Purpose: To demonstrate a method for image reconstruction of linac single-pulse X-ray acoustic computed tomography (XACT). Radiotherapy aims to deliver highly conformal dose to the target volume. Some main limitations are the uncertainty of internal organ motion and knowledge of real-time dose distribution within the patient. Currently there is no standardized method for performing in-vivo dosimetry. XACT is an emerging technology that offers radiation measurement based on the intensity of emitted acoustic waves.
Methods: XACT signals were acquired with immersion-type transducers from two different medium: water and oil. The linac 10MV-FFF photon beam was delivered at a fixed distance from the transducers, using the maximum dose rate available. The 4 μs linac pulse was used to trigger signal acquisition. The XACT signals passed through two amplification stages, then collected in an oscilloscope. Collimator angle rotation allowed tomographic acquisition. MATLAB was used for background subtraction, postfiltering and image reconstruction using simple backprojection technique. 2D field images were obtained for both mediums, and signal noise ratios (SNR) and image intensity profiles were compared. The linear responses as a function of depths were collected. The experiments were performed for single-pulse acquisition and high averaging mode.
Results: The medium’s Grüneisen parameter influences SNR, with photoacoustic peaks being more prominent in oil. Both mediums present sensitivity at lower frequency spectrum (< 50 kHz). The single-pulse XACT reconstruction from oil showed a sharper fall-off in the intensity profile compared to water. The relative intensity obtained as a function of depth showed a linear-trend for single-pulse XACT.
Conclusion: The acquisition of single-pulse XACT and the knowledge of the dose per pulse opens the possibilities for real-time tumor dosimetry. This work demonstrates that single-pulse XACT can be performed with proper instrumentation. In the future, the development of high-resolution transducer arrays could become an alternative for clinical in-tumor dosimetry.
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), Center for Advancement of Science and Technology (OCAST HR19-131).
Not Applicable / None Entered.
TH- External Beam- Photons: portal dosimetry, in-vivo dosimetry and dose reconstruction