Purpose: Radiation dosimetry is a crucial process in radiation therapy to ensure that the correct dose is accurately delivered to the desired location. Despite wide use in clinical intervention, the delivered radiation dose can only be planned and verified via simulation with phantoms, while in vivo and in-line verification of the delivered dose is still absent in the clinic making precision radiotherapy challenging. We have proposed a new imaging modality called X-ray-induced Acoustic Computed tomography (XACT) for in vivo dosimetry during radiotherapy. Specifically, we are developing model-based image reconstruction algorithm for XACT XACT imaging using transperineal ultrasound matrix array.
Methods: Model-based reconstruction algorithm was employed to address the limited-view problem in transperineal sensor geometry. The algorithm builds up an exact X-ray acoustic propagation model in time domains to predict the signal. The reconstruction is performed by minimizing the least square error between the measured signals and predicted signals. The model-based reconstruction results are evaluated by comparing against the ground-truth images.
Results: Model-based reconstruction achieves more satisfactory results than back-projection algorithm with less streak-type artifacts and more low-frequency information. The time-reversal reconstruction has similar performance as model-based reconstruction qualitatively. However, quantitively, the voxel value has larger difference between time-reversal reconstruction and the ground-truth images while the model-based reconstruction has more similar voxel values. The model-based reconstruction algorithm is less time-consuming than the time-reversal algorithm when reconstructing small objects. For large objects, the acoustic model needs to be calculated during each iteration due to memory issues, making it more time-consuming than the time-reversal reconstruction.
Conclusion: Model-based reconstruction algorithm is effective in the reconstruction of transperineal XACT imaging, which can be valuable in prostate radiation therapy. The study also demonstrated the potential of using transperineal XACT imaging as an in-vivo dosimetry tool for radiation beam localization during the prostate treatment.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the National Institute of Health (R37CA240806), American Cancer Society (133697RSG1911001CCE).