Radiology: Thermal ablation of lung tumors comes of age
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| Post-cryoablation cardiac-gated gadolinium-enhanced T1-weighted axial MRI shows large area of nonenhancement, consistent with tumor necrosis. Source: Radiology. |
“It is clear that patients who have lung malignancies with limited treatment options are benefitting from image-guided ablation therapy,” wrote Damian E. Dupuy, MD, from the department of diagnostic imaging, Warren Alpert School of Medicine of Brown University in Providence, R.I.
Dupuy referred to a 13 percent increase in the use of lung radiofrequency ablation from 2007 to 2008 based on data from Medicare Current Procedural Terminology codes. And while clinical studies are limited, existing data indicate an overall survival rate of 48 to 80 percent at two years.
According to Dupuy, 15 percent of all lung cancer patients and 30 percent of patients ages 75 years or older with a diagnosis of stage I or II non-small cell lung cancer are not considered surgical candidates. Other clinical factors changing the lung cancer treatment landscape include the increasing detection of smaller cancers via CT screening and advances in tumor characterization by means of genomic and proteomic analysis. These trends could portend an increase in utilization of thermal ablation.
“Image-guided thermal ablation offers clinicians and patients a repeatable, effective, low-cost and safe treatment for effective palliation and, in some cases, cure of both primary and metastatic thoracic malignancies either before or concurrently with systemic therapy and [radiation therapy],” wrote Dupuy.
Dupuy reviewed various thermal ablation techniques, which include:
- Radiofrequency (RF) ablation: The most widely used technique, RF ablation applies electromagnetic energy into the tumor via image guidance, heating and killing the tissue.
- Microwave ablation: Like RF ablation, microwave ablation uses electromagnetic waves to heat tissue. It delivers a larger zone of heating and may provide a greater convection profile in the lung, reduce local recurrences and allow faster treatment. Multiple applicators can be used to treat large tumors.
- Cryoablation: Used in liver tumors for more than 30 years, cryoablation applies liquid nitrogen to the tumor. Using CT or MR guidance, physicians can compare the target with margins to achieve greater confidence and reduce the margin. Multiple applicators can be used.
- Laser ablation: A thermal technique that converts light energy into heat, laser ablation can be applied to a limited zone via CT guidance. The technique has not yet been applied to lung tumors in the U.S.
Two patient groups are candidates for ablation, explained Dupuy. The first includes non-surgical candidates with an intention to achieve definitive therapy. Such patients have comorbidities or contraindications to surgery and a finite number of biologically favorable metastases. In the second group, thermal ablation can be used for palliation.
Dupuy noted that most studies of thermal ablation in lung cancer patients are single-site case series. One National Cancer Institute prospective trial examining two-year survival and local control is under way at 25 institutions. Results will be available in 2012.
In practice, long-term imaging surveillance of the ablated region is required, wrote Dupuy. This can be achieved by CT, MR or FDG PET.
Ablation is associated with several potential complications, noted Dupuy. These include mild to moderate pain, pneumothorax in 10 to 35 percent of patients and pulmonary complication such as pneumonia.
Dupuy concluded with a call for additional studies, including prospective comparison of various ablative techniques with other treatments and urged radiologists to learn more about the technology and burgeoning field.