Portable Cone-Beam Computed Tomography System for Intraoperative Localization of Pulmonary Nodules: An Initial Experience

Abstract

Objectives

Advances in imaging have expanded options for diagnosis and therapy, including wedge resection of small pulmonary nodules. Cone-beam computed tomography (CBCT) can substitute for hybrid operating rooms (ORs) to identify impalpable nodules. We report the initial clinical use of a portable CBCT system (Cios Spin, Siemens, Germany) for intraoperative localization of small pulmonary nodules.

Methods

Four patients (3 men, 1 woman; mean age, 68.3 years) with peripheral nodules were included. Under general anaesthesia, an initial pre-scan confirmed that the lesion was within the field of view. Thoracoscopic surgery was initiated, and a surgical clip was placed on the visceral pleura at the site predicted from preoperative computed tomography (CT) to be closest to the tumour. During surgery, the C-arm was removed and later repositioned for intraoperative scanning.

Results

All nodules, 1.4-cm ground-glass, 2.0-cm part-solid, and two 0.7-cm, were clearly visualized, with image quality comparable to preoperative CT. The portable system accommodated table flexion and lateral decubitus positioning. No complications occurred, and radiation exposure, measured in one case, was acceptable.

Conclusions

To our knowledge, this is the first report to demonstrate that portable CBCT enables accurate, flexible, and real-time intraoperative localization of pulmonary nodules without requiring a hybrid OR.

The intraoperative localization of small pulmonary nodules remains a challenge in general thoracic surgery, especially in wedge resection of the lungs.

INTRODUCTION

The intraoperative localization of small pulmonary nodules remains a challenge in general thoracic surgery, especially in wedge resection of the lungs. Recently, cone-beam computed tomography (CBCT) has been proven effective in hybrid operating rooms (ORs).^1–3 However, this procedure has been used only in hybrid ORs, where patient-positioning options are limited. In this report, we describe our initial experience with portable CBCT, in which small nodules were clearly visualized using this previously reported technique in thoracic surgery,² and we assess whether positioning flexibility can be improved.

MATERIALS AND METHODS

This retrospective case series describes our initial clinical experience using a portable CBCT system for intraoperative lung nodule localization. All procedures were part of routine intraoperative lung nodule marking conducted under Institutional Review Board (IRB) oversight, with written informed consent obtained from all patients prior to surgery. This study was approved by the IRB of Kurume University Hospital (approval number: 20008).

Four patients (3 men and 1 woman; mean age 68.3 years) with peripheral pulmonary nodules (0.7–2.0 cm in diameter) were enrolled in the study (Table 1). Body mass index ranged from 18.3 to 23.1; no patient had an overly large physique. All nodules were suspected to be malignant and predicted to be non-palpable. With IRB approval and patient consent, a portable CBCT system (Cios Spin, Siemens, Germany) and a flexible surgical table (MOT-VS600, Mizuho, Japan) were used.

Table 1.

Patient Characteristics and Outcomes

No.	Age	Sex	Height (cm)	Weight (kg)	BMI	Size of nodule (cm)	CT imaging findings	Preoperative csuspicion	Procedure	Final pathological diagnosis
1	64	M	168.3	63.0	22.3	0.7	Pure solid nodule	Metastasis from chordoma	Wedge resection: left lower lobe	Metastasis from chordoma
2	76	F	150.0	44.0	19.6	2.0	Part-solid GGN	Invasive adenocarcinoma	Lobectomy: right lower lobe	Minimally invasive adenocarcinoma
3	69	M	170.0	53.0	18.3	1.1	Pure GGN	Adenocarcinoma in situ	Segmentectomy: left upper division	Minimally invasive adenocarcinoma
4	64	M	165.7	63.7	23.1	0.7	Pure solid nodule	Metastasis from lung cancer	Segmentectomy: right segment 6	Squamous cell carcinoma

Abbreviations: BMI: body mass index; GGN: ground-glass nodule.

Under general anaesthesia, the patient was placed in the lateral decubitus position, and a temporary skin-marker (eraser piece) was placed at the site predicted to be closest to the tumour. A pre-scan confirmed that the lesion was within the C-arm’s field of view. After marking the C-arm position on the floor, the arm was removed and thoracoscopic surgery was initiated. A surgical clip was placed on the visceral pleura at the site predicted to be nearest the tumour. A second CBCT scan was then performed to assess the clip-tumour positional relationship; if misaligned, the clip was repositioned and the scan repeated. Once accurate tumour localization was confirmed, the C-arm was removed and a wedge resection was carried out. This procedure was based on our previously reported method for fixed CBCT systems,² with the primary innovation being the use of a portable CBCT unit.

A large prospective series of approximately 30 cases is planned to validate this approach.

RESULTS

In all 4 cases, the nodules were successfully localized and resected. All lesions were impalpable and exhibited no pleural surface changes. They were small or located slightly beneath the pleural surface and thus could not be identified without intraoperative CBCT. In one case, a pure GGN (1.4 cm) was visible. No intra- or postoperative complications were observed. In one patient, lobectomy was performed following confirmation of malignancy through intraoperative frozen section.

All lesions were visualized on intraoperative CBCT, including 1 GGN (case 3) and 2 sub-centimetre nodules (cases 1 and 4). As shown in Figure 1, the image quality of the intraoperative CBCT was comparable to that of preoperative CT, allowing for reliable localization of subtle lesions without requiring hybrid OR facilities. The final diagnoses included 2 cases of minimally invasive adenocarcinoma, one case of squamous cell carcinoma in the right lower lobe (metastasis from left upper lobe lung cancer), and one case of metastatic chordoma.

Figure 1.

Comparison Between Preoperative Computed Tomography (CT) Imaging (A-C) and Intraoperative Portable Cone Beam CT (D–F) in the 4 Representative Cases. Each panel shows the same lesion visualized on preoperative CT (A: case 1, B: case 2, and C: case 3) and intraoperative CBCT (D-F, respectively). All nodules were clearly identifiable, including small nodules and pure ground-glass nodules.

Because a demonstration unit was used, the dose was measured only in case 3: 7.6 mGy for the first scan (standard mode), 22.6 mGy for the second scan (high quality mode), and 32.0 mGy total intraoperatively, including fluoroscopy. The mean time required to identify the lesion, including positioning, C-arm insertion and removal, and scanning time, was approximately 15 minutes.

DISCUSSION

Several previous studies^1–3 have demonstrated the utility of fixed CBCT in hybrid ORs. Conversely, our study shows that portable CBCT can provide comparable image quality and flexibility in standard ORs. To our knowledge, this is the first report on the use of portable CBCT for intraoperative localization of small pulmonary nodules. Although portable CBCT devices have been applied in other surgical fields, such as head and neck surgery, orthopaedics, and interventional pulmonology,^4,5 data on their use in thoracic surgery are lacking.

Regarding image quality, the target lesions were clearly visualized on intraoperative CBCT, even in case 3, which involved a 1.4 cm pure GGN without contrast enhancement, and in cases 1 and 4, which involved small nodules measuring only 0.7 cm. These results suggest that the image quality provided by intraoperative CBCT is sufficient for identifying pulmonary lesions typically targeted for wedge resection during thoracic surgery. Additional case studies are required to validate the clinical utility and consistency of this method.

To date, intraoperative CBCT has only been performed in a hybrid OR. Usually, when possible, nodules are predicted to be unpalpable, and it is necessary to schedule surgery in the hybrid OR; if the surgery takes place in the general OR and the surgeon wishes to confirm the presence of impalpable nodules, the CT imaging is not available. As a solution to this problem, the portable CBCT system allows for the confirmation of tumour location in the general OR, without having to plan for CBCT ahead of time.

Another limitation of fixed CBCT systems is the inflexibility of the operating table. We addressed this issue by combining table components to allow for bed flexion, which widens the intercostal space, facilitates port insertion, and improves scope manoeuvrability. This setup enables stress-free anatomical lung resection, including additional lobectomy, when needed, similar to conventional video-assisted thoracic surgery.

Moreover, the C-arm width of the Cios Spin (94 cm) exceeds that of standard units (typically approximately 79 cm), allowing easy use even in the lateral decubitus position.

Radiation dose was assessed only in case 3: 7.6 mGy in standard mode, 22.6 mGy in high quality mode, and a cumulative total of 32.0 mGy including fluoroscopic dose. Radiation exposure and procedural time tended to be lower than those reported for fixed CBCT systems (Kaiho et al, 2022), likely due to the simpler setup and limited scan range. The Cios Spin offers 4 modes: low dose, standard, high quality, and extra power, with higher modes providing better image quality at the cost of increased radiation. In future studies, the way in which lesion characteristics (eg, size and density) influence radiation exposure should be evaluated in order to optimize mode selection based on preoperative imaging.

CONCLUSION

This preliminary experience suggests that portable CBCT is a technically useful and promising tool for broader clinical application in intraoperative localization of pulmonary nodules, warranting further validation in larger studies.

AUTHOR CONTRIBUTIONS

Masahiro Mitsuoka conceived the study, performed the surgical procedure, and supervised the overall management. Nagiko Mitsuoka, as a resident, presented the study at the World Conference on Lung Cancer in San Diego in September 2024. The other 6 co-authors participated as primary or assistant physicians in the clinical management of the patients. All authors contributed to data interpretation and manuscript preparation.

FUNDING

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

CONFLICTS OF INTEREST

None declared.

DATA AVAILABILITY

All relevant clinical data supporting the findings of this study are included in the manuscript and its figures and tables. Due to patient privacy considerations, no additional raw data are available.