Abstract
This study aims to examine, for the first time, the introduction of cationic polymer solutions to improve radiofrequency ablation (RFA) in terms of a potentially enlarged ablation zone. By using in vivo and computational RFA studies, two cationic polymers, Chitooligosaccharides (COS) and carboxymethyl chitosan (CMC), diluted in deionized water, were injected into tissues separately surrounding the RF bipolar electrode prior to power application. A total of 9 rabbits were used to 1) measure the increase in electrical conductivity of tissues injected with the cationic polymer solutions, and 2) explore the enhancement of the ablation performance in RFA trials. A computer model of RFA comprising a model of the solution diffusion with an RF thermal ablation model was also built, validated by the in vivo experiment, to quantitatively study the effect of cationic polymer solutions on ablation performances. Compared to the control group, the electrical conductivity of rabbit liver tissues was increased by 42.20% (0.282 ± 0.006 vs. 0.401 ± 0.048S/m, P = 0.001) and 43.97% (0.282 ± 0.006 vs. 0.406 ± 0.042S/m, P = 0.001) by injecting the COS and CMC solution at the concentration of 100 mg/mL into the tissues, denoted COSDW100 and CMCDW100, respectively. Consequently, the in vivo experiments show that the ablation zone was enlarged by 95% (47.6 ± 6.3 vs. 92.6 ± 11.5 mm2, P < 0.001) and 87% (47.6± 6.3 vs. 88.8 ± 9.6 mm2, P < 0.001) by COSDW100 and CMCDW100, respectively. The computer simulation shows that the ablation zone was enlarged by 71% (51.9 vs. 88.7 mm2) and 63% (51.9 vs. 84.7 mm2) by COSDW100 and CMCDW100, respectively. The injection of the cationic solution can greatly improve the performance of RFA treatment in terms of enlarging the ablation zone, which is due to the increase in the electrical conductivity of liver tissues surrounding the RF electrode. This study contributes to the improvement of RFA in the treatment of large tumors.
Highlights
R ADIOFREQUENCY ablation (RFA) as a thermal ablation therapy is extensively used to treat primary and secondary malignancies in clinical practice [1], [2]
The ablation time was increased from 77 ± 17 s to 300 ± 104 s and 275 ± 73 s because of the introduction of COSDW100 and CMCDW100, respectively
The end result was that the injection of COSDW100 and CMCDW100 led to a 95% increase in the size of the ablation zone (47.6 ± 6.3 vs. 92.6 ± 11.5 mm2, P < 0.001) and 87% (47.6 ± 6.3 vs. 88.8 ± 9.6 mm2, P < 0.001), respectively, but there was no significant difference between the cationic solution groups (P = 1) (Fig. 9d)
Summary
R ADIOFREQUENCY ablation (RFA) as a thermal ablation therapy is extensively used to treat primary and secondary malignancies in clinical practice [1], [2]. The RFA systems currently used in clinical practice are designed such that the delivery of RF power is halted when an abrupt increase in impedance has been detected, a phenomenon known as “roll off” [4], [5]. Roll-off due to increased impedance is one of the main reasons for the incomplete ablation of large tumors treated by RFA. Such phenomenon has motivated several efforts in various areas to get around this “roll off” problem, ranging from RF electrode design to target tissue property modification. The cool-tip electrode is used to cool tissue temperature around the electrode, which has the effect of delaying tissue charring in clinical practice [6]. Other authors have demonstrated that the injection of normal saline solution or diluted hydrochloric acid (HCl) can efficiently delay roll-off
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