Feasibility of MR-guided focused ultrasound with real-time temperature mapping and continuous sonication for ablation of VX2 carcinoma in rabbit thigh

The efficiency of MRI-guided focused ultrasound (FUS) hyperthermia with continuous sonication was investigated for the treatment of VX2 carcinoma implanted in rabbit thigh muscle. Six rabbits were treated with a single session of FUS when the tumor diameter exceeded 2 cm (10-21 days after implant). The FUS treatment method was based on a spiral trajectory of the focal point that allows continuous sonication under automatic, real-time MR guidance. The total heating time was approximately 1000 sec. Efficacy of treatment was evaluated twice a week based on clinical (weight) and MRI data. Treated animals were sacrificed 5 weeks after the heating procedure and histological analysis was performed. Tumor regression was observed in each treated animal. Complete ablation of tumor, with confirmation by histological analysis, was obtained in five of six treated cases. Tumor regrowth occurred in one animal. Thermal injury was limited to the targeted region in three cases, but ablation also reached some healthy muscle around the tumor in the other three cases. A good correlation was found between postmortem histological analysis and premortern MRI data. Efficacy of MR-controlled hyperthermia using FUS heating with spiral trajectories was demonstrated for successful local control of intramuscular VX2 tumor.