Tipping Point: Cone Beam CT With Augmented Fluoroscopy for the Biopsy and Treatment of Peripheral Nodules

In Reply:

It is with great enthusiasm and appreciation that we read the Letter to the Editor by Steinfort et al¹ as well as the editorial by Casal² regarding our recent manuscript detailing our experience utilizing cone beam computed tomography (CBCT) with augmented fluoroscopy (AF) during navigated bronchoscopy.³ We are also excited to read about the experience of using CBCT to ensure accurate and safe probe positioning for bronchoscopic cryobiopsy.

Our aim was to develop a technique capable of achieving high diagnostic yield while maintaining an excellent safety profile. In particular, we found that the use of AF provided us with an effective way to reduce the number of additional CBCT scans for confirmation purposes by visualizing catheter positioning with respect to the projected tumor location in multiple fluoroscopic planes. In fact, only a single CBCT scan was performed in the majority of cases reported in our study. The use of intraprocedural CBCT is nevertheless a critical component for the accuracy of the AF technique. Reliance on preprocedural computed tomography (CT) (as is the case with electromagnetic navigation bronchoscopy) has been shown to have inherent CT-to-body divergence (up to 35.9 mm) compared with intraprocedural CBCT.⁴ In addition, CBCT units provide a fully calibrated environment where CBCT and fluoroscopic images are automatically fused and overlaid, making the technique less prone to registration error.

The use of “tool-in-lesion” CBCT confirmation may still be necessary for centers where rapid onsite pathologic examination is not available. In our study, we rarely needed such confirmational CBCT scans; however, in cases where a diagnosis was elusive, the confirmation scan was helpful to ensure that the biopsy tool was indeed in the lesion and this may in part be responsible for our high sensitivity for malignancy (91.3%) as well as the relatively high negative predictive value (79.3%) of the procedure. We completely agree that for the purposes of peripheral navigation, the star of the show in our experience has been the use of AF. This has given us confidence to routinely attempt biopsy of lesions as small as 7 mm while maintaining high diagnostic yield (84.2% in lesions ≤10 mm).³

Because of the use of low-dose CBCT imaging protocols, we achieved radiation dose levels comparable to CBCT-guided transthoracic needle interventions and considerably lower than conventional CT guidance.⁵ It should be noted that CBCT dose levels are manufacturer-specific so our results cannot be generalized. Active vertical collimation is good practice and is now commonly applied to all of our intraprocedural CBCT scans. In the near future, we can expect that alternative scanning protocols, that is using reduced frame rate, will be available to enable the next steps in radiation dose reduction.

AF, not to be confused with the augmented reality (AR) navigation technology, integrates intraprocedural CBCT data with live fluoroscopy. AR navigation, as used in Racadio et al,⁶ uses high-resolution optical cameras integrated into the detector housing of the x-ray system to construct a unique view of the patient’s anatomy in relation to the incision sites in the skin. The aid of AR navigation technology could, however, be a valuable method to reduce radiation dose exposure in transthoracic needle punctures, just as it has done with minimally invasive spine surgery. Accounting for the lack of clinical experience to date for AR beyond spine surgery, both AF and AR navigation are based on CBCT imaging and will be available for the same CBCT units, thus potentially enabling a smooth combination of bronchoscopic and transthoracic approaches in a single session in the hybrid operating room.⁷

As stressed in Dr Casal’s editorial, CBCT imaging will be a must-have for anyone considering the application of bronchoscopic transbronchial tumor ablation. Thus far, no virtual or 2D technology has proven to be accurate enough to confidently apply ablative energy in the lung, making CBCT an integral component of this new procedure. Early publications on bronchoscopic thermal ablation position CBCT imaging as mandatory for both accurate catheter positioning and immediate assessment of procedure effectiveness⁸ thereby supporting instant decision making on treatment continuation and adequate follow-up. As such, CBCT has become a compulsory and fundamental part of an ongoing multicenter trial of endobronchial microwave ablation.

We fully acknowledge that the results of this retrospective, single-center study may not be generalizable. Nevertheless, they do suggest modularity of CBCT imaging during bronchoscopic biopsy procedures used for navigation and confirmation, with or without the combination of complementary navigation systems. A recent preclinical feasibility study using prototype software (Philips) showed that navigation toward peripheral targets in the lung is even feasible using CBCT guidance alone.⁹ Upcoming clinical trials studying the impact upon outcome, workflow, and costs should show the potential role of CBCT-guided navigation in the clinical practice of advanced diagnostic bronchoscopy, interventional pulmonology, and thoracic surgery.

This work is just the beginning of our journey into redefining the cancer patient’s diagnosis and treatment pathway with the ultimate goal of being able to diagnose, stage, and treat in a single procedure. We are therefore thankful to the authors of the Editorial² and Letter to the Editor¹ for their recognition of our work and their own contribution in building positive momentum around the topic.

Michael A. Pritchett, DO, MPH*

Stéphanie Schampaert, PhD†
*FirstHealth of the Carolinas and Pinehurst Medical Clinic, Pinehurst, NC
†Philips, Best, The Netherlands