The relationship between applied energy and ablation zone volume in patients with hepatocellular carcinoma and colorectal liver metastasis

Abstract

Objectives: To study the ratio of ablation zone volume to applied energy in computed tomography (CT)-guided radiofrequency ablation (RFA) and microwave ablation (MWA) in patients with hepatocellular carcinoma (HCC) in a cirrhotic liver and in patients with colorectal liver metastasis (CRLM).

Methods: In total, 90 liver tumors, 45 HCCs in a cirrhotic liver and 45 CRLMs were treated with RFA or with one of two MWA devices (MWA_A and MWA_B), resulting in 15 procedures for each tumor type, per device. Device settings were recorded and the applied energy was calculated. Ablation volumes were segmented on the contrast-enhanced CT scans obtained 1 week after the procedure. The ratio of ablation zone volume in milliliters to applied energy in kilojoules was determined for each procedure and compared between HCC (R_HCC) and CRLM (R_CRLM), stratified according to ablation device.

Results: With RFA, R_HCC and R_CRLM were 0.22 mL/kJ (0.14-0.45 mL/kJ) and 0.15 mL/kJ (0.14-0.22 mL/kJ; p = 0.110), respectively. With MWA_A, R_HCC was 0.81 (0.61-1.07 mL/kJ) and R_CRLM was 0.43 (0.35-0.61 mL/kJ; p = 0.001). With MWA_B, R_HCC was 0.67 (0.41-0.85 mL/kJ) and R_CRLM was 0.43 (0.35-0.61 mL/kJ; p = 0.040).

Conclusions: With RFA, there was no significant difference in energy deposition ratio between tumor types. With both MWA devices, the ratios were higher for HCCs. Tailoring microwave ablation device protocols to tumor type might prevent incomplete ablations.

Key points: • HCCs and CRLMs respond differently to microwave ablation • For MWA, CRLMs required more energy to achieve a similar ablation volume • Tailoring ablation protocols to tumor type might prevent incomplete ablations.

Keywords: Ablation techniques; Carcinoma, Hepatocellular; Liver diseases; Multidetector computed tomography; Radiology, Interventional.

Fig. 1

Regression analysis of the relationships between applied energy and (a) ablation zone volume for the three devices, (b) ablation zone volume obtained with the RFA device (Boston Scientific Corp.) grouped by tumor type, (c) ablation zone volume obtained with the MWA device A (Microsulis Medical) grouped by tumor type, and (d) ablation zone volume obtained with the MWA device B (Covidien) grouped by tumor type (CRLM colorectal liver metastasis, HCC hepatocellular carcinoma)

Fig. 2

Left Preprocedural portal venous phase contrast enhanced CT images of HCC in segment 6 (top) and CRLM in segment 4 (bottom) in two patients who had not received systemic therapy or transarterial (chemo)embolization. Using MWA device B, 96 kJ (100 W for 8:00 min × 2) and 96 kJ (100 W for 6:00 min, 100 W for 10:00 min) were applied to the HCC and CRLM, respectively, with 16 mm and 14 mm between the two positions of the ablation center of the antenna, so overlap was approximately similar. Right Resulting ablation zones after segmentation on the 1-week follow-up portal venous phase contrast-enhanced CT images using the MM Oncology package (syngo.via; Siemens, Erlangen, Germany), with ablation zone volumes of 96 mL and 39 mL, resulting in energy deposition ratios of 1.00 mL/kJ and 0.41 mL/kJ for HCC and CRLM, respectively. After 6 months of follow-up, the HCC showed no sign of recurrence, whereas a PET scan of the CRLM showed activity at the dorsal side of the ablation zone, for which re-ablation was performed