with a circular plane piston, immersion hydrophone in the frequency range from 100 kHz to 1 MHz perpendicular to the incident X-ray beam direction. The signals were amplified using a preamplifier with a bandwidth of 50 KHz-5 MHz at 34 dB and sampled by a high-speed 14-Bit 100 MS/s data acquisition card. A trigger circuit was designed to synchronize the process of incident pulsed X-ray generation and emitted acoustic signal acquisition. The dynamic X-ray acoustic emission process was consecutively detected from both phantoms with high SNR. The peak amplitude shows a marked increase in the phase of X-ray irradiation and then a rapid fall-off with different dynamic acoustic signal profiles in water-gelatin phantom, suggesting the different processes of accumulation and the absorption of the X-ray energy in different phantom properties. The acoustic emission process of carbon-gelatin phantom lasted more than 5 ms induced by a single X-ray beam with 5 µs pulse width. X-ray acoustic waves detected with high SNR may be used to verify the dose distribution during radiation therapy. Moreover, it may open the opportunity of using X-ray acoustic signals emitted from the tumor to evaluate the radiation treatment efficacy.