At the recent Society for Interventional Radiology (SIR) meeting held in Seattle, WA from March 1-6, a panel comprised of surgeons and interventional radiologists discussed the importance of image-guided therapy in the treatment and diagnosis of non-small cell lung cancer (NSCLC).
Moderated by Professor Kamran Ahrar, Professor of Radiology at the University of Texas MD Anderson Cancer Center, the session entitled 'Oncologic Intervention: Lung', provided delegates with a widespread overview about ablation techniques and technology, something that some of the audience members may not have had much experience with, according to Ahrar.
To begin, Dr Hiran Fernando, a thoracic surgeon from Boston Medical Center, Boston, discussed primary lung cancer, including the treatment options for different stages of lung cancer. According to Fernando, 175,000 people in the US are diagnosed with lung cancer each year, and there are 150,000 deaths from this disease each year in the US.
One of the primary reasons for this is that many patients will present with advanced disease so that curative therapy is not possible. Additionally many patients with early stage disease will not tolerate curative surgery because of other existing medical conditions
He then discussed the importance of identifying early stage tumours and continued to explain treatment options for NSCLC, according to the stage characterisations of the cancer (eg. Stage 1a characterisation involves tumours that are 3cm or less and are usually treated with resection as a stand alone therapy, Stage1b involves tumours greater than 3cm and are usually treated either with surgery alone, or in combination with chemotherapy).
"With Stage 1 cancer, there is a 70-80% chance of survival at five years," said Fernando. "Combination therapy for Stage II and III NSCLC is the best treatment option, which includes surgery plus adjuvant chemotherapy for stage II and neoadjuvant chemotherpaytherapy, followed by surgery for stage III. For Stage 1 NSCLC, lobectomy is the current preferred choice. Sublobar resection is preferred for moderate risk patients, and external beam radiation is the current standard for high risk patients, however radiofrequency (RF) ablation is probably better than external beam radiation," he concluded.
Devices and techniques
Following Fernando, Christopher L Brace, assistant scientist in the Department of Radiology at the University Wisconsin in Madison, discussed the current RF devices in operation today. He also discussed other potential sources of energy, such as cryoablation and microwave energy.
In discussing the technology, Brace identified the RITA Model 1500/Starbust as suitable for large ablations, however he explained that in his opinion placement can be problematic with this model. The Boston Scientific RF 3000/LeVeen is a 13-gauge applicator and according to Brace, is also suitable for large ablations, but again, placement can be problematic and electrodes are not independent. And finally, the Celon device (Celon Medical Instruments) contains bipolar, 16-gauge electrodes with saline infusion, but the bipolar electrodes may limit the ablation margin, which could potentially be problematic.
After identifying the ablation devices currently used, Brace then discussed how RF can be used in the lung, but explained that there are current limitations with this technique such as:
High tissue impedance reduces power
Low thermal conductivity limits heating
Perfusion and air flow = heat sinks (bronchial occlusion)
Saline infusion according to Brace enhances RF, but with hypertonic saline there are safety issues that need to be considered.
In regard to microwave ablation, Brace said that this technique is not largely available, but is effective, fast heating, unaffected by aerated tissue, has multiple applicators and large-diameter antennas (needed for high powers), and therefore is advantageous over RF.
According to Brace, cryoablation has the potential to effectively treat lung cancer by freezing tissue and causing necrosis, however it will be several years before this technique will be widely available.
To conclude, Brace explained that "RF ablation technology can be used effectively in the lung, and additional strategies such as saline infusion and bronchial occlusion can enhance results, however hypertonic saline has a questionable safety record. New technologies that can overcome the limitations of RF, include microwave ablation and cryoablation."
RF ablation: Treating Stage 1 NSCLC
Riccardo Lencioni, associate professor of Radiology at the University of Pisa, Italy, presented data from clinical trials and his own research to discuss the results of RF ablation therapy in treating Stage 1 NSCLC.
He explained that for these types of tumours, generally, surgical resection is the first line of treatment, with an overall survival rate of 60-70% at five years. In comparison, radiation therapy as a treatment option for NSCLC has a 10-20% overall survival rate at five years. Somewhere in between these two procedures lies RF ablation, in which Lencioni continued to discuss by outlining that combining RF ablation and radiation therapy could lead to a 30-45% overall survival rate at five years, which is obviously a better outcome than just radiation therapy alone.
Investigating data published on RF ablation and NSCLC, Lencioni pointed out that there are just eight studies on lung ablation, out of these eight, four studies have been conducted on RF ablation as a stand alone option, and just two on RF ablation with radiation.
Citing data from the RAPTURE (Radiofrequency Ablation of Pulmonary Tumors Response Evaluation) trial, a prospective, multi-centre study involving 106 patients, Lencioni, presented two-year survival outcomes from this lung RF ablation clinical study in which 186 lung tumours were treated.
All 106 patients enrolled in the trial, were non-surgical candidates with 33 presenting with primary NSCLC, 53 presenting with colorectal cancer (CRC) metastases, and 20 presenting with metastases from other primary malignancies. Complete ablation of macroscopic tumour as evidenced at three-month CT was achieved in 173 of 186 tumours.
The results showed that overall survival was 69% at one year and 49% at two years in patients with NSCLC; and 86% at one year and 62% at two years in patients with CRC metastases. Cancer-specific survival was 91% at one year and 91% at two years in patients with NSCLC; and 88% at one year and 72% at two years in patients with CRC metastases.
Lencioni also cited results from the Dupuy study, which involved patients with Stage 1 NSCLC, in which RF ablation was the stand alone treatment. At five years, overall survival was 38%.
In conclusion, Lencioni explained that, "RF ablation yields high local tumour control rates in patients with Stage 1 NSCLC, and is associated with acceptable morbidity. Overall and cancer-specific survival outcomes support the use of RF ablation of combined RF ablation and radiation therapy for medically inoperable patients.
"Further investigation, through RCTs, is needed to establish the role of RFA with respect to chemo/radiation therapy protocols in NSCLC management," he added.
Patient selection
The final speaker, Dr Robert Suh, associate clinical professor of Radiology at the University of California at Los Angeles Medical Center, discussed technical aspects of ablation, such as selecting patients, how procedures are performed and how to follow-up with the patient.
He explained that RF ablation lesion selection criteria involves a number of considerations, such as:
Number: Solitary Multiple -<5 in number
Size: Smaller is better
Shape: Spherical better
Location: Non-continuous with vital structures is better
Texture: Avoid 'push back' effect, when the tumour pushes away making it difficult to penetrate
Technical RF ablation considerations to take into account, include:
RF energy related:
Fever and malaise - 'Post-ablation syndrome'
Dispersive electrode burns
Medical device interference-pacers, PICDs, etc
Conscious sedation related:
Nausea/vomiting
Aspiration/ARDS
Arrhythmias
Radiation related
Tumour Necrosis Syndrome
Following this, Suh stressed the importance of imaging follow-up. "Reliable imaging is essential for proper RF ablation," he said. "Knowledge of ablation zone computerised tomography (CT) appearances is critical for early identification of tumour recurrence. Contrast-enhanced computed tomography (CECT) and Positron emission tomography (PET) should be used in conjunction, and diligent and rigorous follow-up is required."
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