Purpose: High-dose-rate brachytherapy (HDR-BT) for prostate cancer relies on accurate needle tip identification to ensure patient safety and delivery of the prescribed radiation dose. Image artifacts can make it difficult to visualize the needle tip accurately using standard 2D brightness (B)-mode ultrasound (US) guidance. The purpose of this study is to develop and validate, in phantom, a power Doppler (pD) US-based tip identification method, which we hypothesize will overcome these limitations and improve intraoperative needle tip visualization.
Methods: An experiment was completed in a tissue-mimicking agar phantom following a standard clinical HDR-BT procedure. 13 unobstructed and 10 shadowed needles were imaged. For each needle, the tip location was selected by two observers, first using B-mode US and then using pD US while the needle was vibrated by a custom-made mechanical oscillator. Tip identification accuracy was quantified as mean insertion depth error (IDE), which is the difference between tip position obtained from B-mode/pD US and the gold standard tip position, determined using end length measurements.
Results: Mean IDE Â± standard deviation, averaged for two observers, was 1.2Â±0.9mm (B-mode US) and 0.3Â±1.0mm (pD US) for unobstructed needles, and 1.1Â±1.6mm (B-mode US) and -0.1Â±1.7mm (pD US) for shadowed needles. A two-way ANOVA showed a statistically significant reduction in IDE with the pD US method compared to B-mode US (p<.0001). Observer and needle distance from the US probe had no statistically significant effect on IDE, and no correlation was found between IDE and needle insertion depth, demonstrating the robustness of our method.
Conclusion: A pD US tip identification method requiring minimal modifications to the clinical workflow was developed and implemented in an HDR-BT phantom experiment, demonstrating improved needle tip visualization. Future work will focus on translating this method to clinical HDR-BT procedures, where it has the potential to improve patient safety and treatment effectiveness.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the Ontario Institute for Cancer Research (OICR), the Natural Sciences and Engineering Research Council of Canada (NSERC), and the Canadian Institutes of Health Research (CIHR).