# Feasibility of a Drug-Releasing Radiofrequency Ablation System in a Porcine Liver Model
## 4 Discussion  
This study using DRCWE was able to perform ablations and successfully delivered the drug in the ablation zone margin. The results of the experiment demonstrated that the coagulation zone using DRCWE could be created with the mean diameter (Dmax, 3.56 \(\pm\) 0.19; Dmin, 2.56 \(\pm\) 0.27) and AV of 15.22 \(\pm\) 2.30 cm\({}^{3}\), which seems to be within the range of those of other studies [18; 19]. Furthermore, circularity > 0.70 could indicate that the ablated lesions were circular. Additionally, the IV was considerably higher than the AV (17.21 \(\pm\) 2.85 vs. 15.22 \(\pm\) 2.30 cm\({}^{3}\)) with statistically significant differences. This suggested that the released drug could effectively prevent local recurrence around the ablated lesions. In addition, the SUV as a simple image-based measure, which is widely used in clinical practice, was used to remove variability introduced by differences in animal size and the amount of injected FDG [20; 21]. The mean SUV was 0.44 \(\pm\) 0.05, which means that 40% of the drug has been released to the surroundings. Thus, adjusting the amount of the drug to take this into account would be better. Considering that creating at least a 5-mm safety zone around the tumor is necessary to decrease local recurrence after RFA for primary and secondary liver malignancies, the results of this study indicate that DRCWE can successfully treat a 3.5-cm-diameter tumor without creating an overlapping ablation. Therefore, DRCWE may not only be a successful treatment for HCC but may also lower the recurrence rate by releasing the anticancer drug to residual cancer cells after RFA. FDG-PET sensitivity for detecting HCC is approximately 50-70% [22]. Although the exact sensitivity was unknown because the normal liver model was used in this experiment, a similar retention rate was measured, which was 72.89% \(\pm\) 4.22% (range, 66.35-76.97%). Here, high retention rates of >70% on average may be seen as evidence that the DRCWE RFA system can be useful. Figure 5: \({}^{18}\)F-fluorodeoxyglucose (\({}^{18}\)F-FDG)-positron emission tomography/magnetic resonance imaging examination imaging in the extracted liver. (**a**) Sagittal sections of the extracted liver. (**b**) The focal \({}^{18}\)F-FDG uptake on transverse cut sections was calculated by drawing the regions of interest. Local tumor recurrence is defined as the reappearance of enhancing tissue within and around the ablation zone, which is secondary to the presence of residual viable or unablated tumor in patients previously considered to have complete ablation. The reported local recurrence rates after RFA ranged from 2% to 60% and have been currently managed by hepatic resection, salvage liver transplantation, and repeated RFA [23; 24]. However, retreatment for local recurrence is often difficult and has a high failure risk [25; 26]. A recent impact study reported the use of chemotherapy and bevacizumab with or without RFA for the treatment of unresectable liver metastases in patients with colorectal cancer [27]. Therefore, it is believed that DRCWE may reduce the local tumor recurrence rate after RFA by utilizing the chemotherapeutic agents in patients with HCC and may also increase the RFA indications to include larger liver malignancies. A tendency to leave viable tumor cells in the margins or clefts of overlapping ablation zones for large tumors was noted (i.e., >3 cm diameter) although RFA is more effective for small-sized tumors (i.e., <3 cm diameter) [28; 29; 30]. Therefore, the ablation of larger liver tumors increases the possibility of incomplete ablation or local recurrence. The local failure rate of these tumors was high at the site of the primary tumor as well as elsewhere within the liver at sites remote from the treatment location due to vascular spread [30]. In this situation, multiple overlapping treatments with either a single electrode or multiple electrodes to increase the ablation zone size were utilized as the common method to resolve this RFA problem [31].