Towards an image-guided navigation system for rectal cancer surgery

The standard treatment for rectal cancer is surgical resection of the entire rectum with its surrounding fat. Despite this radical procedure, local recurrence may still occur in up to 10% of patients and is often due to incomplete resection of the tumor area. To better assess tumor borders, image-guided navigation (IGN) can be used. A common form of IGN is where the surgeon uses tracked surgical tools that are visualized on a screen in real-time, relative to a 3D anatomical model created from preoperative imaging. To maintain sufficient navigation accuracy, when operating on the non-rigid rectum, the 3D model should be updated upon tumor motion. It was investigated if including real-time tumor tracking, using electromagnetic (EM) trackers placed close or inside the tumor, can facilitate this. Using an IGN system with wired EM tumor tracking, surgeons assessed proximal rectal tumor borders with a low median error of 3mm. Tumor tracker placement and linking it to the 3D model, however, took 30 minutes of intraoperative time. With implantable wireless trackers these steps can be done preoperatively. It was investigated if a commercially available system for wireless EM tumor tracking in radiotherapy (WL-EMTS) can also be used for IGN surgery. An IGN system was developed using the WL-EMTS for tumor tracking and an optical tracking system for tool tracking. With this IGN system it was possible to reduce incomplete resections of non-palpable breast phantom tumors by a factor of 3, compared to a clinically used wireless localization technique. The IGN system was upgraded using only the WL-EMTS for tumor ánd tool tracking. Accurate navigated resections were possible on virtual lesions in ex vivo liver specimens, where surgeons cut with 0.1±2.3mm accuracy along a planned resection margin. Ideally, the 3D model is projected onto the actual anatomy, such that the navigation screen can be omitted, improving usability. In laparoscopic surgeries this requires laparoscope camera calibration. With oblique-viewing laparoscopes, often used in rectal surgery, camera calibration parameters change when rotating their telescope. Therefore, a camera model was developed modeling these changes, resulting in reprojection accuracies of about 4 pixels (0.4mm) independent on telescope rotation

Accuracy assessment of wireless transponder tracking in the operating room environment

Purpose: To evaluate the applicability of the Calypso® wireless transponder tracking system (Varian Medical Systems Inc., USA) for real-time tumor motion tracking during surgical procedures on tumors in non-rigid target areas. An accuracy assessment was performed for an extended electromagnetic field of view (FoV) of 27.5 × 27.5 × 22.5 cm (which included the standard FoV of 14 × 14 × 19 cm) in which 5DOF wireless Beacon® transponders can be tracked. Methods: Using a custom-made measurement setup, we assessed single transponder relative accuracy, absolute accuracy and jitter throughout the extended FoV at 1440 locations interspaced with 2.5 cm in each orthogonal direction. The NDI Polaris Spectra optical tracking system (OTS) was used as a reference. Measurements were taken in a room without surrounding distorting factors and repeated in an operating room (OR). In the OR, the influence of a carbon fiber and regular stainless steel OR tabletop was investigated. Results: The calibration of the OTS and transponder system resulted in an average root-mean-square error (RMSE) vector of 0.03 cm. For both the standard and extended FoV, all accuracy measures were dependent on transponder to tracking array (TA) distances and the absolute accuracy was also dependent on TA to OR tabletop distances. This latter influence was reproducible, and after calibrating this, the residual error was below 0.1 cm RMSE within the entire standard FoV. Within the extended FoV, this residual RMSE did not exceed 0.1 cm for transponder to TA distances up to 25 cm. Conclusion: This study shows that transponder tracking is promising for accurate tumor tracking in the operating room. This applies when using the standard FoV, but also when using the extended FoV up to 25 cm above the TA, substantially increasing flexibility

Accuracy assessment of target tracking using two 5-degrees-of-freedom wireless transponders

Purpose: Surgical navigation systems are generally only applied for targets in rigid areas. For non-rigid areas, real-time tumor tracking can be included to compensate for anatomical changes. The only clinically cleared system using a wireless electromagnetic tracking technique is the Calypso® System (Varian Medical Systems Inc., USA), designed for radiotherapy. It is limited to tracking maximally three wireless 5-degrees-of-freedom (DOF) transponders, all used for tumor tracking. For surgical navigation, a surgical tool has to be tracked as well. In this study, we evaluated whether accurate 6DOF tumor tracking is possible using only two 5DOF transponders, leaving one transponder to track a tool. Methods: Two methods were defined to derive 6DOF information out of two 5DOF transponders. The first method uses the vector information of both transponders (TTV), and the second method combines the vector information of one transponder with the distance vector between the transponders (OTV). The accuracy of tracking a rotating object was assessed for each method mimicking clinically relevant and worst-case configurations. Accuracy was compared to using all three transponders to derive 6DOF (Default method). An optical tracking system was used as a reference for accuracy. Results: The TTV method performed best and was as accurate as the Default method for almost all transponder configurations (median errors < 0.5°, 95% confidence interval < 3°). Only when the angle between the transponders was less than 2°, the TTV method was inaccurate and the OTV method may be preferred. The accuracy of both methods was independent of the angle of rotation, and only the OTV method was sensitive to the plane of rotation. Conclusion: These results indicate that accurate 6DOF tumor tracking is possible using only two 5DOF transponders. This encourages further development of a wireless EM surgical navigation approach using a readily available clinical system

Real-Time Wireless Tumor Tracking in Navigated Liver Resections: An Ex Vivo Feasibility Study

Background: Surgical navigation systems generally require intraoperative steps, such as intraoperative imaging and registration, to link the system to the patient anatomy. Because this hampers surgical workflow, we developed a plug-and-play wireless navigation system that does not require any intraoperative steps. In this ex vivo study on human hepatectomy specimens, the feasibility was assessed of using this navigation system to accurately resect a planned volume with small margins to the lesion. Methods: For ten hepatectomy specimens, a planning CT was acquired in which a virtual spherical lesion with 5 mm margin was delineated, inside the healthy parenchyma. Using two implanted trackers, the real-time position of this planned resection volume was visualized on a screen, relative to the used tracked pointer. Experienced liver surgeons were asked to accurately resect the nonpalpable planned volume, fully relying on the navigation screen. Resected and planned volumes were compared using CT. Results: The surgeons resected the planned volume while cutting along its border with a mean accuracy of − 0.1 ± 2.4 mm and resected 98 ± 12% of the planned volume. Nine out of ten resections were radical and one case showed a cut of 0.8 mm into the lesion. The sessions took approximately 10 min each, and no considerable technical issues were encountered. Conclusions: This ex vivo liver study showed that it is feasible to accurately resect virtual hepatic lesions with small planned margins using our novel navigation system, which is promising for clinical applications where nonpalpable hepatic metastases have to be resected with small resection margins

Real-time wireless tumor tracking during breast conserving surgery

Purpose To evaluate a novel surgical navigation system for breast conserving surgery (BCS), based on real-time tumor tracking using the Calypso®4D Localization System (Varian Medical Systems Inc., USA). Navigation-guided breast conserving surgery (Nav-BCS) was compared to conventional iodine seed-guided BCS (125I-BCS).MethodsTwo breast phantom types were produced, containing spherical and complex tumors in which wireless transponders (Nav-BCS) or a iodine seed (125I-BCS) were implanted. For navigation, orthogonal views and 3D volume renders of a CT of the phantom were shown, including a tumor segmentation and a predetermined resection margin. In the same views, a surgical pointer was tracked and visualized. 125I-BCS was performed according to standard protocol. Five surgical breast oncologists first performed a practice session with Nav-BCS, followed by two Nav-BCS and 125I-BCS sessions on spherical and complex tumors. Postoperative CT images of all resection specimens were registered to the preoperative CT. Main outcome measures were the minimum resection margin (in mm) and the excision times.ResultsThe rate of incomplete tumor resections was 6.7% for Nav-BCS and 20% for 125I-BCS. The minimum resection margins on the spherical tumors were 3.0 ± 1.4 mm for Nav-BCS and 2.5 ± 1.6 mm for 125I-BCS (p = 0.63). For the complex tumors, these were 2.2 ± 1.1 mm (Nav-BCS) and 0.9 ± 2.4 mm (125I-BCS) (p = 0.32). Mean excision times on spherical and complex tumors were 9.5 ± 2.7 min and 9.4 ± 2.6 min (Nav-BCS), compared to 5.8 ± 2.2 min and 4.7 ± 3.4 min (125I-BCS, both (p < 0.05).ConclusionsThe presented surgical navigation system improved the intra-operative awareness about tumor position and orientation, with the potential to improve surgical outcomes for non-palpable breast tumors. Results are positive, and participating surgeons were enthusiastic, but extended surgical experience on real breast tissue is required

Accurate surgical navigation with real-time tumor tracking in cancer surgery

In the past decades, image-guided surgery has evolved rapidly. In procedures with a relatively fixed target area, like neurosurgery and orthopedics, this has led to improved patient outcomes. In cancer surgery, intraoperative guidance could be of great benefit to secure radical resection margins since residual disease is associated with local recurrence and poor survival. However, most tumor lesions are mobile with a constantly changing position. Here, we present an innovative technique for real-time tumor tracking in cancer surgery. In this study, we evaluated the feasibility of real-time tumor tracking during rectal cancer surgery. The application of real-time tumor tracking using an intraoperative navigation system is feasible and safe with a high median target registration accuracy of 3 mm. This technique allows oncological surgeons to obtain real-time accurate information on tumor location, as well as critical anatomical information. This study demonstrates that real-time tumor tracking is feasible and could potentially decrease positive resection margins and improve patient outcome