Postoperatively, the patient is typically admitted for observation overnight. Chest radiographs are obtained at 6 h postoperatively and the following morning to assess for delayed pneumothorax. If a chest pigtail was required during or after the procedure, a clamp trial is usually performed the following day prior to removal. Rarely, a patient will require a chest drain for a longer period of time, resulting in a prolonged hospital stay. A follow-up chest CT scan may be done the next morning to more accurately assess the post ablation lung but is not required. Patients are typically followed with CT/PET scans at 3- to 4-month intervals.
The most common complication of pulmonary RFA is pneumothorax, occurring in 59% of patients in a recent series. This is largely attributed to the size of the electrode used and is less frequent when positive pressure ventilation is avoided. Prolonged air leak (>5 days) occurred in 7% of patients. Other complications included hemoptysis requiring bronchoscopy, myocardial infarction, deep vein thrombosis, and respiratory failure, which occurred in 1% of patients. In addition, 3% of patients required subsequent drainage of pleural effusions. No intraoperative or in-hospital mortality was observed (Pennathur et al. Ann Thorac Surg. 2009[5];88:1601).
Local recurrence for stage I NSCLC after RFA was confirmed radiographically by CT scan, PET scan, or both after 31.5% of treatments (12/38). Two patients were successfully retreated for technical failures related to pneumothorax; three underwent radiotherapy with stable disease. Three patients died of metastatic disease; five died of pneumonia remote from treatment. The 2- and 4-year survivals were 78% and 47%, respectively. Median overall survival was 30 months. Tumors larger than 3 cm were more likely to recur locally (Pennathur et al. Ann Thorac Surg. 2009[5];88:1601).
CyberKnife® System
The rationale for SRS is based on the notion that higher doses of radiation improve local control and disease-related survival at the expense of increased toxicity in normal tissues (Sibley et al. Int J Radiat Oncol Biol Phys. 1998;40[1]:149). Initially described for the treatment of intracranial lesions, SRS utilized a rigid frame to immobilize a patient, stereotactically localize a lesion, and deliver a higher dose to a specific point with minimal dosing of surrounding normal tissue, using multiple convergent beams of radiation (Song et al. Oncology. 2004;18[11]:1419). As technology evolved, this technique was adapted for extracranial lesions. However, due to the presence of multiple critical structures in the thorax as well as the intrinsic movement of the lung, there was little interest in SRS for pulmonary lesions. Recent advances in SRS led to the development of CyberKnife, which overcame the limitations of conventional SRS in the thorax.
CyberKnife utilizes a frameless system in which the patient needs to not be immobilized. Instead, the CyberKnife System depends on tracking a tumor in real time and adjusting radiation beams accordingly, thus overcoming the limitations of respiratory movement and minimizing toxic exposure to nearby critical structures. It utilizes a 6-MV linear accelerator mounted on a robotic arm. Beams can be emitted in 12 directions from 110 arm positions. The CyberKnife System relies on internally placed radio-opaque fiducial markers that are implanted and allow tumor tracking based on internal rather than external reference points, thus eliminating the need for rigid immobilization (Pennathur et al. Ann Thorac Surg. 2007;83[5]:1820).
Indications for CyberKnife treatment are similar to those of RFA. Unlike those with RFA, patients with central nodules are also candidates for CyberKnife as there are no heat-sinking limitations.
There are no absolute contraindications to CyberKnife. Relative contraindications are similar to those of RFA. Multiple bulky nodules may be difficult to treat without surrounding radiation toxicity and may lead to treatment failure. Central lesions limit the total allowable dose.
The procedure for CyberKnife treatment begins with placement of one to four fiducials in and around the tumor. These are gold tumor markers that are 1 to 2 mm in size and allow for real-time tracking of the tumor. They are placed under image guidance, typically in an outpatient setting. Usually, a total of three fiducials (within, superior, and inferior to the tumor) will suffice. It is critical that the fiducials be placed within the lung parenchyma, as placement within the pleural space or in the fissures will allow migration, compromising tumor tracking.
A week after placement of fiducials, the patient is brought back for a contrast-enhanced CT scan of the chest and upper abdomen with 1.25-mm sections. The treatment plan is then jointly formulated by a thoracic surgeon and radiation oncologist. The tumor volume as well as a 0.5- to 1.0-cm margin of surrounding tissue is outlined using dosimetry software. The treatment area need not be spherical and in fact may be molded to encompass irregularly shaped nodules and to avoid neighboring critical structures. Precise doses at each point within and away from the planned treatment area may be calculated, thus avoiding reaching toxic thresholds in nearby critical structures.