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Radiofrequency Thermal Ablation

Computer Analysis of the Size of the Thermal Injury Created by Overlapping Ablations

¹ Department of Radiology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr., San Antonio, TX 78284.
² Present address: Department of Radiology, Massachusetts General Hospital, 55 Fruit St., Boston, MA 02114.

View larger version (158K): [in a new window]   Fig. 1A. —56-year-old man with hepatocellular carcinoma. Enhanced CT scan obtained before ablation shows 2.5-cm hepatocellular carcinoma.

View larger version (139K): [in a new window]   Fig. 1B. —56-year-old man with hepatocellular carcinoma. Enhanced CT scan obtained at the same level as A 6 months after tumor was treated with single 3-cm ablation shows ablation area equal to size of tumor with no residual tumor detected.

View larger version (160K): [in a new window]   Fig. 1C. —56-year-old man with hepatocellular carcinoma. Resected liver specimen 6 months after ablation shows residual tumor (arrows) not revealed at CT.

View larger version (80K): [in a new window]   Fig. 2. —Computer representation of single-ablation model. Effective ablation must encompass tumor plus 360° 1-cm tumor-free margin. Computer drawing depicts tumor plus half of effective tumor-free margin (red sphere). This 360° margin adds 2 cm to overall diameter of ablation sphere, depicting ablation volume encompassing tumor and tumor-free margin.

View larger version (72K): [in a new window]   Fig. 3A. —Computer representation of construction of six-sphere thermal ablation model. Six-sphere ablation model is constructed by performing four ablations in the x-y plane (A-C sequentially) and two along the z-axis (D). Green sphere represents total volume of tissue requiring ablation (tumor plus 1-cm tumor-free margin), and red spheres represent individual thermal ablation spheres that are being overlapped. Largest composite ablation sphere is created when all spheres are overlapped by approximately 23% of diameter.

View larger version (76K): [in a new window]   Fig. 3B. —Computer representation of construction of six-sphere thermal ablation model. Six-sphere ablation model is constructed by performing four ablations in the x-y plane (A-C sequentially) and two along the z-axis (D). Green sphere represents total volume of tissue requiring ablation (tumor plus 1-cm tumor-free margin), and red spheres represent individual thermal ablation spheres that are being overlapped. Largest composite ablation sphere is created when all spheres are overlapped by approximately 23% of diameter.

View larger version (90K): [in a new window]   Fig. 3C. —Computer representation of construction of six-sphere thermal ablation model. Six-sphere ablation model is constructed by performing four ablations in the x-y plane (A-C sequentially) and two along the z-axis (D). Green sphere represents total volume of tissue requiring ablation (tumor plus 1-cm tumor-free margin), and red spheres represent individual thermal ablation spheres that are being overlapped. Largest composite ablation sphere is created when all spheres are overlapped by approximately 23% of diameter.

View larger version (96K): [in a new window]   Fig. 3D. —Computer representation of construction of six-sphere thermal ablation model. Six-sphere ablation model is constructed by performing four ablations in the x-y plane (A-C sequentially) and two along the z-axis (D). Green sphere represents total volume of tissue requiring ablation (tumor plus 1-cm tumor-free margin), and red spheres represent individual thermal ablation spheres that are being overlapped. Largest composite ablation sphere is created when all spheres are overlapped by approximately 23% of diameter.

View larger version (109K): [in a new window]   Fig. 4A. —Computer representation of six-sphere thermal ablation model depicting overlapping ablation spheres that will create composite spherical ablation encompassing tumor and tumor-free margin. Six-sphere model shows fissures at intersection of spheres.

View larger version (100K): [in a new window]   Fig. 4B. —Computer representation of six-sphere thermal ablation model depicting overlapping ablation spheres that will create composite spherical ablation encompassing tumor and tumor-free margin. Cross-section through middle of model shows that maximum composite spherical ablation (green area) does not touch margins at midsection.

View larger version (111K): [in a new window]   Fig. 4C. —Computer representation of six-sphere thermal ablation model depicting overlapping ablation spheres that will create composite spherical ablation encompassing tumor and tumor-free margin. Size of composite spherical ablation (green area) is limited by "pits" at intersection of three spheres.

View larger version (90K): [in a new window]   Fig. 4D. —Computer representation of six-sphere thermal ablation model depicting overlapping ablation spheres that will create composite spherical ablation encompassing tumor and tumor-free margin. Cut section of model shows size of tumor that can be adequately treated (yellow area), taking 1-cm tumor free margin (green area) into account.

View larger version (82K): [in a new window]   Fig. 5A. —Computer representation of 14-sphere thermal ablation model. Six-ablation model shows untreated tissue (green areas) at each pit.

View larger version (113K): [in a new window]   Fig. 5B. —Computer representation of 14-sphere thermal ablation model. Eight additional spheres (in blue) are used to cover eight pits.

View larger version (101K): [in a new window]   Fig. 5C. —Computer representation of 14-sphere thermal ablation model. Cross-section through middle of 14-sphere ablation model shows maximum diameter of composite spherical ablation (green area) that is 1.66 times diameter of single ablation.

View larger version (83K): [in a new window]   Fig. 5D. —Computer representation of 14-sphere thermal ablation model. Cut section of model shows size of tumor that can be adequately treated (yellow sphere) taking 1-cm tumor-free margin (green area) into account.

View larger version (74K): [in a new window]   Fig. 6A. —Computer representation of cylindrical thermal ablation model. Thermal ablation cylinders are created by overlapping multiple ablation spheres by 58%.

View larger version (79K): [in a new window]   Fig. 6B. —Computer representation of cylindrical thermal ablation model. Overlapping of ablation cylinders creates rectangular ablation columns made up of individual ablation cubes.

View larger version (41K): [in a new window]   Fig. 6C. —Computer representation of cylindrical thermal ablation model. Sides of each ablation cube are equal to 0.58 times diameter of individual ablation sphere.

View larger version (70K): [in a new window]   Fig. 6D. —Computer representation of cylindrical thermal ablation model. Ablation cylinders are systematically overlapped to ablate large tumors.

View larger version (146K): [in a new window]   Fig. 7. —Varying sizes of thermal ablation injury by different radiofrequency ablation devices. Cirrhotic liver of 63-year-old woman shows varying sizes and shapes of ablations (arrows) created before liver resection with three different radiofrequency ablation devices from different manufacturers. Marked variation emphasizes need for systematic ablation protocol.

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