Division of Thoracic Surgery
Maimonides Medical Center
Brooklyn, NY
Lung cancer is currently the most common cause of adult cancer related to mortality in the United States. Surgical resection remains the gold standard therapy for resectable disease and offers the best chance for a cure. Unfortunately, age, poor lung function, and significant comorbidity preclude many patients with otherwise resectable lung cancer from surgical therapy. A conventional option for medically inoperable patients with lung cancer includes external beam radiation therapy. Long-term survival with this treatment modality is poor, with reported 5-year survival rates from 10% to 30% and 13% for stage I non-small cell lung cancer (NSCLC) (Sibley et al. Int J Radiat Oncol Biol Phys. 1998;40[1]:149).
The need to improve the treatment of this high-risk group of patients with lung cancer has prompted the development of newer treatment modalities as alternatives to conventional therapy. Radiofrequency ablation (RFA) and stereotactic radiosurgery (SRS) are two such alternative modalities that have emerged in the arena of lung cancer treatment in recent years. RFA has historically been used as an adjunct for treatment of tumors of solid abdominal viscera, and its use for pulmonary malignancy was first reported in 2000. Since that time, multiple case series have been published establishing the safety and efficacy of this treatment modality for pulmonary malignancies in high-risk patients.
SRS was a term originally coined by Leksell to describe a radiation delivery system in which multiple convergent beams of radiation could be delivered to a tumor, utilizing a three-dimensional imaging localization technique. This modality was originally applied to intracranial malignancies, and in 1994, was adapted to treat extracranial lesions as well (Song et al. Oncology. 2004;18[11]:1419). Several reports of its use for pulmonary malignancies began to emerge in the early 2000s; and since that time, refinement of imaging, tracking, and radiation delivery systems has given rise to several different commercially available SRS systems. One such system that has shown success in the treatment of pulmonary malignancy is the CyberKnife® System (Accuray, Sunnyvale, CA).
Radiofrequency Ablation
RFA utilizes heat-induced cellular necrosis and is administered by means of an alternating current applied via an electrode. The current is supplied by a radiofrequency generator and is transferred through the patient and completed via two grounding pads. The alternating current, when applied to tissue, results in agitation of water molecules and frictional release of thermal energy within the immediate area of the electrode. At 46°C cell death occurs within 60 minutes, at 50°C to 52°C irreversible cell death occurs at 4 to 6 minutes, and at 60°C there is instantaneous irreversible cell death.
The goal of RFA is to ablate the tumor with a 0.5- to 1.0-cm margin of surrounding lung tissue. The RFA electrode, with or without tines deployed, ablates a spherical target area of tissue. The target temperature during a conventional pulmonary RFA treatment protocol is 105°C. For an electrode with multiple tines, the temperature is typically averaged across all tines, which each provide accurate real-time temperature readings at their respective locations within the tissue.
Indications for pulmonary RFA include otherwise resectable pulmonary nodules in patients who either refuse surgery or are at high risk for surgical resection. This includes patients with poor pulmonary reserve and/or medically inoperable patients, such as those who have severe coronary/valvular disease, uncompensated congestive heart failure, or other severe comorbidities, who are candidates for RFA. Patients who have failed prior modalities, including surgical resection with or without chemoradiation, would also qualify for RFA treatment.
The only absolute contraindication to RFA is a central location of a nodule, defined as being within 3 cm of the hilum. Central nodules are close to large blood vessels, which function as heat sinks, limiting the therapeutic effect of RFA. Also, the presence of larger airways with corresponding pulmonary vessels near the hilum increases the risk of potentially lethal bronchovascular fistula formation from ablation. Relative contraindications include large nodules (>3 cm) that would require multiple ablations within the same nodule as well as multiple nodules. The latter may be cumbersome to treat and may not be technically feasible, although multiple staged treatments for bilateral pulmonary nodules are possible.
The procedure of RFA for pulmonary lesions with regard to electrode placement and treatment algorithm varies according to the protocols supplied by the individual RFA system manufacturers. Either general endotracheal anesthesia or local with intravenous sedation may be used. The latter generally decreases the risk of pneumothorax with the trade-off that the patient is more likely to move spontaneously during the procedure. Typically, the electrode is placed under image guidance into the center of the nodule after a small skin incision is made to accommodate the 14-gauge needle. Imaging should be repeated between every repositioning to confirm placement. In the event of a periprocedural pneumothorax, a pleural drainage catheter should be placed immediately to evacuate it, as this may cause the lung and nodule to fall away from the chest wall and impede adequate placement of the electrode. A completion CT scan is performed after treatment to visualize the adequacy of the ablation as well as to visualize delayed pneumothorax formation. Occasionally, fiber-optic bronchoscopy may be required to clear endobronchial secretions, which can be blood-tinged after treatment.