Assessment of alternated cooling and heating treatment by US combined CEUS in the VX2 rabbit liver tumor model

Inoperable liver tumors are often treated by thermal ablation that destroys the tumor in situ and spares the adjacent hepatic tissue. Thermal-physical treatment has many advantages, but treatment by freezing or heating alone has some limitations. By taking the advantages and disadvantages of cryosurgery and thermotherapy into consideration, a new thermal technique that combines cryosurgery and radio frequency ablation has been proposed, thereby overcoming the disadvantages of each treatment strategy and improving therapeutic outcomes. This new approach remains to be systematically studied in the liver; therefore, this study was performed to estimate survival after alternated cooling and heating ablation therapy in a VX2 rabbit liver tumor model. Sixteen days after VX2 carcinoma implantation into the rabbit liver, tumors were treated with alternated cooling and heating ablation therapy. Rabbits were monitored for 6 months after treatment and assessed with ultrasound (US) and computed tomography at 1, 7, 14, and 30 days posttreatment. Untreated tumor-bearing animals served as the control group. Our results show that alternate freezing and heating ablation therapy resulted in a good recovery of VX2 rabbits. Compared with the control group, treated rabbits lived significantly longer (P < 0.05), with 70 % of treated animals surviving to 196 days posttreatment without metastasis or recurrence, while none of the controls did so. There was no local recurrence in the treatment group. All rabbits in the control group developed metastasis, while metastasis was only observed in 30 % of treated rabbits. These results suggest that alternate cooling and heating ablation therapy can prolong the survival time of rabbits with VX2 liver tumors and is an effective method for tumor therapy. Furthermore, we also showed in this model that contrast enhanced US is a valid follow-up approach to assess treatment effectiveness.