Image-Guided Ablation as a Treatment Option for Thoracic Malignancies

Patient Evaluation

Patients referred for RFA are initially evaluated in a clinic where the patient’s history and pertinent imaging studies are reviewed. During this initial visit, the appropriateness of the RFA procedure, as well as the risks and benefits of the procedure are discussed with the patient and family. All preprocedural studies are ordered. Risks such as bleeding or serious cardiopulmonary issues are addressed, as are the side effects of the RFA, which includes the postablation syndrome. The postablation syndrome is a transient systemic response to the circulating factors such as tumor necrosis factor that results in fever, malaise, and anorexia.

Generally, most patients who are stable enough to undergo computed tomography (CT)-guided needle biopsy are good candidates for pulmonary RFA. Special attention is paid to those patients who only have a single lung remaining and have severe emphysema. Patients with a single lung may need a chest tube after the RFA procedure. Patients with severe emphysema may retain carbon dioxide and lose their respiratory drive. Patients with idiopathic pulmonary fibrosis are considered poor candidates for the pulmonary RFA procedure because exacerbation of the underlying disease may lead to serious respiratory failure and possible death following the RFA procedure.

All patients are told to fast the night before the procedure to limit the risk of sedation-induced nausea and aspiration of gastric contents. Patients with hypertension and cardiac disease are told to take their medications as usual. Insulin-dependent diabetic patients are asked to administer only half of their usual morning insulin dose.

Technique

When the patient arrives at the department, a brief history and physical examination is performed. An intravenous line is placed. Patients are brought to the CT scanner whereby the CT technical staff prepare the patient for the procedure. The appropriate grounding pads are placed on the opposite chest wall from the skin entry site to direct the RF current and prevent damage to adjacent structures in the target area. The site of skin entry is determined using a computer grid after the initial preprocedure images are obtained. The desired skin entry site is matched with the site determined on the computer screen using the horizontal and vertical laser lights in the CT gantry. The skin is prepped and draped in a sterile fashion. A 1% buffered lidocaine hydrochloride solution is used for local anesthesia at the skin and down to the extrapleural soft tissues. Using CT-guided fluoroscopy, the needle tip is identified. A small skin incision is made approximately 1-2 cm into the subcutaneous tissues. The RF electrode is placed through the skin and pleura approximately one-half to two-thirds the distance to the target lesion. The RF electrode angle is corrected as necessary using CT-guided fluoroscopy.

For pleural-based masses, preference is for the shorter RF electrode. Superficial positioning of the electrodes may be difficult from a lateral position due to the protrusion of the electrode in the CT gantry if the gantry is narrow (e.g., 70 cm). A coaxial guiding catheter could also be used in this situation, in which the RF electrode is placed into the mass all at once, after the outer cannula position is confirmed. Central and distal positioning of the RF electrode is adequate for the first ablation for lesions less than 2 cm. The ideal positioning in all RF ablation procedures is along the longitudinal axis so that sequential overlapping tandem ablations can be performed during electrode withdrawal. Lesions larger than 2 cm require larger electrode or several overlapping ablation zones to be performed for adequate thermocoagulation of the target lesion.

The optimal ablative temperature to achieve thermal injury and immediate cell death is 60°-100°C throughout the target volume in a controlled setting. Energy generated during the RFA procedure is accumulated within the lung mass because the normal lung parenchyma acts as an insulator and therefore concentrates the RF energy in the target tissue. There is also a heat sink effect, which dissipates heat away from the normal adjacent tissue and concentrates the energy within the solid component of the target lesion. This same effect may limit successful RFA of larger lesions.

Like for liver tumor ablations, it is best to work around the periphery of larger tumors in the lung to ensure adequate ablation of the soft tissue margins. Large lung tumor ablation procedures require less time and current to achieve adequate thermocoagulation than in liver masses. This may be a result of limited current deposition within small parenchymal masses surrounded by aerated lung. Each ablation should follow the manufacturer’s guidelines regarding temperature and/or impedance ( Box 27-2 ).

Conscious sedation is maintained with doses of midazolam (0.5 mg intravenously) and fentanyl (25-50 μg intravenously) during the RF ablation procedure. The nursing staff continuously monitor the patient’s vital signs and electrocardiogram throughout the procedure. Generally, pulmonary lesions located away from the visceral pleura require less sedation than painful pleural based lesions. VanSonnenberg and colleagues report using intercostal and paravertebral nerve blocks with long-acting local anesthetic to prevent postprocedural discomfort and pain. RF heating of central lesions near the bronchi may produce a prominent cough response and as a result may require more sedation to prevent patient motion. Vagal nerve stimulation may produce referred pain to the jaw, teeth, chest, or upper extremity similar to pain related to a myocardial ischemic event. If the patient becomes bradycardic, 0.5-mg doses of atropine may be administered. General anesthesia may be necessary for pediatric patients or patients who do not tolerate the RF heating with conscious sedation alone. Dual lumen endotracheal tubes are generally not necessary; given the coagulating effect of the RF current, bleeding related to the RFA procedure is similar to or less than that which occurs with CT-guided biopsies.

Once the target lesion is treated, the RF electrodes are removed and CT-guided fluoroscopy is performed to exclude a pneumothorax. Small asymptomatic pneumothoraces are monitored with immediate and 2-hour postprocedure chest radiographs. These patients are monitored in the recovery room on oxygen for at least 2 hours after the procedure. If the 2-hour postablation chest radiograph demonstrates an increasing pneumothorax or the patient is symptomatic, then a chest catheter is placed and wall suction evacuation is done. If there is interval resolution of the pneumothorax after chest tube placement, the patient is discharged home with a Heimlich valve on the end of the catheter and is told to return in 24 hours for a repeat chest radiograph. Patients are instructed to immediately report any shortness of breath, bloody sputum, or pain. Hospitalization may be required for pain or if the patient is reluctant about outpatient chest tube management. If the pneumothorax is resolved on follow-up, the chest tube is checked for an air leak by having the patient cough with the tube end in a container of sterile water. If no air bubbles are seen, the chest tube is removed with petroleum jelly–based gauze to provide an airtight seal upon removal. Patients with air leaks may require prolonged hospitalization and placement of a surgical chest tube.