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Thursday, July 19, 2018

Quantification of combined effects of transarterial embolization and microwave ablation 


Summary


Combining percutaneous ablation and transarterial embolization for treatment of tumors, including hepatocellular carcinoma (HCC), has been of interest for some time. Although each are effective as monotherapy, improved oncologic outcomes can theoretically be achieved when combining the therapies, especially if the tumor is large or infiltrative. It stands to reason that if the cooling effect from hepatic arterial blood flow can be decreased by first performing an arterial embolization, then ablation efficacy can be improved.

Researchers from Mayo Clinic in Rochester and University of Wisconsin-Madison recently published their results quantifying the effect of embolization on microwave ablation (MW) in an in vivo porcine liver model. They studied the effects of combined MW ablation and embolization in 6 swine. Hepatic artery catheterization was performed in each animal and embolization of 2 of the 4 liver lobes was performed using 100-300 um trisacryl gelatin microspheres. MW ablations were then done in an open manner within each liver lobe immediately after embolization using a 2.45-GHz system and single 17- gauge antenna. They performed cone-beam CT at short intervals during ablation to evaluate gas formation. Diameter, length, area and circularity of ablation zones were measured on gross tissue sections and microscopic and histologic evaluation of both embolized and nonembolized tissue sections performed. They found that the embolization/MW ablation zones had a significantly greater area (mean ± standard deviation, 11.8 cm2 ± 2.5), length (4.8 cm ± 0.5), and diameter (3.1 cm ± 0.6) compared with MW ablation alone (7.1 cm2 ± 1.9, 3.7 cm ± 0.6, 2.4 cm ± 0.3, respectively). CT showed faster and greater gas formation around the antennae in the embolized lobes. Both groups showed a central charred zone and a peripheral zone of noncharred coagulated tissue. However, only the MW group showed a hemorrhagic zone beyond the noncharred coagulated zone. It was this noncharred zone that was responsible for the larger size of the ablation zone in the embolization/MW ablation group (1.3 cm ± 0.4 vs 0.8 cm ± 0.2).



Figure. Gross pathologic specimens demonstrate increased size of the embolization/MW ablation zone (a) compared with MW ablation only (b). The increased size of the ablation zone was predominantly the result of a wider peripheral noncharred coagulative zone (asterisks). The charred central portion (triangles) was not significantly different between the groups (P 1⁄4 .2611).

Commentary


While other studies have shown the clinical benefits of combining transarterial embolization with ablation, the effects have not been well quantified. This study is a step towards gaining an understanding of how combining these therapies influences the ablation zone-embolizing first can be theorized to promote coagulation in tissue that otherwise may not be affected due to persistent arterial flow-and hopefully, ultimately, allowing one to predict the enhanced ablation zone when this technique is utilized. Of course, more studies are necessary to determine whether combination therapy has the same effect on the ablation zone in tumoral, cirrhotic livers and also whether chemoembolization makes a difference.

Click here for abstract

Knavel EM, Green CM, Gendron-Fitzpatrick A, Brace CL, Laeseke PF. Combination Therapies: Quantifying the Effects of Transarterial Embolization on Microwave Ablation Zones. Journal of vascular and interventional radiology : JVIR. 2018;29:1050-1056.

Post Author
Zagum Bhatti, MD
Assistant Professor
Department of Radiology, Interventional Radiology Division
University of Texas Health Science Center at Houston, Houston, TX
@UTHouston_IR
@ZagumBhatti

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