was then repeated to confrm that the ablation zone covered the entire tumor as well as to evaluate for any immediate complications. Follow-up as far as nine months confrmed that the lesion had been successfully treated. Indeed, as will be discussed in the following section, intraoperative CT is a powerful tool that can make the bronchoscopic treatment of peripheral cancers a more common and effective practice in the future.

Limitations oftheLiterature

With any emerging technology in a challenging feld, the medical literature—while informa- tive—will necessarily have some pitfalls and confnes. In the case of cone-beam CT for the peripheral pulmonary lesion, studies have often been retrospective, single-center, and even single operator. This limits the quality and generalizability of the data. Prospective trials have been relatively small.

There is also the issue of heterogeneity between the studies. As was detailed above, different studies utilized different navigational or imaging modalities and different combinations thereof. Different-sized bronchoscopes have been used (which is particularly germane to the issue of reaching peripheral lesions) and different biopsy tools employed. Different defnitions of diagnostic yield have been applied as well and only a few report sensitivity for malignancy. Importantly, data on radiation exposure and the interpretation thereof have been variable. For all of these reasons, comparisons between studies are diffcult.

Last, the effect of experience must be taken into account. Many of the aforementioned studies re ect the somewhat initial experiences of the different centers with this technology. As demonstrated by the recent Verhoeven study described above, further exercise over time can improve one’s skill in the use of a given technology. It can possibly be anticipated that improved outcomes would result from these same investigators as they gained more experience and subsequent studies performed.

Future Directions

The future holds many opportunities for progress in this area of investigation. The research described in this chapter needs to be replicated in larger, well-designed, and prospective studies. Dedicated attention needs to be given to radiation exposure with investigation into how to minimize it in particular. Advancements in software, hardware, and the algorithms that link these together will hopefully lead to better images with less radiation.

Additionally, a new era in pulmonary medicine has been entered with the introduction of robotic bronchoscopy. The versatility in steering and ability for minute changes in any direction provide maneuverability that has not been seen in bronchoscopy before. Initial studies have been promising [65–69]. Combined with the real-time imaging that cone-beam CT provides, along with existing navigational technologies, we may fnally witness diagnostic yield breach the 70% ceiling as was observed in the robotic study by Benn described above. Another study specifcally combining robotic bronchoscopy with intraoperative CT is currently underway with surely more to come [60].

Finally, CBCT may prove to be an ideal platform for bronchoscopic ablation of peripheral tumors. The minimally invasive treatment of peripheral tumors is an area of active research which could solidify bronchoscopy as a “one-­ stop shop” of diagnosis, nodal staging, and treatment of early-stage cancers—all in one setting [34]. Precise localization of tumors for ablation is critical because ablation zones are larger than the lesions within them. As such, nearby structures may be affected and, thus, real-time, three-­ dimensional imaging would be quite helpful. In-room imaging has the added beneft of immediate evaluation for complications as well.

Conclusion

Intraoperative CT imaging is an area of active research in peripheral bronchoscopy but still in its relatively early stages. As technology contin-

ues to innovate and further investigation continues, we will hopefully see continued advancement in our ability to diagnose peripheral lesions— ones that are increasingly diffcult to reach and progressively smaller, enabling us to detect lung cancer at ever earlier junctures. Cone-beam CT is currently at the forefront of this endeavor, having an established place in our armamentarium and holding much promise for the future.

Acknowledgments  We thank Mr. David Aten, MA, CMI for invaluable help with medical illustration.

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