Convex Endobronchial Ultrasound-Guided Fiducial Placement for Malignant Central Lung Lesions: A Case Series

Characterization of Markerless Tumor Tracking Using the On-Board Imager of a Commercial Linear Accelerator Equipped With Fast-kV Switching Dual-Energy Imaging

PURPOSE

To describe and characterize fast-kV switching, dual-energy (DE) imaging implemented within the on-board imager of a commercial linear accelerator for markerless tumor tracking (MTT).

METHODS AND MATERIALS

Fast-kV switching, DE imaging provides for rapid switching between programmed tube voltages (ie, 60 and 120 kVp) from one image frame to the next. To characterize this system, the weighting factor used for logarithmic subtraction and signal difference-to-noise ratio were analyzed as a function of time and frame rate. MTT was evaluated using a thorax motion phantom and fast kV, DE imaging was compared versus single energy (SE) imaging over 360 degrees of rotation. A template-based matching algorithm was used to track target motion on both DE and SE sequences. Receiver operating characteristics were used to compare tracking results for both modalities.

RESULTS

The weighting factor was inversely related to frame rate and stable over time. After applying the frame rate-dependent weighting factor, the signal difference-to-noise ratio was consistent across all frame rates considered for simulated tumors ranging from 5 to 25 mm in diameter. An analysis of receiver operating characteristics curves showed improved tracking with DE versus SE imaging. The area under the curve for the 10-mm target ranged from 0.821 to 0.858 for SE imaging versus 0.968 to 0.974 for DE imaging. Moreover, the residual tracking errors for the same target size ranged from 2.02 to 2.18 mm versus 0.79 to 1.07 mm for SE and DE imaging, respectively.

CONCLUSIONS

Fast-kV switching, DE imaging was implemented on the on-board imager of a commercial linear accelerator. DE imaging resulted in improved MTT accuracy over SE imaging. Such an approach may have application for MTT of patients with lung cancer receiving stereotactic body radiation therapy, particularly for small tumors where MTT with SE imaging may fail.

Peripheral Lung Nodule Diagnosis and Fiducial Marker Placement Using a Novel Tip-Tracked Electromagnetic Navigation Bronchoscopy System

BACKGROUND

Electromagnetic navigation (EMN) has improved bronchoscopic access to peripheral pulmonary nodules. A novel EMN system utilizing novel tip-tracked instruments for endobronchial [electromagnetic navigation bronchoscopy (ENB)] as well as transthoracic lung biopsy [electromagnetic-guided transthoracic needle aspiration (EMTTNA)] has become available. The system provides real-time feedback as well as the ability to biopsy lesions outside of the airway. These advances have the potential to improve diagnostic yield over previous EMN systems.

METHODS

We performed a retrospective review of consecutive peripheral bronchoscopy cases utilizing a novel EMN platform for biopsy and/or fiducial marker (FM) placement at a tertiary care university hospital. We analyzed factors that may influence diagnostic yield including lesion size.

RESULTS

Our study included 108 patients who underwent EMN-guided bronchoscopy between June 2015 and April 2017 for the diagnosis of peripheral lung lesions and/or the placement of FMs for stereotactic body radiotherapy. Ninety-three patients underwent biopsy utilizing ENB +/- EMTTNA. The combined diagnostic yield was 78%. EMTTNA provided a diagnosis for 5 patients in whom the ENB biopsy results were negative. Diagnostic yield by nodules <20, 20 to 30, and >30 mm in size was 30/45 (67%), 27/30 (90%), and 16/18 (89%), respectively. Sixty-five patients underwent FM placement with a total of 133 FM placed.

CONCLUSION

This novel tip-tracked EMN system incorporating both ENB and EMTTNA can guide biopsy and FM placement with a high degree of success and with a low complication rate. Multicentered prospective trials are required to develop algorithmic approaches to combine ENB and EMTTNA into a single procedure.

Convex Probe EBUS-guided Fiducial Placement for Malignant Central Lung Lesions

BACKGROUND

Stereotactic body radiotherapy (SBRT) had become a therapeutic modality in patients with primary tumors, locally recurrent as well as oligometastasis involving the lung. Some modalities of SBRT require fiducial marker (FM) for dynamic tumor tracking. Previous studies have focused on evaluating bronchoscopic-guided FM placement for peripheral lung nodules. We describe the safety and feasibility of placing FM using real-time convex probe endobronchial ultrasound (CP-EBUS) for SBRT in patients with centrally located hilar/mediastinal masses or lymph nodes.

METHODS

This is a retrospective review of patients who were referred to Beth Israel Deaconess Medical Center's multidisciplinary thoracic oncology program for FM placement to pursue SBRT.

RESULTS

Thirty-seven patients who underwent real-time CP-EBUS were included. Patients had a median age of 71 years [interquartile range (IQR), 59.5 to 80.5]. The median size of the lesion was 2.2 cm (IQR, 1.4 to 3.3 cm). The median distance from the central airway was 2.4 cm (IQR, 0 to 3.4 cm). A total of 51 FMs (median of 1 per patient) were deployed in 37 patients. At the time of SBRT planning, 46 (90.2%) were confirmed radiologically in 32 patients. Patients with unsuccessful fiducial deployment (n=5) underwent a second procedure using the same technique. Of those, 3 patients had a successful fiducial placement via bronchoscopy, 1 patient required FM placement by percutaneous computed tomography-guided approach and 1 patient required FM placement through EUS by gastroenterology.

CONCLUSION

CP-EBUS-guided FM placement for patients with malignant lymph nodes and central parenchymal lung lesions appears to be safe and feasible.

Fiducial marker placement for stereotactic body radiation therapy via convex probe endobronchial ultrasound: a case series and review of literature

Convex probe endobronchial ultrasound (CP-EBUS) and stereotactic body radiotherapy (SBRT) are valuable tools in the diagnosis, staging, and treatment of thoracic malignancies. With widespread clinical adoption, novel uses of CP-EBUS beyond mediastinal diagnosis and staging continue to be discovered. SBRT is an attractive treatment strategy in early-stage lung cancer and oligo-metastatic disease of the chest when a surgical approach is either not feasible or desirable. Accurate application of SBRT is aided by the placement of radio-opaque fiducial markers (FM) to compensate for respiratory cycle movements. We describe eight patients with central thoracic lesions, either known or suspected to be malignant, who underwent EBUS bronchoscopy with lesion sampling and successful intralesional placement of modified FM via our technique, review the existing literature on this topic, and discuss the nuances of coding and billing aspects of FM placement.