Radiology: PET/CT effective for lung RF ablation follow-up

Axial fused image (SUVmax, 2.2) after RF ablation at FDG PET/CT. Image source: Deandreis et al. Radiology 2011; 258:270-276.

Integrating FDG PET/CT imaging into radiofrequency (RF) ablation treatment planning and follow-up improved patient care by depicting unknown tumors prior to treatment and facilitating early diagnosis of incomplete treatment post-treatment, according to a study published in the January issue of Radiology. The study also demonstrated a complete treatment rate of nearly 90 percent with lung RF ablation.

Although few studies have documented the utility of RF ablation in unresectable lung lesions, recent research suggests it is a safe and minimally invasive therapy, offered lead author Desiree Deandreis, MD, from the departments of nuclear medicine and endocrine oncology at Institute Gustave Roussy and University of Paris, and colleagues. However, physicians require a reliable means to assess treatment response and early relapse.

The researchers recruited 34 consecutive patients (mean age, 64.4 years) for a prospective study to compare FDG PET/CT and chest CT in the evaluation of the effectiveness of lung RF ablation with the treatment failure rate as the end point.

Each patient underwent chest and abdominal CT and FDG PET/CT staging exams prior to ablation. Follow-up PET/CT studies occurred at 24 hours, one month and three months after ablation for patients whose scans showed FDG uptake in target lesions. Follow-up chest CT studies were performed at one and three months post-ablation. Median follow-up was 15 months. Experts judged post-ablation PET/CT and CT studies as depicting complete response, persistent tumoral disease or equivocal finding.

Deandreis and colleagues reported that pre-treatment PET/CT depicted 15 previously unknown tumor sites in 11 patients, which led to treatment changes in nine patients. The final study population included 28 patients who were treated and followed up.

The study indicated the effectiveness of RF ablation as physicians diagnosed incomplete treatment in fourteen percent of patients within three months and treatment failure in the three patients at one month and one patient at three months after ablation.

PET/CT revealed complete treatment in 19 of 28 patients. Of the remaining patients, PET/CT findings were used as the basis for a diagnosis of incomplete treatment in five patients, with four confirmed as true-positive and one as false-positive. Uncertain findings were present in four patients at one month; all were later confirmed as inflammatory.

Chest CT imaging led to the diagnosis of complete treatment in 93 percent of patients within three months of ablation. However, three of these 26 cases were false-negative; PET/CT had assessed the three false-negatives as incomplete treatment. CT diagnosed incomplete treatment in two patients with one case true-positive and one false-positive. The false-positive was also false-positive on PET/CT imaging.

“Our results demonstrate that FDG PET/CT depicts a higher number of treatment failures than chest CT, without any cases of false-negative findings,” offered Deandreis and colleagues. PET showed incomplete treatment as early as one month after RF ablation, which was not depicted on chest CT, continued the researchers.

“FDG PET/CT was also efficient in the detection of late relapse, suggesting its possible role in a systematic long-term follow-up after treatment,” offered Deandreis, who added that further studies are needed to confirm the superiority of PET/CT over chest CT in the evaluation of the effectiveness of lung RF ablation.