Real-time virtual sonography-assisted radiofrequency ablation in liver tumors with conspicuous or inconspicuous images or peritumoral landmarks under ultrasonography

A total of 962 patients underwent RVS-assisted RFA in our liver unit from January 2015 to December 2016. Seven hundred forty-three (743) patients were excluded due to their previous treatments (739 patients with previous RFA, TACE, PEI), CTP C (2 patients), and > 5 cm tumor sizes (2 patients). Thus, a total of 219 patients with 315 liver tumors who underwent first-time RFA with the aid of RVS were included from the database of four interventional hepatologists. Conventional ultrasound using convex probe was done, and tumors were classified as conspicuous or inconspicuous (Fig. 2). Based on the study of CH Lee et al. [15], a detectable lesion under conventional US was defined as a lesion where the margin and echogenicity of the index tumor was visible, whereas an undetectable lesion was one in which the margin and echogenicity of the index tumor were not visible. In the inconspicuous tumor group, we subgrouped patients based on the presence or absence of peritumoral anatomical landmark (Fig. 2). A fixed anatomical landmark with less than 1 cm distance from index tumor was used since these landmarks (vessels and bile duct) were contributory factors in the identification of the tumors. A peritumoral anatomic landmark was defined as any ultrasound-discernible structure near the index tumor such as focal hepatic lesions (cysts, calcification, and previous ablation zone), bifurcation of the hepatic or portal vein, or liver configuration [16]. CT or MRI arterial-venous-wash-out cross-sectional studies were synchronized with real-time US images [17, 18].

A 17-cm gauge radiofrequency electrode with 2–3 cm active tip and an internal cooling system attached to the radiofrequency generators were used. In some cases, multiple RF electrodes with switch control were utilized. Either artificial ascites or pleural effusion was done prior to RFA for tumors in high-risk locations. After application of aseptic technique, 10 ml of 1% lidocaine was injected through the skin. The RF electrodes were inserted percutaneously into the target tumor under real-time US with RVS guidance. All RFAs were done under conscious sedation with the use of Midazolam and Fentanyl. The vital signs and oxygen saturation were monitored during the procedure. Patients were discharged less than 48 hours after post-RFA ultrasound evaluation.

Contrast imaging with CT or MRI was done within 1 month after RFA to assess complete ablation or residual viable tumors in both HCC and metastasis group. A complete response was confirmed by a dynamic CT showing a widely low-density area with sufficient safety margin [9]. A tumor was labeled as residual and viable if it was with peripheral enhancement in the arterial phase [12]. Primary technique effectiveness is defined as prospectively defined time point at which complete ablation of macroscopic tumor, as evidenced by imaging follow-up [7]. In this study, we classified as primary technique effectiveness if first follow-up contrast CT or MRI after RFA did not show any viable tumor and with sufficient safety margin. Repeat RFA, booster PEI, and TACE were options for viable tumors based on the discretion of the attending physicians. For tumors that underwent second and third RFA sessions, complete response to ablation was also assessed by contrast imaging. Contrast CT or MRI was then repeated every 3 months to assess local recurrence in tumors with complete response after first ablation. Local recurrence was defined as new tumor focus at the ablative margin after local eradication of all tumor cells with ablation [7].