Augmented Fluoroscopy for Guidance of Bronchoscopic Biopsy of Pulmonary Nodules

To the Editor: We read with great interest the paper by Pritchett et al,1 and the accompanying editorial by Casal,2 regarding use of intraprocedural cone-beam computed tomography (CBCT) imaging to accurately target bronchoscopic sampling of parenchymal lesions. With a medial lesion size of 16 mm, and 94% of lesions positioned within the middle or outer two thirds of the lung, the diagnostic yield of 83% and sensitivity for malignancy of 91% is impressive, and warrants further investigation. We particularly note the excellent safety of this technique, with mean effective radiation dose (2 mSv) consistent with diagnostic chest CT imaging, though clearly in excess of radiation exposure following standard planar fluoroscopic guidance of bronchoscopic procedures.3 We note that the authors used augmented fluoroscopic imaging based on CBCT images acquired following patient intubation but before commencement of bronchoscopy. As such we suggest that this study examines the utility of augmented fluoroscopy (or augmented reality as it has also previously been described4), rather than CBCT itself. Augmented reality has previously been associated in percutaneous biopsy with improvements in diagnostic accuracy, procedure time, and radiation dose.5 We are excited to see the first formal description of its use in the field of interventional pulmonology. Dr Casal very insightfully distinguishes, in his editorial, between navigation (as is achieved by augmented fluoroscopy) and confirmation. We have previously utilized CBCT imaging (which we termed CT-fluoroscopic guidance) to confirm cryoprobe positioning during bronchoscopic investigation of interstitial lung disease in order to achieve more accurate targeting of transbronchial cryobiopsy.6 Our preliminary report confirms feasibility of CT-fluoroscopy in confirming with high accuracy the position of the cryoprobe before performance of cryobiopsy, with the potential to both increase diagnostic yield (through more accurate targeting of biopsy to radiologic abnormalities) and reduce complication rates (through safer positioning of probe in relation to pleura/vascular structures). We successfully demonstrated the feasibility and potential of the technique, however, our early experience was complicated by high effective radiation doses. Reductions in radiation exposure were achieved through a contraction of the infero-superior imaging field dimension, as well as imaging time interval and other exposure factors, such that later procedures were associated with effective doses of 9 to 19 mSv, consistent with that reported for other diagnostic interventions.7,8 Use of augmented fluoroscopy based on CBCT imaging, as described by Pritchett et al,1 may be a valuable method to further reduce radiation exposure, without compromise of diagnostic accuracy. Greater detail regarding imaging parameters and radiation exposure should be encouraged in future studies utilizing CBCT for guidance of bronchoscopic interventions. We agree wholeheatedly with Dr Casal that CBCT will likely be invaluable in the developing field of bronchoscopic ablation of peripheral lung tumors, both to establish position of treatment probes before commencement of ablation, as well as for ablation zone monitoring once treatments have been commenced,9,10 and believe more work is required to advance and refine the technique, including establishing whether CBCT for “confirmation” of target via intraprocedural imaging is superior to augmented fluoroscopic “navigation”—with diagnostic sensitivity of 91% the added radiation exposure may not be warranted. We congratulate Pritchett et al for their innovative development to further improve bronchoscopic investigation of peripheral nodules and believe their report will be valuable in informing future studies seeking to refine the technique of CBCT-guidance (or CT-fluoroscopy) of bronchoscopic procedures, especially given (as noted by Dr Casal) CBCT is “here to stay.”2 Daniel P. Steinfort, FRACP, PhD, MB, BS*† Ivan Vrjlic, B.Sc‡ Louis B. Irving, MBBS, FRACP*Departments of *Respiratory Medicine‡Radiology, Royal Melbourne Hospital†Department of Medicine (RMH), University of Melbourne, Parkville, Vic., Australia