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a Department of Cardiothoracic Surgery, Boston University School of Medicine, Boston, Massachusetts
b Department of Radiology, Boston University School of Medicine, Boston, Massachusetts
c Instituto de Ensino e Pesquisa Albert Einstein, São Paulo, Brazil
Accepted for publication June 1, 2009.
* Address correspondence to Dr Fernando, 88 E Newton St, B-402, Robinson Bldg, Boston Medical Center, Boston, MA 02118 (Email: hiran.fernando{at}bmc.org).
Presented at the Poster Session of the Forty-fifth Annual Meeting of The Society of Thoracic Surgeons, San Francisco, CA, Jan 26–28, 2009.
| Dr Fernando discloses that he has a financial relationship with Veran Medical Technologies, Inc.
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Description: Ten patients undergoing lung percutaneous ablation were prospectively enrolled. The mean age was 70 years. Positioning of the needle device was verified with computed tomographic fluoroscopy prior to the execution of any biopsy or ablation. Each EM navigation-guided procedure was defined as an EM-intervention.
Evaluation: Nineteen EM interventions were performed. When an EM-guided biopsy was performed, the intervention was done immediately prior to ablation. For all 19 EM interventions, only one skin-puncture was required. The mean number of instrument adjustments required was 1.2 (range, 0 to 2). The mean time for each EM intervention was 5.2 minutes (range, 1 to 20 minutes). Pneumothorax occurred in 5 patients (50%). Only the number of instrument adjustments was significantly related to the pneumothorax rate (p = 0.005).
Conclusions: The EM navigation is feasible and seems to be a useful aid for image-guided procedures. Early experience suggests a low number of skin-puncture and instrument adjustments using the EM navigation system. Instrument adjustments were a key factor in pneumothorax development.
A number of solid organ tumors are increasingly treated with minimally invasive percutaneous techniques that include radiofrequency ablation (RFA), microwave ablation, and cryoablation [1]. Traditionally, image-guided procedures have been performed by interventional radiologists; however, with the development and introduction of these new oncological modalities, thoracic surgeons and surgical oncologists are either acquiring the skills to perform these procedures or partnering with interventional radiologists.
Percutaneous ablation of lung tumors is generally performed with computed tomography (CT) guidance. In a typical procedure, first, a baseline CT scan is performed to identify the lesion and the optimal route of access. Then the patient is removed from the CT gantry, and after review of the CT scan, a suitable entry site on the skin is marked. Subsequently, an ablation probe is advanced toward a target pulmonary lesion. As the ablation probe is advanced toward the lesion, serial CT scans are performed, requiring the patient to move in and out of the CT gantry and the staff to leave the room between each instrument adjustment (IA). A CT fluoroscopy has also been used in several institutions, but has not been universally adopted because of concerns of radiation exposure to staff. All personnel present during the operation of CT fluoroscopy must take precautions such as the use of lead aprons to protect themselves from radiation exposure.
Electromagnetic navigation has been previously reported to facilitate bronchoscopic procedures, such as biopsies for peripheral lung lesions or fiducial placement for stereotactic body radiotherapy [2]. The electromagnetic (EM) navigation is now being incorporated to assist with image-guided percutaneous interventions [3]. We report our initial experience using EM navigation to guide percutaneous placement of ablation probes and biopsy needles for patients with lung tumors. Our institutional review board approved this prospective, single-arm study; informed consent was obtained in all patients.
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Patients
There were 10 patients in this study with suspected or known lung cancer who underwent 19 EM interventions under general anesthesia. All patients were considered high risk for pulmonary resection, and percutaneous ablation was selected as the primary therapy. The EM interventions included biopsy and percutaneous ablation with RFA or microwave. Our preference is to usually perform biopsy prior to scheduling ablation; however, in some patients, where the risk of biopsy is considered high, a biopsy is performed immediately prior to ablation so that patients will be subjected only once to the risk of pneumothorax in a more controlled situation with anesthesiologists and thoracic surgeons present during the procedure.
Procedural Details
All procedures were performed using a 16-slice CT scanner with CT fluoroscopy (Lightspeed VCT [GE Healthcare, Waukesha, WI]). After general anesthesia, patients are placed in the optimal position for the ablation procedure (ie, usually the lateral decubitus position). Then EM tracking pads are placed on the patient's chest; these consisted of three pads placed in an L-shaped configuration (Fig 1) positioned in such a way that they would not interfere with placement of the ablation probe or a tube thoracostomy, if necessary, during the procedure. A CT scan is then obtained and the images are networked to the EM navigation system. The EM generator and tracking system is a portable unit with an articulated mechanical arm that can be wheeled up to the scanner and placed over the operative field during needle-probe placement.
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All biopsies performed were core biopsies; no fine-needle aspiration biopsies were undertaken. Median nodule diameter was 1.95 cm (1.2 to 2.4 cm), and median distance from the skin to lesion was 7.6 cm (2 to 18 cm). Median BMI was 24.1 (20.8 to 46.6).
For the 19 EM-guided interventions, a single skin puncture was required. The median and mean number of IAs required were 1 and 1.2, respectively (range 0-2). The median and mean time for each EM intervention was 4 and 5.2 minutes, respectively (range, 1 to 20 minutes). The BMI, nodule diameter, skin-to-lesion distance, and development of pneumothorax were analyzed to determine their impact on the time for the EM intervention. None were found to have any significant effect.
The pneumothorax was observed in 5 patients (50%); all were treated with a pigtail placement. Analysis was undertaken to determine which of the following variables influenced the incidence of pneumothorax: diameter of nodule, skin-to-lesion distance, BMI, the number of IA for each intervention, the number of interventions in each patient, and whether the core biopsy was undertaken. Of these, only the number of IAs significantly increased (p = 0.005) the incidence of pneumothorax. A mean of 1.8 IAs was required to achieve optimal device placement in patients who had a pneumothorax develop compared with 0.6 IAs in patients who did not. Mean and median length of stay was 3.9 and 1.5 days, respectively. Mean length of stay was significantly longer (p = 0.025) when a pneumothorax occurred at 6.6 days compared with 1.2 days. None of the patients who received a pigtail or chest tube required any additional procedure or had any other associated morbidities. No other significant complications occurred in this series.
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One significant disadvantage of using the contrast-enhanced CT scan is that the intravenous contrast used to outline vascular structures is generally limited to the initial planning CT scan. Subsequent needle placement and adjustments are then performed after the intravascular contrast has washed out (usually within 2 to 3 minutes). The use of EM navigation may overcome or minimize some of these issues by using a contrast-enhanced scan for navigation.
In our series the mean number of IAs was 1.2. Although this was a single arm study, we have found that for procedures using CT fluoroscopy alone, a greater number of IAs (approximately 8 [unpublished data]) will be required. It is also likely that CT fluoroscopy time will be increased in those patients requiring a greater number of IAs.
The EM system works by emitting very low-frequency EM waves (approximately 40 kHz), and there is no known interaction with human tissue. The use of EM navigation for interventional bronchoscopy has been previously reported [6].
In contrast to bronchoscopic navigation, there have been relatively few reports on the use of percutaneous EM navigation. In one study of 20 patients (including 10 lung tumors), EM navigation was successful in 19 patients (95%) [7]; mean lesion size was 26.5 mm. No complications occurred, and all biopsies were deemed technically successful.
One of the most common complications after percutaneous thoracic interventions is pneumothorax. The risk of pneumothorax for percutaneous pulmonary interventions has been previously reported to be related to the degree of emphysema, the length of aerated lung traversed during the procedure, the number of needle passes through the pleura, and also the number of needle-device adjustments during the procedure [8]. In another study [9], the risk factors for pneumothorax were analyzed in 356 patients after transthoracic needle aspiration biopsy. The authors concluded that the factors affecting the risk of pneumothorax were lesion size and the presence of emphysema. Patients with emphysema were three times as likely to require chest tube placement. However, if no aerated lung was traversed during needle penetration, the pneumothorax rate was low.
The pneumothorax rate in our study was 50%. Previous studies have demonstrated pneumothorax rates of between 12% and 63% after RFA. The differences between series may have been influenced by the choice of ablation probe, the number of probe placements, and whether biopsies were performed at the same time as the ablations. In our study, 70% of our patients underwent a biopsy with a cutting needle at the same time as their ablation
In conclusion, EM navigation has been demonstrated to be feasible and a useful adjunct to aid image-guided interventions for small pulmonary tumors. A minimal number of IAs were required for successful completion of each percutaneous intervention.
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This article has been cited by other articles:
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  L. Appelbaum, J. Sosna, Y. Nissenbaum, A. Benshtein, and S. N. Goldberg Electromagnetic Navigation System for CT-Guided Biopsy of Small Lesions Am. J. Roentgenol., May 1, 2011; 196(5): 1194 - 1200. [Abstract] [Full Text] [PDF]
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 C. A. Buckner, A. Venkatesan, J. K. Locklin, and B. J. Wood Real-time Sonography With Electromagnetic Tracking Navigation for Biopsy of a Hepatic Neoplasm Seen Only on Arterial Phase Computed Tomography J. Ultrasound Med., February 1, 2011; 30(2): 253 - 256. [Abstract] [Full Text] [PDF]
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