Ultrasound-Guided Navigation in Robot-Assisted Laparoscopic Radical Prostatectomy

The preservation of the neurovascular bundle (NVB) including cavernous nerves during radical prostatectomy improves the postoperative recovery of sexual potency. At present, the location of NVB is determined by the surgeon's visual estimation. However, NVB is difficult to visualize with simple visual magnification of the surgical field with surgical loupes or laparoscopic lenses due to the periprostatic connective tissue and intraoperative hemorrhage. One approach to better estimate the location of the NVB is to identify a macroscopic landmark to more clearly direct the surgeon to the location of the NVB. The accompanying arteries and veins in the NVB, which are visible with Doppler ultrasound, can serve as a macroscopic landmark to localize the microscopic cavernous nerves in the NVB. Therefore, the use of TRUS imaging during radical prostatectomy can potentially improve the visualization of the NVB and subsequently improve postoperative recovery of potency in men. In addition, the 3-D shape of the prostate gland can potentially be clearly and accurately delineated in ultrasounds imaging, providing direct guidance of landmarks to the surgeon. Recently, intraoperative TRUS imaging has been used to visualize the prostate gland and NVB during laparoscopic radical prostatectomy (LRP). The investigators reported that the intraoperative use of TRUS was helpful in imaging the location and local extent of hypoechoic area(s), providing real-time guidance for the surgeon during NVB release and apical dissection of the prostate, and monitoring a calibrated, lobe-specific, wider dissection around a cancer nodule with suspected extracapsular extension (ECE). With the enhanced visualization of the surgical field by TRUS imaging, they reported significant improvement in NVB preservation and a decreasing rate of positive surgical margin, which is a surrogate for the technical quality of the surgery. However, several aspects related most likely to technology limitations can further be improved. For example, the TRUS probe was manipulated by a human assistant during LRP, compromising image stability especially with Doppler imaging, discarding the pose of the images, and performing navigation based on the recommendations of the assistant rather than using an actual navigation software. Moreover, their application of TRUS can be used in the non-robotic LRP only, because the daVinci® robot used in RALP occupies the place of a human assistant at the end of the operative table. Finally, there was no objective measure to quantify the performance of the navigational aid. Regardless of the study's shortcomings, the authors reported that their positive surgical margin rates decreased precipitously since their use of the TRUS guidance, demonstrating potential benefit of the TRUS-based guidance during surgery. Since their study, the use of intraoperative TRUS guidance during prostate surgery has not gained wide acceptance, and was, in fact, criticized because it requires an additional personnel with an expertise in TRUS. Alternatively, we propose to use the TRUS Robot, a robotic arm to hold and manipulate the TRUS probe remotely, allowing the surgeon to manipulate the TRUS probe without the need for a human assistant during RALP. We also propose to use 3-D TRUS navigation with the images obtained by the TRUS.