Purpose: Brachytherapy (BT) is a form of radiation therapy, which relies on the insertion of needles to deliver radiation. Accurate needle tip identification is key for safe and effective BT, as errors can result in radiation delivery that deviates from the planned dose. Typically, standard brightness (B)-mode ultrasound (US) imaging is used for needle tip identification; however, artifacts can limit the visibility of needles. We propose a novel wireless mechanical oscillator for needle perturbation in a power Doppler (PD)-based needle tip identification method to overcome these limitations and improve needle tip identification accuracy in BT.
Methods: Our wireless mechanical oscillator is capable of oscillating at a fixed and controllable frequency and amplitude, featuring a cylindrical end-piece designed specifically for use with BT needle mandrins. We evaluated our method using a tissue equivalent phantom with a standard clinical needle implant pattern and an implant pattern designed to maximize needle shadowing. Needle tips were identified with B-mode US alone, with B-mode and PD US together, and with PD US alone by reducing B-mode gain to 0, simulating the clinical case of non-visible needles. Performance was quantified using a tip error metric computed using the clinical standard of ideal reference needles.
Results: Absolute mean ± standard deviation tip error was 0.33±0.27mm (B-mode), 0.39±0.23mm (B-mode+PD), and 0.77±0.89mm (BlindedPD) for the standard clinical needle implant and 0.80±1.70mm (B-mode), 0.34±0.47mm (B-mode+PD), and 0.43±0.62mm (BlindedPD) for the shadowed needle implant.
Conclusion: Our PD US method provided equivalent tip identification accuracy for the standard clinical needle implant and superior accuracy for shadowed needles, including the ability to visualize needles that could not be seen using B-mode US alone due to shadowing. Our wireless oscillator is easy to use and requires no modification to the clinical workflow, providing promise for the clinical utility of our method in BT procedures.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canadian Institutes of Health Research (CIHR), and the Ontario Institute for Cancer Research (OICR). N Orlando was supported in part by the Queen Elizabeth II Graduate Scholarship in Science and Technology.