New imaging techniques aid ablation strategies

December 28, 2005

New imaging techniques and methods spotlighted in December at a special Interventional Oncology Symposium can help reduce the rate of recurring tumors, find disease that was missed in the first phase of treatment, and make ablation more practical.

New imaging techniques and methods spotlighted in December at a special Interventional Oncology Symposium can help reduce the rate of recurring tumors, find disease that was missed in the first phase of treatment, and make ablation more practical.

Some of the most notable presentations at the symposium, jointly sponsored by RSNA and the Society of Interventional Radiology Foundation, covered intraprocedural imaging, the role of PET and MR in follow-up imaging, and a promising new method for using angiographic CT to image ablation techniques.

INTRAPROCEDURAL CT HELPS ELIMINATE RECURRENT KIDNEY TUMORS

Intraprocedural contrast-enhanced CT helped reduce the rate of incompletely treated renal cell carcinoma lesions by approximately 64 %, according to a study presented by Dr. Kyle A. Krehbiel of Wake Forest University.

The retrospective study of 90 tumors in 82 patients with stage 1 and 2 renal cell carcinoma divided patients into two groups. Patients with creatinine levels of 2 or less underwent a contrast CT study after the tumor was presumed to be fully ablated. Patients with a creatinine level higher than 2 were not scanned, and the ablation endpoint was determined by the estimated ablation zone.

The intraprocedural scans found residual tumors in 10% of patients, Krehbiel said. The team used contrast CT to target the residual tumor and immediately reablated the area.

After an average follow-up of 10 months, the team discovered recurrent disease in 5.8% of patients who had undergone intraprocedural contrast CT. By contract, 19% of the patients who had not undergone intraprocedural contrast CT had recurrent disease.

On follow-up, the team discovered that none of the residual tumors that had required additional ablation had recurred. However, 6.4% of tumors that did not enhance with contrast CT showed recurrent disease on follow-up imaging, indicating that the scans may miss microscopic viable tumor cells.

The size of the lesion seemed to influence the rate of recurrence. The average size of lesions in either group that showed residual or recurrent tumor was 4.3 cm, while lesions that did not show residual or recurrent tumor averaged 2.5 cm.

PET/CT PRE-AND POSTPROCEDURAL IMAGING

Two studies evaluated the effectiveness of PET in evaluating the potential effectiveness of RFA before a procedure and in searching for residual tumors after RFA.

PET/CT is a valuable tool to confirm the indication, to plan, and to control the success of interventional tumor therapy in the liver, according to a study presented by Dr. Peter Herzog of the University of Munich. PET tends to find smaller tumors that are not yet visualized in CT.

A PET/CT scan before interventional therapy of liver tumors confirmed the indication for interventional therapy in 48 out of 62 patients. Fourteen patients did not undergo interventional treatment because of extrahepatic metastatic disease or local recurrence. In four of the 14 patients, extrahepatic disease was evident only on the PET scan, while two extrahepatic manifestations were evident only on the CT scan.

PET proved useful for discovering hepatic recurrences. Eighteen patients who underwent interventional therapy developed either local recurrence at a treated lesion or new metastatic disease within the liver. CT missed five of the recurrences in the first control, while all of the recurrences were discovered by PET.

A study presented by Dr. Hilmar Kuehl of University Hospital Essen found that PET/CT is more accurate than CT or MRI for finding residual tumor in the liver after RFA.

Of 16 patients with 24 hepatic malignancies, eight patients with 15 PET-positive liver lesions were included in the study. Postinterventional PET/CT was performed 24 hours after ablation and repeated after one, three, and six months, then every six months thereafter. MRI was done at the same dates after PET/CT.

Seven of 15 lesions showed local tumor recurrence under follow-up. All recurrences were identified by PET/CT, whereas CT missed four cases and MRI showed recurrent tumor in five cases. The accuracy for tumor detection for CT alone was 84 % and for PET/CT, 90%. The accuracy of MRI was 88%.

Very small areas of residual tumor may be missed with morphologic imaging and with PET/CT, Kuehl said.

IMAGE-GUIDED CHEMOEMBOLIZATION WITH AN ANGIOGRAPHY SYSTEM

Frank Wacker of the radiology department at Charité-Campus Benjamin Franklin in Berlin presented early results from an evaluation of the feasibility of rotational angiography during liver chemoembolization. He found that the system was very fast, but that multiple artifacts may hamper the diagnostic value.

Seven patients with liver tumors underwent chemoembolization procedures performed on a floor-mounted angiographic C-arm system equipped with a flat detector. To generate CT-like images, the C-arm rotates around the liver and 240 to 480 acquisitions are performed in 10 seconds. Immediately after image reconstruction on a separate workstation, CT-like images were available in the angio suite.

Wacker found that rotational angiographic images could be obtained in all patients. With an experienced operator at the workstation, the images were available in the angio suite well within 10 minutes. The interventionalist rated the image quality sufficient for decision-making in five patients with an actual therapeutic impact in three. In comparison with MSCT, the image quality was worse in all cases. In two patients, images were not diagnostic.

Although these results are early and more study is needed, Wacker said the preliminary findings suggest that angiographic systems can bring slice imaging into the interventional suite. Although the system has not yet been tested with RFA, Wacker plans to use it with the modality in the future.