Radio frequency ablation of renal cell carcinomas using MR-guidance: initial results

Purpose: First results of a study about the efficacy of magnetic resonance-(MR-)guided radiofrequency ablation of renal cell carcinomas (RCC) are presented. Material and Methods: Eight patients (63 to 82 years old) with RCC up to 3.9 cm in diameter were treated by percutaneous RF ablation under MR-guidance in an open MR scanner at 0.2T field strength. For positioning of the RF-electrode, fluoroscopic rapid gradient echo sequences (acquisition time about 2 sec) were used. The ablation was monitored by intermittent imaging with T1- and T2-weighted spin echo sequences. Results: In each patient, the applicator was successfully positioned within the tumor using MR-guidance. Seven of eight patients were completely treated within one single session; one patient had to be retreated for tumor relapse at 13 months. The mean number of electrode repositionings under MR guidance for complete ablation was 2.0; ablation time ranged between 12 and 28 minutes. Maximum diameter (volume) of induced coagulation necrosis within one session was 3.9 cm (30.2 cm(3)) by using cluster electrodes. With single electrodes, maximum short axis diameter of coagulation without repositioning was 2.4 cm (11.6 cm(3)). All patients are now disease-free after a mean follow up of 13 months (5 to 21 months). No major complications occurred during or after the ablation procedure. Conclusion: MR-guided RF ablation in an open interventional 0.2T MR-unit is a safe and effective modality for the treatment of RCC. Fast MR-imaging is a convenient method for exact positioning of MR-compatible RF-electrodes. Near on-line MR-monitoring of ablation procedure with T2-weighted imaging allows for immediate assessment of the coagulation extent.