Abstract
Background:
Studies have shown the potential of electromagnetic navigation bronchoscopy (ENB)-guided transbronchial microwave ablation (MWA) for treating pulmonary nodules. The role of cone-beam computed tomography (CBCT) in the procedure remains unknown.
Objectives:
To investigate the efficacy and safety of employing CBCT during ENB-guided transbronchial MWA for pulmonary nodules.
Design:
Retrospective analysis of clinical records.
Methods:
Patients who underwent ENB-guided transbronchial MWA at the Department of Thoracic Surgery, Tongji Hospital. Patients were categorized into two groups: those who received CBCT during the procedure and those who did not. Technical and ablation success rates, complication rates, and patient characteristics were assessed.
Results:
A total of 283 patients with 371 nodules were included in the final analysis. The technical success rate was significantly higher in the CBCT group (97.0%) compared to the non-CBCT group (91.5%, p = 0.034). The overall ablation success rate was 88.1%, with the CBCT group demonstrating a higher rate (90.9% vs 81.5%, p = 0.018). Complication rates were similar between the two groups, with no significant differences.
Conclusion:
The use of CBCT in ENB-guided transbronchial MWA significantly increases the technical and ablation success rates without raising complication rates. These findings underscore the potential advantages of CBCT in enhancing procedural outcomes for patients with pulmonary nodules. Further validation through larger, multi-center studies with longer follow-up is warranted.
Keywords
Introduction
Lung cancer is the most common cancer and the leading cause of cancer-related death mortality globally, with over 800,000 new cases and 700,000 deaths reported in China in 2022.1,2 With the improvement of health awareness and the popularization of low-dose computed tomography (CT) screening, pulmonary nodules, defined as <3 cm lesions surrounded by lung tissue detected by CT with possible malignancy, are now more frequently identified. Video-assisted thoracoscopic surgery (VATS) is the preferred method for resectable early-staged lung cancer with confirmed prolongation of survival.3 –5 However, for patients with multiple pulmonary nodules, enlarged pulmonary nodules or metachronous second primary pulmonary nodules after previous lung surgery, surgery might not be applicable, underscoring the need for a less invasive approach.6 –8
Microwave ablation (MVA) works by increasing the local temperature of the target lesion, leading to protein denaturation and tissue necrosis locally. 9 Advances in electromagnetic navigation bronchoscopy (ENB) techniques have made transbronchial ablation feasible. Compared to percutaneous ablation, transbronchial ablation carries a lower risk of complications, such as pneumothorax, bleeding, and bronchopleural fistula since the pleura remains intact. 10 ENB uses electromagnetic signals to track the position of the navigation catheter in real time. 11 However, electromagnetic signals can be affected by various factors, reducing ENB precision.
To enhance the precision of ENB, cone-beam CT (CBCT) can be used to verify the position of the navigation catheter and the target lesion. Moreover, CBCT can be deployed in hybrid operating rooms to provide real-time imaging guidance. Studies have shown that CBCT may improve the diagnostic yield of ENB-guided biopsy of pulmonary nodules.12,13 Unlike biopsy, however, ablation requires slightly less precision, as it creates a larger treatment zone to cover target lesions. Whether CBCT is necessary in this context remains unclear, particularly given the potential downsides, such as prolonged procedure times and increased radiation exposure. Evidence on the benefits and risks of using CBCT in ENB-guided ablation is still limited. Therefore, we conducted this study to evaluate the efficacy and safety of CBCT-assisted ENB-guided transbronchial MWA for pulmonary nodules.
Methods
Study design
The study flowchart is shown in Figure 1. Patient data including demographics, medical history, nodule characteristics, and ENB-guided MWA specifics were collected from electronic medical records. Then, records were screened according to inclusion and exclusion criteria. The included patients who underwent ENB-guided MWA procedures were divided into a CBCT group and a non-CBCT group according to whether CBCT was employed. The employment of CBCT depends on whether CBCT has been introduced into our clinical center. Once CBCT is introduced, its employment is incorporated into the routine procedure. Patient and nodule characteristics were analyzed. During the procedure, technical success would be evaluated by the operator, which was defined as the successful placement of the ablation catheter to the target lesion confirmed by CBCT or radial endobronchial ultrasound (r-EBUS) probe. Only technical successful cases would receive ablation. Otherwise, the procedure would be terminated. Chest CT was performed on the first day, 1 month, 6 months post-ablation, and more in the future (if possible) to evaluate the ablation success and complications of ENB-guided MWA. Ablation success was defined as the complete distortion in the shape of the original nodule and continuous reduction in the size of the ablation lesion in CT images for at least 6 months, which requires CT surveillance during follow-up.14,15 Patients were interviewed about subjective discomforts through telephone. The follow-up period ended in September 2024. The reporting of this study conforms to the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement. 16 The checklist from the relevant guideline can be acquired in the Supplemental File.

The study flow chart of the study. Records of patients who received ENB-guided transbronchial MWA for treating pulmonary nodules were retrieved from the EMR system. A total of 476 records were retrieved. After screening, 58 records were excluded due to incomplete data, 29 due to no specific records of the employment of CBCT, 81 due to loss or lack of follow-up, and 7 due to decline of participation, resulting in 301 patients and 389 nodules included in the study. Patients were divided into two groups according to the employment of CBCT, resulting in 83 patients and 118 nodules in the CBCT unemployed group, and 218 patients and 271 nodules in the CBCT employed group. Among them, 10 patients with 10 nodules and 8 patients with 8 nodules met technical failure. The remaining 73 patients and 108 nodules, and 210 patients, and 263 nodules received ablation and were further analyzed.
Patient selection
Between October 2018 and May 2024, patients who underwent ENB-guided transbronchial MWA for pulmonary nodules at the Department of Thoracic Surgery, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, were included. The inclusion criteria were as follows: (a) pulmonary nodules were confirmed by chest CT; (b) pulmonary nodules were confirmed of or with a high possibility of malignancy; and (c) patients with multiple pulmonary nodules, enlarged pulmonary nodules or metachronous second primary pulmonary nodules after previous lung surgery, or resectable lung cancer but poor cardiopulmonary function who are not able to tolerate surgery. The exclusion criteria were as follows: (a) nodules were metastatic focuses; (b) patients refused to participate in this study; (c) the clinical files were incomplete; (d) no specific records of CBCT employed or not; (e) patients were lost to follow-up; and (f) distance from nodules to pleura was less than 6 mm.
ENB-guided transbronchial MWA procedure
Before the initiation of treatment, a multidisciplinary team consultation involving thoracic surgery, pulmonology, oncology, and radiology should be conducted for the patient. The patient’s preferences should be fully taken into account, and the treatment plan should be selected based on the principle of maximizing the patient’s benefit.
As shown in Figure 2, the procedure was performed in a hybrid operating room with the patient in the supine position on a carbon fiber table equipped with an electromagnetic positioning plate. After general anesthesia was administered, a laryngeal mask airway (LMA) was placed, and electromagnetic sensors were attached to the chest wall. If the CBCT system (Cios Spin; Siemens, Erlangen, Germany) was used, an initial high-resolution CBCT scan was performed to confirm target lesions.

The procedure of ENB-guided transbronchial MWA. After evaluation and preparation, ENB is conducted to reach the target. In the non-CBCT group, the r-EBUS probe will be employed to confirm the position of the catheter. In the CBCT group, CBCT will be employed to confirm the position of the catheter, and r-EBUS might be employed to check blood flow when needed. After the catheter position is checked, MWA will be conducted. In the CBCT group, another CBCT scan will be conducted to confirm the ablation zone, though the non-CBCT group will not. Post-operation CT will be conducted to confirm the ablation outcomes.
The bronchoscope with a navigation catheter was then inserted into the LMA for preliminary airway inspection and ENB system registration (superDimension Navigation System, version 7.0; Medtronic, Minneapolis, MN, USA). The navigation system guided the catheter to the target lesion along a preplanned optimal path. If CBCT was used, a second scan confirmed the catheter position, and the r-EBUS probe (UM-S20-17S, Olympus Corporation, Japan) might be used for blood flow detection when needed; if not, r-EBUS probe was used to confirm the catheter position. If necessary, the catheter was repositioned for optimal placement. Once the position was verified, the navigation catheter was replaced with an ablation catheter, and MWA was initiated with a microwave generator (MTC-3; VISON-MEDICAL, Nanjing, China) operating at a frequency of 2450 ± 50 MHz and power of 40–80 W for 2–4 min per site, depending on tumor size, shape, and pleura proximity. A third CBCT scan, if employed, verified that the ablation zone covered the target lesion. Additional ablations and CBCT scans were performed as needed.
Before a CBCT scan, the anesthesiologist should manually inflate the lungs to obtain a positive end-expiratory pressure (PEEP) of above 20 mmH2O to ensure full lung expansion and pause the mechanical ventilation until the scan is done. Following ablation, the patient was revived and either transferred to the ward or proceeded with further scheduled treatments.
Statistical analysis
Data were presented as median (range) for continuous variables and as the counts (percentage) for categorical variables. Group differences were assessed using the Kruskal–Wallis test for continuous variables and the Chi-squared test, Yate’s adjusted Chi-squared test, or Fisher’s exact test for categorical variables, with a significance threshold of p < 0.05. Analyses were conducted using R version 4.4.1.
Results
Patient characteristics
As shown in Figure 2, a total of 476 medical records were retrieved. After screening, 58, 29, 81, and 7 records were excluded due to incomplete data, no specific records of the employment of CBCT, loss or lack of follow-up, or patients refused to participate, respectively, remaining 301 patients for further analysis. Based on the employment of CBCT during ablation, patients were divided into the CBCT group and the non-CBCT group, resulting in 83 patients in the CBCT group, and 218 patients in the non-CBCT group.
The patient characteristics including sex, age, height, weight, smoking history, comorbidities, Eastern Cooperative Oncology Group (ECOG) performance status, pulmonary function test (PFT) results, and counts of nodules planned to be ablated were compared between two groups. The results are summarized in Table 1. No significant differences were identified between two groups.
Patient characteristics.
CBCT, cone-beam computed tomography; COPD, chronic obstructive pulmonary disease; ECOG, Eastern Cooperative Oncology Group; FEV1, forced expiratory volume in the first second; FEV1/FVC, the ratio of FEV1 to FVC; FVC, forced vital capacity.
Nodule characteristics
A total of 389 nodules were included in the study since multiple nodules were planned to be ablated in some patients. In all, 118 and 271 nodules were allocated into the CBCT group and non-CBCT group, respectively. The characteristics of the nodules including nodule size, nodule position, nodule density category, and distance from nodules to pleura or fissure are shown in Table 2. Nodule size was significantly larger in the CBCT-employed group (8 mm vs 7 mm, p = 0.004). No significant differences were found in other characteristics between the two groups.
Nodule characteristics.
CBCT, cone-beam computed tomography.
Details and outcomes of ENB-guided transbronchial MWA
In all, 10 nodules in the CBCT group and 8 nodules in the non-CBCT group failed to be reached during the procedure. The technical success rate was significantly higher in the CBCT group compared to that in the non-CBCT group (97.1% vs 91.5%, p = 0.034). The rest of the nodules were ablated.
Details and outcomes of the ENB-guided transbronchial MWA procedure are presented in Table 3. Compared to the non-CBCT group, more nodules required multiple attempts to reach the target in the CBCT group (p < 0.001), the median ablation power was higher in the CBCT group (p < 0.001), more multiple ablations were conducted in the CBCT group (p < 0.001), resulting in different distribution of ablation duration (p = 0.001), longer procedure duration (p = 0.004), and larger ablation zone size in the CBCT group (p < 0.001). Ablation success was evaluated through postoperative CT images. The ablation success rate was significantly higher in the CBCT group compared to the non-CBCT group (90.9% vs 81.5%, p = 0.018). The ablation success rate of pure ground-glass nodules was 91.3% (168/184) in the CBCT group and 78.5% (62/79) in the non-CBCT group (p = 0.007), of part-solid nodules was 87.3% (55/63) in the CBCT group and 86.4% (19/22) in the non-CBCT group (p > 0.999), and of solid nodules were 100% for both groups. The ablation success rate of nodules smaller than 10 mm was 91.8% (169/184) in the CBCT group and 81.4% (70/86) in the non-CBCT group (p = 0.021), and of nodules equal to or larger than 10 mm was 88.6% (70/79) in the CBCT group and 81.8% (18/22) in the non-CBCT group (p > 0.999).
Details and outcomes of electromagnetic navigation-guided transbronchial microwave ablation.
CBCT: cone-beam computed tomography.
Safety and follow-up outcomes
As shown in Table 4, the complication rate was 4.1% in the non-CBCT group and 7.6% in the CBCT group, no significant difference was found between the two groups. Perioperative complications were observed in 19 patients, mostly mild, including pneumothorax (1 in the non-CBCT group and 3 in the CBCT group), which was fixed following VATS; intrapulmonary hemorrhage (5 in the CBCT group), which was self-healed or cured by hemostatic; and mild infection (2 in the non-CBCT group and 5 in the CBCT group), which was cured by antibiotics. Two patients in the CBCT group developed pulmonary abscesses requiring prolonged antibiotic treatment, and one patient acquired a bronchopleural fistula, necessitating surgery to fix.
Safety and follow-up outcomes.
CBCT, cone-beam computed tomography.
The operation of the two groups was completed in different time periods because CBCT was introduced to our clinical center later than ENB-guided transbronchial MWA. Hence, the follow-up duration of the CBCT group was significantly shorter compared to the non-CBCT group (18 months vs 41 months, p < 0.001). During follow-up, 61 patients in the non-CBCT group and 183 patients in the CBCT group reported no significant discomfort post-operation. No patient died during follow-up. One patient in the CBCT group with mixed ground-glass nodule failed to be ablated showed progression 6 months postoperatively and required VATS resection. No other progression or recurrence was found. Another patient in the CBCT group developed an infection around the ablation site 6 months post-procedure. The median count of CBCT scans was 4 times (range from 3 to 7). 37 patients reported discomforts, including persistent cough (1 in the non-CBCT group and 4 in the CBCT group), pain near the surgical site (4 in the non-CBCT group and 4 in the CBCT group), and reduced exercise tolerance (7 in the non-CBCT and 17 in the CBCT group). No cases of radiation-induced disease were reported.
Discussion
This study represents the largest-scale evaluation to date of CBCT employment in ENB-guided transbronchial MWA. While some clinical centers have adopted CBCT, no studies have systematically assessed whether it is essential in ENB-guided MWA or its associated benefits and limitations. Through a retrospective review of 301 patients treated with this technique, we found that CBCT use was significantly associated with higher technical and ablation success rates, especially for pure ground-glass nodules and nodules smaller than 10 mm, supporting its feasibility and efficacy in this context.
CBCT is increasingly recognized as a valuable tool in ENB-guided MWA. First, combining ENB and CBCT allows for optimal use of both technologies. ENB provides real-time guidance to the target, facilitating precise catheter placement via a pre-planned path, while CBCT offers direct visualization, allowing operators to confirm catheter placement and adjust as needed. Although using CBCT may require more positional adjustments, potentially extending the procedure time, it minimizes unnecessary catheter manipulation, aligning with findings from ENB-guided biopsy studies. 12
Second, CBCT enables immediate visualization of the ablation zone post-MWA, allowing operators to verify ablation adequacy and conduct additional ablations if needed in the same session. This capability is crucial, as the ablation zone size can be difficult to predict based on pre-planned power and duration alone. 17 Without CBCT, outcome confirmation would require post-procedural CT, potentially necessitating a second operation. Although CBCT provides immediate confirmation, local exudation or hemorrhage can still mimic the necrosis zone, occasionally resulting in incomplete ablation.
In addition, CBCT can serve as a backup when ENB navigation fails. In some cases, the navigation system misrepresented the catheter’s position, but with CBCT, we successfully reached targets despite ENB inaccuracy. These issues often stem from discrepancies between preoperative CT (with the lung fully expanded by breath-hold) and intraoperative lung conditions (ventilated by lower pressures), particularly in the lower lobes where the lung is more proteiform. In our clinical center, when preparing for a CBCT scan, we will pause ventilation and temporarily increase the PEEP to above 20 mmH2O to ensure full lung expansion. CBCT also helps confirm adequate lung expansion and indicates the adjustment of PEEP, supporting successful navigation. Shape-sensing robotic bronchoscopy might help further reduce the influence of CT-to-body discrepancies and increase the technical success rate theoretically due to its improved airway accessibility and excellent stability, which has shown superiority in transbronchial biopsy. 18
CBCT further streamlines procedures for patients needing hybrid operations, such as VATS and MWA for multiple nodules, by enabling one-stop solutions under a single anesthesia in one room. Some centers use standard CT instead of CBCT, necessitating patient transfers, which increases time and risk. A study comparing regular CT-guided and CBCT-guided transbronchial lung nodule biopsy has preliminarily demonstrated that CBCT guidance can achieve a higher diagnostic yield and shorter operation time. 19 Similarly, compared to regular CT, the use of CBCT might achieve a higher ablation success rate likewise. When employing regular CT, after guiding the working catheter to the target position, the bronchoscope needs to be repositioned for CT scanning, and the patient will move with the CT examination table during scanning. Various steps in this process may cause the working catheter to shift and spend more time. During CBCT scanning, only the C-arm moves, while the patient, bronchoscope, and working catheter can be well fixed, providing higher stability. Therefore, the employment of CBCT should achieve a higher ablation success rate theoretically, although further research is required to confirm this view.
Our findings suggest that CBCT does not increase complication rates. However, in the CBCT group, two patients developed post-procedural pulmonary abscesses, and one had an infection progressing to bronchopleural fistula, requiring surgery. All three cases had received multiple ablations in one area, forming large postoperative cavities conducive to abscess formation. As a preventive measure, prophylactic antibiotics should be administered, especially for patients undergoing multiple ablations. One patient also experienced delayed infection 6 months post-procedure, indicating that infection risk may persist. Hence, regular follow-up is necessary.
Moreover, no radiation-induced complications were reported in this study. Another benefit of CBCT is its relatively low radiation dosage. In our clinical center, the dose area product (DAP) was within the range of 500–900 μGy·m2, and the effective dosage of patients for one scan should not exceed 3 mSv, which should be much lower than a standard high-resolution chest CT scan (approximately 9 mSv).20 –22 However, excessive adjustments could increase radiation exposure, underscoring the importance of minimizing scans when possible. Given the study’s limited follow-up period, the potential long-term effects of radiation remain uncertain.
As a retrospective study, this research has inherent limitations. The sample size, although larger than previous studies, is still restricted to a single center, introducing potential bias. In addition, the short follow-up period precludes insights into long-term outcomes. Future large-scale, multi-center, prospective studies with extended follow-up are needed to confirm these findings and evaluate the long-term efficacy and safety of CBCT in ENB-guided MWA. Furthermore, we noticed that the ablation success rate for solid nodules was 100%, where bias might exist. Due to the similar imaging density, it may be difficult to distinguish between the ablation area and the solid nodule even if ablation is unsuccessful, which may lead to a misjudgment of successful ablation.
Conclusion
Employing CBCT during ENB-guided transbronchial MWA for pulmonary nodules may significantly enhance the ablation success rate, while the complication rates remain comparable to those of procedures without CBCT. These findings highlight the potential benefits of integrating CBCT into the ablation process. However, further validation through large-scale, multi-center, prospective studies with extended follow-up periods is essential to confirm these results.
Supplemental Material
sj-docx-1-tar-10.1177_17534666251333287 – Supplemental material for Improving outcomes in electromagnetic navigation bronchoscopy-guided transbronchial microwave ablation for pulmonary nodules: the role of cone-beam computed tomography
Supplemental material, sj-docx-1-tar-10.1177_17534666251333287 for Improving outcomes in electromagnetic navigation bronchoscopy-guided transbronchial microwave ablation for pulmonary nodules: the role of cone-beam computed tomography by Yaochen Huang, Lin Zhou, Yongyong Wang, Jianing Wang, Zhipeng Hao and Xiangning Fu in Therapeutic Advances in Respiratory Disease
Footnotes
References
Supplementary Material
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