Abstract:

Background and purpose: Surgical resection, radiotherapy and chemotherapy are main remedies for malignant lung tumors. However, to explore new therapies for patients ineligible for surgery, multiple metastases in lung and progressive with radiotherapy or chemotherapy is an urgent problem. Recently, radiofrequency ablation has attracted a wide spread attention as a new treatment for malignant lung tumors. In this study, we investigated CT-guided radiofrequency ablation of VX2 lung tumor in rabbits, with the aim to observe CT images and pathologic regression, to evaluate efficacy and to explore treatment parameters of RFA. Methods: Build the model of VX2 lung tumors in rabbits with a new method of CT-guided percutaneous puncture by coaxial trocar. The experimental group included 27 rabbits with RFA treatment, while the control group had 9 rabbits with false treatment. Two groups were performed CT scans at different time points to observe CT images. For the experimental group, 18 were killed at different time points to observe pathologic regression; while the rest was kept natural death, evaluating efficacy and calculated survival time. The control group had natural death and the survival time was calculated. Results: CT images taken immediately after RFA showed the lung tumor surrounded by ground-glass opacity (GGO), sometimes, with a cavity or small vacuoles in the lesion. It couldn’t exclude the residual of tumor cells even without enhancement of CT scan according to pathological finding in the follow-up. Twenty-four hours after operation, in gross anatomy, the area of RFA showed four zones from inside to outside along power gradient: the carbonization or evaporation center, gray coagulation necrosis zone, red-brown hemorrhage zone and pink hyperemic exudate zone. There was some degree of inflammation pathologically around the lesion after operation, which was absorbed within four weeks mainly; eventually, left thickwalled fibrous tissue encysting coagulation necrosis and slightly remote hemorrhage. The rate of complete response of the experimental group was 78%. The survival time of the experimental group and the control group had significant difference (t=2.634, P=0.018), which was 38.0±5.9 d and 24.0±3.1 d, respectively. The linear regression equation between RF energy and the lesion size was Y^=-2.3372+1.4361X, with test of regression coefficient (P=0.000). Conclusion: The method of CT-guided percutaneous puncture by coaxial trocar to build the model of VX2 lung tumors in rabbits was safe and rapid, with high tumor formation rate. Our study showed not only safety, micro-invasion and low rate of complications but also definite efficacy of RFA for lung tumors. To evaluate efficacy, 1 month after operation could be the new baseline due to the development and succession of the RFA area. There was relationship of linear regression between RF energy and the lesion size.

Key words: VX2, Lung tumor, Computer tomography (CT), Radiofrequency ablation (RFA), Pathologic regression