In Argentina, lung cancer is the third most common cancer, accounting for 9.3% of all malignancies¹. In addition, the lung is a common site of metastasis, mainly of breast, colon, prostate, kidney and bladder cancers. Historically, surgical resection has been the standard of care with the best long-term survival rate. However, several previous studies have demonstrated the safety and efficacy of radiofrequency ablation (RFA) for both primary and secondary tumors. Even in these studies, overall 2-year survival after propensity score matching was similar to that of patients undergoing surgery and stereotactic body radiation therapy (SBRT)².

In our hospital, all patients with lung tumors are discussed in a multidisciplinary conference made up of oncologists, thoracic surgeons, specialists in diagnostic imaging, radiotherapists and interventional radiologists to decide the therapeutic approach for each particular patient. Radiofrequency ablation is suggested when the indications of the Clinical Practice Guidelines in Oncology (NCCN Guidelines^®) are fulfilled: patients with stage IA non-small cell lung cancer (NSCLC) and high surgical risk, those with multiple lung lesions (metastases from colorectal, lung or renal carcinoma, melanoma, hepatocellular carcinoma and sarcoma) or with locoregional recurrence. We consider patients with one major criterion or two minor criteria or greater to be at high surgical risk. Major criteria include FEV1 or DLCO ≤ 50% and minor criteria include FEV1 or DLCO 51-60%, age ≥ 75 years, pulmonary hypertension, FEV1 ≤ 40%, resting or exercise arterial PO2 < 55 mm Hg, and PCO2 > 45 mm Hg.

Once RFA has been indicated, a computed tomography (CT) scan of the chest should be performed to evaluate tumor size and its relationship with the parietal pleura, vascular structures, bronchi and pulmonary fissures. With this information we will be able to choose the appropriate length of the electrode, number of electrodes and length of the active tip. We also perform a preoperative risk assessment which includes coagulation tests, electrocardiogram and evaluation by a cardiologist, pulmonologist and anesthesiologist to detect those patients with contraindications for the procedure. The absolute contraindication criteria we use are severe emphysematous disease with bullae, life expectancy < 3 months, ECOG (Eastern Cooperative Oncology Group) score > 2, non-correctable bleeding diathesis and small-cell lung cancer. Relative contraindications are tumors located near large vessels or pulmonary hilum (< 1 cm), cardiac pacemaker, correctable bleeding diathesis and impaired lung function. As the European Society of Interventional and Cardiovascular Radiology (CIRSE) considers pulmonary ablation a procedure with high bleeding risk, coagulation parameters should be checked, and the necessary corrections should be made before the procedure.

The procedure is performed under sedation, so that the patient can cooperate with breathing instructions. General anesthesia also increases pneumothorax risk when positive pressure is used; nevertheless, we use it in pediatric patients and in those who cannot tolerate prolonged supine position, prioritizing their safety. The position is chosen based on tumor location and access site. We perform a CT scan of the thorax to obtain an initial image of the thorax and locate the lesions to treat. Once the tumor has been identified, a radiopaque mark is placed on the tumor projection on the skin surface, the percutaneous access is planned on the monitor and the skin is marked (Fig. 1). After antisepsis, sterile drapes are placed on the puncture site and local anesthesia with lidocaine 1% is administered at the level of the subcutaneous tissue and pleura. A scalpel is used to create a 1-2 mm skin incision and the electrode is introduced and positioned along the longitudinal axis of the tumor to achieve an adequate oncologic margin (10 mm) (Fig. 2 and 3). This may involve using the longest pathway to the lesion to properly anchor it in the lung parenchyma. The electrode may pass through the tumor (single electrode) or its edges (multiple electrodes) and must be at least 10 mm larger than the tumor’s maximum diameter to achieve an adequate ablation halo (Fig. 4). The temperature and impedance used will depend on the manufacturer’s specifications.

When the tumor is close to structures that must be preserved, thermoprotection techniques can be used, as iatrogenic pneumothorax (Fig. 5) and hydrodissection. A CT scan must be performed immediately after the procedure to evaluate the margin of the tumor ablated and rule out possible severe complications. The most common complications after RFA are pneumothorax (11-52%) and parenchymal hemorrhage (6-18%), although they are usually asymptomatic and do not require an additional procedure. Patients with mild asymptomatic pneumothorax require expectant management.

Severe, symptomatic or recurrent pneumothorax is managed with placement of a Heimlich valve. Pleural effusion is usually a reactive phenomenon but should be monitored to rule out bleeding events. Hemothorax is extremely uncommon, and is self-limited in most cases; however, arterial bleeding may require endovascular embolization. Other rare complications include bronchopulmonary fistula, pneumonia and gas embolism³. The patient remains hospitalized for 24 hours for close monitoring and a CT scan is performed 1 h after the procedure. Additional CT scan monitoring is scheduled at 1, 3, 5, 9, 18 and 24 months and once a year thereafter. Although CT scan is the standard for imaging care, positron emission tomography (PET-CT) has gained relevance. In our center, we indicate a PET-CT scan at 3 and 12 months after the procedure and when recurrence is suspected (Fig. 6). CT monitoring should be performed by professionals completely aware of the expected changes occurring in the different phases: after-treatment-phase (< 24 h), early-phase (< 24 h to 1 month), intermediate-phase (1 to 3 months), and late phase (> 3 months) after pulmonary ablation.

Many studies have shown encouraging results of RFA in patients with stage I NSCLC. The first prospective study evaluated 54 stage IA patients who underwent RFA and reported an overall survival of 86.3% at one year and 69.8% at two years, reaching 83% in tumors < 2 cm⁴. Another prospective study included inoperable patients with stage IA NSCLC and tumors ≤ 3 cm and reported overall survival of 91.67% and 58.33% at 1 and 3 years, respectively⁵. Careful patient selection and appropriate knowledge of the technique are of utmost importance to achieve these survival rates. Therefore, it is necessary to know that tumors with a diameter between 2 and 3 cm have higher success rate and lower risk of recurrence. The most important retrospective series on SBRT found that the overall survival obtained with RFA (85.4%, 65.2%, 47.8% and 24.6% at 1, 2, 3 and 5 years, respectively) was not inferior to that obtained with SBRT (86.3%, 64.5%, 45.9% and 26.1% at 1, 2, 3 and 5 years, respectively)⁶. Therefore, treatment choice should be based on each individual patient in agreement with the different specialties.

Another indication for RFA is local recurrence after radiation therapy. Cheng et al. demonstrated median overall survival of 35 months and recurrencefree survival of 14 months⁷. Minimally invasive treatments have gained prominence with the advent of immunotherapy. It has previously been shown that local treatments increase the immune system response and that the effect obtained by combining them is greater than when they are used individually⁸. At present, several ongoing clinical studies are being conducted to evaluate the synergy between immunotherapy and thermal ablation. Oligometastatic disease can also be treated with radiofrequency as it was demonstrated in the prospective RAPTURE study, which reported an overall survival of 89-92% and 64-66% at 1 and 2 years, respectively⁹. Similarly, a recent study evaluated the efficacy of radiofrequency in patients with colorectal lung metastases < 3 cm and found an overall 3-year survival of 84% and a complication rate of 1%¹⁰. As in NSCLC, metastases < 3 cm have better response and longer survival. Other prognostic factors in oligometastatic disease are primary tumor origin, disease-free interval and > 3 lung metastases¹¹. Our experience includes 12 lung ablations in 9 patients between 2017 and 2022. Mean age was 62.33 (35-83) years and 55% (5 patients) were women. Of the 12 lung ablations, 58% (7 patients) were due to metastatic disease and 42% (5 patients) to NSCLC. The mean tumor diameter was 2 (1-3.3) cm. Overall morbidity was 42% (5 complications). Three patients (25%) presented pneumothorax, and only one of these patients required placement of a Heimlich valve. In addition, 1 patient developed parenchymal hemorrhage and there was one case of pleural effusion; both were self-limited.

As a conclusion, radiofrequency ablation is a minimally invasive technique resulting in overall survival rates similar to those achieved with surgery in selected patients with early-stage NSCLC, local recurrence and oligometastatic disease who are not eligible for surgery.