After breast-conserving surgery, positive margins occur when breast cancer cells are found on the resection margin, leading to a higher chance of recurrence and the need for repeat surgery. The NaviKnife is an electromagnetic tracking-based surgical navigation system that helps to provide visual and spatial feedback to the surgeon. In this study, we conduct a gross evaluation of this navigation system with respect to resection margins. The trajectory of the surgical cautery relative to ultrasound-visible tumor will be visualized, and its distance and location from the tumor will be compared with pathology reports. Six breast-conserving surgery cases that resulted in positive margins were performed using the NaviKnife system. Trackers were placed on the surgical tools and their positions in three-dimensional space were recorded throughout the procedure. The closest distance between the cautery and the tumor throughout the procedure was measured. The trajectory of the cautery when it came closest to the tumor model was plotted in 3D Slicer and compared with pathology reports. In two of the six cases, the side at which the cautery came the closest to the tumor model coincided with the side at which positive margins were found from pathology reports. Our method shows that positive margins occur mainly in areas that are not visible from ultrasound imaging. Our system will need to be used in combination with intraoperative tissue characterization methods to effectively predict the occurrence and location of positive margins.
Up to 35% of breast-conserving surgeries fail to resect all the tumors completely. Ideally, machine learning methods using the iKnife data, which uses Rapid Evaporative Ionization Mass Spectrometry (REIMS), can be utilized to predict tissue type in real-time during surgery, resulting in better tumor resections. As REIMS data is heterogeneous and weakly labeled, and datasets are often small, model performance and reliability can be adversely affected. Self-supervised training and uncertainty estimation of the prediction can be used to mitigate these challenges by learning the signatures of input data without their label as well as including predictive confidence in output reporting. We first design an autoencoder model using a reconstruction pretext task as a self-supervised pretraining step without considering tissue type. Next, we construct our uncertainty-aware classifier using the encoder part of the model with Masksembles layers to estimate the uncertainty associated with its predictions. The pretext task was trained on 190 burns collected from 34 patients from Basal Cell Carcinoma iKnife data. The model was further trained on breast cancer data comprising of 200 burns collected from 15 patients. Our proposed model shows improvement in sensitivity and uncertainty metrics of 10% and 15.7% over the baseline, respectively. The proposed strategies lead to improvements in uncertainty calibration and overall performance, toward reducing the likelihood of incomplete resection, supporting removal of minimal non-neoplastic tissue, and improved model reliability during surgery. Future work will focus on further testing the model on intraoperative data and additional exvivo data following collection of more breast samples.
PURPOSE: Lumpectomy is the resection of a tumor in the breast while retaining as much healthy tissue as possible. Navigated lumpectomy seeks to improve on the traditional technique by employing computer guidance to achieve the complete excision of the cancer with optimal retention of healthy tissue. Setting up navigation in the OR relies on the manual interactions of a trained technician to align three-dimensional virtual views to the patient’s physical position and maintain their alignment throughout surgery. This work develops automatic alignment tools to improve the operability of navigation software for lumpectomies. METHODS: Preset view buttons were developed to refine view setup to a single interaction. These buttons were tested by measuring the reduction in setup time and the number of manual interactions avoided through their use. An auto-center feature was created to ensure that three-dimensional models of anatomy and instruments were in the center of view throughout surgery. Recorded data from 32 lumpectomy cases were replayed and the number of auto-center view shifts was counted from the first cautery incision until the completion of the excision of cancerous tissue. RESULTS: View setup can now be performed in a single interaction compared to an average of 13 interactions (taking 83 seconds) when performed manually. The auto-center feature was activated an average of 33 times in the cases studied (n=32). CONCLUSION: The auto-center feature enhances the operability of the surgical navigation system, reducing the number of manual interactions required by a technician during the surgery. This feature along with preset camera view options are instrumental in the shift towards a completely surgeon-operable navigated lumpectomy system.
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