In the 8 rabbits that underwent transbronchial RFA, there was 1 incidence of hemothorax and no incidence of pneumothorax or thermal injury to the chest wall.
Percutaneous, image-guided RFA has been successfully applied to local control in various locations, including bone, liver, kidney, and lung. However, large pneumothorax or persistent hemoptysis are potential complications when this procedure is used to treat lung cancer. In a study of 30 patients who underwent CT-guided RFA to treat lung cancer, pneumothorax was the most common complication and occurred more frequently in patients whose tumors were located in the central portion (inner two thirds) of the lung compared with those whose tumors were located in the peripheral portion (outer one third) of the lung.16 At present, the greatest clinical use of CT-guided RFA is for the treatment of small peripheral lung tumors in patients who are poor candidates for surgery. However, if the incidence of pneumothorax could be reduced, more patients may benefit from RFA therapy. The transbronchial approach for RFA may potentially develop into a minimally invasive therapy with a low frequency of pneumothorax that can be used to treat patients with inoperable lung tumors located within either the central or peripheral areas of the lung.
To our knowledge, this is the first report of the transbronchial approach for RFA treatment of lung tumors. The transbronchial approach has several advantages over the percutaneous approach. First, because the transbronchial approach does not puncture the chest wall, the risk of pneumothorax and hemothorax due to injury of the intercostal or chest wall vessels is reduced. Second, the transbronchial approach can more readily be used to treat tumors that are located in the central portion of the lung, where use of the percutaneous approach may result in an unacceptably high rate of pneumothorax. Third, because the transbronchial approach is minimally invasive, it can more readily be used repeatedly, in contrast to percutaneous RFA. A disadvantage of the transbronchial approach is that it can be difficult to reach and treat small, peripherally located tumors. In these cases, a navigation system17 or endobronchial ultrasound system18 may be helpful.
There were some limitations in this study. First, the number of rabbits was too small to definitively analyze the effectiveness or potential complications of the procedure. Second, the probe was not sufficiently powerful to ablate effectively using the transbronchial approach because of the still small area of ablation, and probe improvement will be needed to optimize the settings. Currently, the upper limit of homogeneous tissue ablation for most RFA systems operating in living tissue is between 4 and 5 cm in diameter. Our results showed 8 mm in diameter of ablation with 20 minutes of exposure at 2 W/min. When a tumor larger than 8 mm is treated at the time of improvement of the probe, the risk of hemorrhage or hemothorax might be higher. Crocetti et al19 compared feasibility and safety of microwave and RFA of the lung tissue in a rabbit model. In this study, the small vessel occlusion including thrombosis by RFA was much less than microwave ablation. Third, the tumor location was limited to the right lower lobe in this study, because a flexible bronchoscope that could reach other locations, particularly an upper lobe, could not be used in small animals. Lastly, this study could not examine the survival rate after RFA therapy. However, it is generally difficult to evaluate the survival rate using an animal model of VX2 tumors, because this tumor line is extremely malignant.20 This experimental study demonstrates that transbronchial RFA therapy could be a feasible, safe, and effective therapy for treating lung VX2 tumors in a rabbit model, although improvement of the probe will be required for further investigation. Additional experiments are needed to optimize a technique that can be used for clinical therapy.
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