MO‐FF‐A1‐04: An Innovative Needle Tip Detection Method for TRUS‐Guided Prostate HDR Brachytherapy

Purpose: In the TRUS‐guided prostate HDR brachytherapy, the needle tip defines the distal end of possible dwells. Needle tip detection plays a critical role in the distance accuracy of dwell positions and hence has a significant impact on dosimetry. However, directly finding the needle tip on the ultrasound images is nothing but an uncertain art. Therefore, the current study was conducted to design and evaluate a novel method to turn this uncertain art into an accurate measurement‐based detection. Method and Materials: Our method used real‐time‐measured residual needle length and offline‐established coordinates to calculate the needle tip position on the TRUS images. Coordinates were established and populated to a lookup table through measurements at possible template‐to‐probe configurations. With the known full length of a needle, the tip position can be calculated using an online‐measured residual length and this lookup table. To evaluate our method, we conducted an experiment in water. The needle tip positions were detected by (1) x‐ray radiographs which we use as the gold‐standards; (2) our measurement‐based method; and (3) direct detection on ultrasound images. 5 different template‐to‐probe configurations were tested, and at each configuration the equipments were assembled for 3 times to assess the assembling reproducibility. Results: With the 5 tested configurations, the reproducibility was found based on the gold‐standard radiographs to be within 0.2 mm. Relative errors using our method and the direct detection method were from 0.6 to 0.8 mm and from 0.9 to 2.3 mm, respectively. Conclusion: A simple and effective method to accurately detect the needle tip on the TRUS images for HDR prostate brachytherapy was developed based on physical‐measurement‐defined coordinate systems. The validity and accuracy of the method was tested and established. The easy‐to‐implement method is clinical‐ready.