84: Nonoperative Treatments For Lung Cancer Percutaneous Thoracic Tumor Ablation

Introduction

Lung cancer remains the leading cause of cancer death for both men and women.¹ Only one-third of patients diagnosed with lung cancer are stage appropriate for surgical therapy. In addition, the rising population of elders in the United States and other Western countries has caused an increase in the number of patients with comorbidities, making primary surgical and curative therapy more complicated. In fact, a review of the California cancer registry revealed that stage I cancer patients who received no treatment have a median survival of 9 months. Eighty-nine percent of patients who were recommended for treatment but refused died within 5 years, and 78% of these patients died from cancer-specific causes. For T1 lesions, the survival rate for treated cancers was 155 months versus 26 months for untreated cancers.² For those patients treated with conventional external radiation alone, 5-year survival is 10% to 30%.³ Hence, appropriate treatment even for patients with major comorbidities should be available.

Surgical resection remains the gold standard treatment for early-stage lung cancer. In addition, the lung is a frequent site of metastasis in that pulmonary metastases occur in 30% of all malignancies.¹ However, a significant proportion of patients are unable or unwilling to undergo surgery. For these patients, ablative therapy may be an option for localized treatment. The technique of percutaneous tumor ablation has developed through the introduction of multiple modalities including microwave, cryoablation, high-intensity focused ultrasound scan, irreversible electroporation, interstitial laser, and radiofrequency ablation (RFA). The most studied and proven method among these is RFA.

Radiofrequency energy was first used in surgery with the application of cauterization in 1926, introduced by William T. Bovie, after pulsed electrical current was shown to cause coagulation in tissue, while continuous current resulted in cutting of tissue. The technique afforded precision cuts with minimal blood loss. Percutaneous RFA was first reported in 1990 for liver tumor ablation.⁴ Since then, the indications have expanded to other organs, such as kidney, bone, and lung. The mechanism of action and outcomes of treatment are reviewed.

Mechanism of Action

The term, radiofrequency ablation, refers to the therapeutic use of electromagnetic radiation (EMR) for the selective destruction and removal of biologic lesions. Electromagnetic radiation exhibits wave-like behavior corresponding in magnitude to the light spectrum (e.g., microwaves, radio waves, infrared, visible light, ultraviolet, X-rays, gamma rays). RFA uses energy at the frequency and length of radio waves (2–300 Hz).⁵ A circuit is created that flows from the tip of the electrode, to a large, diffuse grounding pad placed over the patient's thighs, to an external generator. The small cross-sectional area of the electrode creates a surrounding region of high energy flux. The molecules next to the electrode, usually water, align with the direction of the current. The rapidly alternating current causes the adjacent molecules to vibrate. Molecules farther away from the probe are affected ...