Oncology: Animal/experimental

Scientific Session 20

Oncology: Animal/Experimental

Monday, March 5, 20078:00 AM - 10:00 AMRoom: 2058:00 AM Abstract No. 177FEATURED ABSTRACTRFA Induces a Tumor-Specific Immune Response: ANew Role for RFA in Immunotherapy.S.A. Dromi, Clinical Center, National Institute of Health,Bethesda, MD, USA � S. Herby � M. Walsh � D. Sudheendra� T. Fry � B. Wood

PURPOSE: Spontaneous or targeted destruction of tumorpotentially activates T cell responses to tumor-associatedantigens through cross presentation by antigen presentingcells. Tumor ablation with a thermal energy source, such asradiofrequency ablation (RFA) may enhance native immuneresponses via increased antigen availability or factors pro-duced or released in response to RFA.

MATERIALS AND METHODS: Fifty C57BL/6 mice bear-ing HY-expressing tumors (MB49) were treated with RFAor left untreated. When tumors reach approximately 500mm3 RFA was delivered for 70 seconds at approximately90°C using a Radionics® RF lesion generator System(model RFG-3C Plus) with a Radionics® SMK 22-gaugeneedle with 4-mm active tip that was inserted through theskin in the center of the tumor for partial ablation. After 14days, splenocytes were assayed for the number of CD4 andCD8 T cells producing interferon gamma in response to theMHC class I dominant (UTY), class I subdominant (SMCY)and class II dominant (Dby) epitopes derived from the HYcomplex using ELISPOT. Total CD4 and CD8 T cells wereenumerated by flow cytometry.

RESULTS: Untreated tumor-bearing mice demonstrate bothCD4 and CD8 HY immunity, but were unable to controltumor growth. We have previously demonstrated that vac-cination of female mice with male dendritic cells (DC)results in enhanced tumor protection. In this study, RFAtreatment of HY expressing tumors resulted in HY immu-nity that was significantly higher than untreated tumor-bearing mice and is similar in magnitude to that observed inmale DC-vaccinated mice. Tumor-specific class II re-sponses showed the most significant increase (Dby, p �0.00002) followed by dominant class I (UTY, p � 0.0006)antigen. The smallest significant increase was seen in sub-dominant class I responses (SMCY, p � 0.02). There wereno differences in the total number of CD4 and CD8 T cellsin the spleens or lymph nodes of treated and untreated mice.

CONCLUSION: RFA can enhance systemic immune re-sponses against tumor antigens. This tumor-specific ap-proach should be studied in combination with immune-based antitumor therapy such as vaccines, adoptive celltransfer, or local infusion of immunoactive agents.

8:15 AM Abstract No. 178

Contrast-enhanced MR Imaging after Cryoablation ofthe Canine Prostate: Imaging the Acute Avascular Zone.M.A. van den Bosch, Stanford University Medical Center,Stanford, CA, USA � S. Josan � K. Butts-Pauly � D.M. Bouley� B.L. Daniel

PURPOSE: To assess the correlation between iceball sizeand size of the acute avascular zone, induced by freezing ofcanine prostates, as estimated from contrast-enhanced mag-netic resonance imaging (CE-MRI). Furthermore, we as-sessed the impact of different freezing protocols on the sizeof the acute avascular zone relative to total iceball size.

MATERIALS AND METHODS: Eight adult male mixedbreed dogs were preanesthetized, intubated, and placed inthe 0.5-T Signa open MR system. A receive only endorectalcoil was placed in the rectum. MR compatible cryoablationprobes and fiberoptic temperature sensors were insertedthrough the anterior abdominal wall into the prostate. Threedifferent freezing protocols were used: A) single probeablation, final temperature between 0°C and -5°C, onefreeze/thaw cycle; B) single probe ablation, final tempera-ture � -40°C, two freeze/thaw cycles; C) multiple probeablation, final temperature between 0°C and -5°C, onefreeze/thaw cycle. The size of the acute cryolesions wasevaluated with T2-weighted MR images and directly post-procedural with CE T1-weighted images after administra-tion of contrast medium. MR images were analyzed andmanually segmented using ImageJ software for windows.

RESULTS: A total of 16 cryolesions (mean size 1.2 cm)were bilaterally created in 8 canine prostates. Direct post-procedural CE-MRI typically showed a low signal intensity,avascular zone, centrally located within the frozen area,surrounded by a bright enhancing rim in all cases (n � 16).When the manually segmented area of low signal intensitywas superimposed on the non-contrast T2-weighted imagesof the iceball, the mean maximum size of avascular zonewas 60% of the mean maximum size of the whole iceball(range 0.44 – 0.70). The avascular zone relative to totaliceball size was the largest in group B lesions, i.e. 64%versus 56% in group A and 60% in group, respectively.

CONCLUSION: Contrast-enhanced MR imaging of acutecryolesions in canine prostates showed the true avascularzone, representing lethal tissue injury, centrally within theiceball. Clinically, accurate visualization of this zone isessential to allow successful image-guided cryoablation ofprostate cancer.


Minimum Safety Distances from Critical Non-TargetStructures for RF Ablation: A Computer ModelingStudy.Z. Liu, Beth Israel Deaconess Medical Center, Boston, MA,USA � M. Ahmed � S. Humphries � S.N. Goldberg

PURPOSE: To use computer modeling to characterize fac-tors that influence the minimum safe distances requiredbetween an activated RF electrode and adjacent non-targetcritical structures.

MATERIALS AND METHODS: Computer simulation(Etherm) of RF heating evaluated the effect of tissue com-position, tissue perfusion, electrode orientation, and elec-trode type on heating of adjacent, non-target critical struc-tures (n � 2,256 simulations). The tissue between theelectrode and the critical structure was varied from 5–25mm and standardized to tumor and/or fat (thermal conduc-tivity 0.46 & 0.23 W/m-°C, electrical conductivity 0.5 & 0.1S/m, and perfusion 0.5 & 0.1 kg/m3-s, respectively). Theeffect of varying tumor perfusion (0-5 kg/m3-s) was alsoevaluated. Finally, electrode orientation (parallel or perpen-dicular to the tissue), and electrode type (non-cooled &internally-cooled 3 cm single or 2.5 cm cluster electrodes)

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were studied. The time required to reach 50°C (t50) and thesafe distance to avoid t50 at the margin of an adjacentcritical structure were compared.

RESULTS: In all cases, increasing the amount of interven-ing fat increased t50, compared to soft tissue. For singlecooled electrodes, the amount of intervening fat and/orsoft-tissue to prevent damage decreased linearly with in-creasing perfusion (y � -0.48 � �12.4, R2 � 0.74 parallel;and y � -0.57 � �8.8, R2 � 0.98 for perpendicular). Withno perfusion, 9 mm of intervening fat or 14 mm of softtissue was required for perpendicular insertion, compared to12 mm of fat and 23 mm of soft tissue for a parallelinsertion. Finally, less intervening tissue was needed fornon-cooled electrodes compared to cooled electrodes, witheven more intervening tissue required for cluster electrodes.

CONCLUSION: The thermal and perfusion characteristicsbetween the electrode and adjacent non-target critical struc-ture affect the minimum safe distance required for prevent-ing thermal injury. The presence of fat may be beneficial inpreventing injury, especially for hypovascular tumors.Lastly, when there is concern for adjacent injury, perpen-dicular rather than parallel electrode orientation may be auseful strategy to minimize injury.


Development of New Image-Guiding System Using Su-perimposing Technique for Percutaneous AblationTherapy.M. Hamuro, Osaka City University Graduate School ofMedicine, Osaka, Japan � H. Matsui � Y. Sakai � N. Nishida� T. Matsuoka � K. Nakamura

PURPOSE: The purpose of this study is to develop a newimage-guiding system using superimposing technique inpercutaneous ablation therapy for hepatic tumors with dif-ficult depiction on ultrasonography (US) alone.

MATERIALS AND METHODS: CT images that depicted thetumors clearly were captured as reference images with acharge-coupled device camera. The reference image wassuperimposed on real-time US image by using a videosignal mixer. In this process, scale and arrangement of thereference image were adjusted so that contours of the liverand the hepatic vessels of the reference image and those ofreal-time US image might completely overlap each other.Needle insertion was carried out under the real time USguidance on which the reference image was superimposed.Ablation was started after checking that the inserted needlehit the target on the CT image taken immediately afterpuncture. We performed percutaneous ablation therapy un-der this new guiding system using superimposing techniquein 6 cases of hepatocellular carcinoma with difficult depic-tion by US. Radiofrequency ablation was performed in 4cases and percutaneous ethanol injection therapy (PEIT)was performed in 2 cases. The average diameter of thetumors was 2.2 cm and the average number of needleinsertion was 1.8 times / session.

RESULTS: The inserted needle hit the target in all caseswithout any complications. Although the very slight resid-ual lesion was recognized in one PEIT case, the tumors wereablated completely in the other five cases on the CT imagestaken a week after the ablation.

CONCLUSION: This new guiding system using superim-posing technique is feasible and useful for ablation of he-patic tumors with difficult depiction on US. Because theimages of any modalities can be superimposed, we are

planning to apply this system not only for hepatic tumorablation but also for the other image-guiding therapieswidely.


Radiofrequency and Laser Tumor Ablation — A Com-parison of Thermal Dose Requirements.P.M. Mertyna, Beth Israel Deaconess Medical Center, Bos-ton, MA, USA � A.U. Hines-Perlata � Z. Liu � S.A. Solazzo �S.N. Goldberg

PURPOSE: To compare the critical thermal dosimetry nec-essary to create RF and laser-induced coagulation.

MATERIALS AND METHODS: Ablation duration was var-ied 3–60 minutes to create defined coagulation diameters(20-40 mm) in ex-vivo bovine liver. Temperatures weremonitored continously at 10-25 mm from the applicator.Energy was applied as constant current for RF [500 kHzCC-1 generator, Valleylab] with 3 cm cool-tip electrodes(400-1200 mA in 100 mA intervals)[N � 114]; 45 ablationswere created using an SLT laser (Photomedex) with a 3 cmcooled diffusing fiber in a continuous mode (5-30 Watts in5-W intervals). Mathematical calculations of thermal end-points: 1) maximum temperature at the ablation margin, 2)total amount of heat delivered during the ablation (AUC),and 3) Cumulative Equivalent Minutes at 43°C (CEM43)were correlated with ablation diameter and analyzed as afunction of delivered energy.

RESULTS: For both RF and laser, the amount of heatneeded to achieve ablation (AUC), varied with energy ap-plied and coagulation diameter as negative exponentialfunctions (R2 � 0.82-0.98). Yet, for laser the requiredthermal dose was at least 10 times higher than for RF (p �0.001). For both, the relationship between ablation durationand energy for each coagulation diameter was also a nega-tive exponent (R2 � 0.92-0.99). The maximum tempera-tures at the margin of ablation were not constant, ranging33-76°C for RF ablation and 52-72°C for laser; with tem-perature varying linearly with energy and coagulation di-ameter (R2 � 0.74-0.96). CEM43 values varied exponen-tially with energy and distance (R2 � 0.52-0.76), over awide range of values (1012).

CONCLUSION: For both RF and laser ablation in ex-vivoliver, the thermal dosimetry required to achieve coagulationis exponentially-dependent on energy dose and distancefrom the applicator. The total heat necessary to create agiven amount of coagulation is significantly higher for laseras compared to RF. These data suggest that RF ablation maynot be due to purely “thermal” effects, and may involveother interactions with tissue – possibly including electro-magnetic properties of the RF field. On the other hand, laserenergy may alter thermal or optical properties of tissue.


Pulsed-High Intensity Focused Ultrasound (HIFU) En-hanced Delivery and Produced Tumor Growth Inhibi-tion When Using Heat Sensitive Liposome Encapsulat-ing Doxorubicin (Thermodox™).S. Dromi, Clinical Center, National Institute of Health,Bethesda, MD, USA � V. Frenkel � B. Traughber � A. Luk � S.Libutti � B. Wood, et al.

PURPOSE: Pulsed-high intensity focus ultrasound (HIFU)showed increased delivery of different substances in a non-destructive manner. But, these exposures did not increase

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the delivery of non-thermosensitive liposomal doxorubicin(Doxil R) in previous studies. The purpose of the study wasto determine if the same HIFU exposures could enhancedelivery of doxorubicin and also affect tumor growth usinglow heat thermosensitive liposome (Thermodox™).

MATERIALS AND METHODS: Temperature measurementsin the tumors showed the typical elevations of 5°C thatoccur during the pulsed-HIFU exposures (1 MHz, 10% dutycycle, 1 Hz prf, 40 watts total acoustic power). Thermosen-sitive liposomes start releasing doxorubicin when heated at39°C. For 2 minutes at 42°C the thermosensitive liposomereleases approximately 50% of the cargo. For delivery stud-ies tumors were grown in both flanks of mice. For regres-sion studies tumors were grown in one flank of the mice.Mice received systemic injections of saline, DoxilR or Ther-modox™ via tail vein administration. One tumor per animalreceived pulsed-HIFU exposure. For delivery studies, thesecond tumor served as control. For regression studies,animals without HIFU treatment were used as controls.

RESULTS: Doxorubicin concentrations in the tumors ofmice receiving Thermodox™ were approximately threetimes higher in those exposed to pulsed-HIFU than in con-trols, and also higher than in the mice receiving pulse-HIFUwith DoxilR. In regression studies, tumors treated withthermosensitive liposome plus pulse HIFU were delayed forapproximately 11 days in reaching a volume of 500 mm3,compared to the approximate 7.8 days seen in tumorstreated with non-thermosensitive liposomes plus pulsed-HIFU (P � 0.0086). The remaining groups of mice didn’tpresent a significant growth inhibition.

CONCLUSION: Pulsed-HIFU exposures were found to sig-nificantly increase the delivery of doxorubicin when usingThermodox™ compared to DoxilR. This increment of doxo-rubicin in the tumors helps to both increase the efficacy oftreatments and reduce side effects of the drug.


Computer Modeling of Combined Perfusion, Electricaland Thermal Conductivity on RF Heating and TumorAblation.M. Ahmed, Beth Israel Deaconess Medical Center, Boston,MA, USA � Z. Liu � S. Humphries � S.N. Goldberg

PURPOSE: To use an established computer simulationmodel of radiofrequency (RF) ablation to characterize thecombined effects of varying tumor size, perfusion, andelectrical and thermal conductivity on RF heating.

MATERIALS AND METHODS: Two-compartment com-puter simulation of RF heating using finite element analysiswas performed (n � 2,842 simulations). Simulated RFapplication (6-20min) was systematically modeled for tu-mor diameters of 2-5 cm on a clinically relevant template oftumor and surrounding tissue perfusion (0-5kg/m3-s, each)for internally cooled 3-cm single and 2.5-cm cluster elec-trodes. First, outer thermal conductivity was changed toreflect 3 clinical scenarios: soft tissue, fat, and ascites (0.5,0.23, and 0.7 W/m-°C, respectively). Next, electrical con-ductivity was changed to reflect different tumors (0.5 and4.0 S/m, [soft tissue and saline injection, respectively]) andbackground electrical conductivity of soft tissue, lung, andkidney (0.5, 1.0, and 3.3 S/m, respectively). Finally, the“best” and “worst” combinations of thermal and electricalconductivity were modeled. Tissue heating and the timerequired to heat the entire tumor � a 5-mm margin to �50°C were assessed.

RESULTS: For all tumor sizes and electrodes, increasingbackground thermal conductivity increased the time toachieve a 50°C isotherm and enabled ablation at highertissue and/or tumor perfusion. Inner thermal conductivity ofsoft tissue surrounded by fat had the greatest tumor heatingin the shortest time, while ablation of soft tissue surroundedby ascites often could not be achieved despite increasedheating times. For varied electrical conductivity, greatestheating occurred for simulated adjuvant saline in outer softtissue, with the least heating seen for tumor in normalkidney. When assessing the “best” and “worst” clinicalscenarios, the greatest effect was seen in 3-4-cm tumors, asalmost no 5-cm tumors could be treated.

CONCLUSION: Computer modeling of RF ablation dem-onstrates that while tissue perfusion has the dominant influ-ence on heating, suboptimal thermal and electrical conduc-tivity markedly limit successful ablation except in thesetting of almost nonexistent perfusion for clinically rele-vant tumor sizes.


Doxorubicin Concentration in Chemoembolized HCC:Capillary Electrophoresis Coupled with Laser-inducedFluorescence.E.N.K. Cressman, University of Minnesota Medical School,Minneapolis, MN, USA � J. Hong � Y. Wang � C.V. Eddy �E.A. Arriaga

PURPOSE: To develop and apply capillary electrophoresiscoupled with laser-induced fluorescence to study the con-centration and distribution of doxorubicin in chemoemboli-zed tumor samples from explanted livers.

MATERIALS AND METHODS: Frozen sections 5-10 mi-crons in thickness were obtained from explants of chemo-embolized hepatomas of 5 patients who went on to trans-plant. Tissues were collected such that each piece containedboth tumor and cirrhotic parenchyma. Sampling was per-formed at room temperature in triplicate for a given slice inthree locations 3 mm apart: tumor, margin, and parenchyma.Microcapillaries (O.D. 150 microns/I.D. 50 microns) wereused to obtain samples in the nanoliter range for capillaryelectrophoretic separation. Electrophoresis was performedat 400 V/cm using a running buffer of sodium borate/sodium dodecyl sulfate. Excitation was performed with anargon laser at 488 nm and detection was at 535 � 17.5 nm(green channel, fluorescein internal standard) and 635 �27.5 nm (red channel, doxorubicin). Signal intensities andmigration times were noted in each case and correlated withinternal standards to construct response curves.

RESULTS: Two major peaks are seen with migration wellseparated in time. The early peak is seen in the fluoresceinstandard samples whereas the later peak appears in samplesknown to contain doxorubicin. The second peak corre-sponds to attomole (10-18 mole) levels of doxorubicinbased on standard curves.

Doxorubicin concentrations (nM) and locationsPatient Tumor Margin Parenchyma1 158.4 Not Det 14.542 40.72 25.28 22.713 3.02 0.44 0.154 18.70 25.90 8.765 9.40 8.34 Not Det

CONCLUSION: Capillary electrophoresis coupled with la-ser-induced fluorescence can detect and resolve doxorubicinin nanoliter-size samples of chemoembolized tumors fromexplanted livers. The method provides information on both

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drug levels and spatial distribution. Based on these results,further investigation is warranted to refine the technique.


Arterial Transportation Characteristics of Embozene™,Embosphere®, BeadBlock™ Microspheres in a PorcineKidney Model.S. Stampfl, University Hospital, Heidelberg, BW, Germany� U. Stampfl � N. Bellemann � C. Sommer � B. Radeleff � G.M.Richter, et al.

PURPOSE: Several types of spherical microparticles havebeen introduced to address the need for precise target vesseldelivery. Their baseline chemistry and inherent physicalcharacters are varying widely. Therefore, we investigatedthree different calibrated microparticles in various sizes inthe acute minipig kidney model to compare their depth ofpenetration and quality of occlusion.

MATERIALS AND METHODS: 4 size classes were embo-lized (100, 250, 500, 700 �m) in a total of 12 animals. Foreach class and material 2 organs were assigned (24 kidneystotal). Embolization was done from the main renal arteryinto the entire arterial tree until significant flow reductionwas achieved and total arterial devascularization was con-firmed angiographically. Then the organs were harvested.Particles within visible vessels were individually countedfor each kidney sample (10 per organ) and assigning them toone of four groups of vessels: (1) large vessels, (2) arcuatearteries, (3) interlobular arteries, or (4) preglomerular arter-ies.

RESULTS: In general the penetration pattern followed thesize of the applied sphere. Embozene™ microspheres in the500 or 700 �m class never reached beyond their size thresh-old. Similarly sized Embosphere® microspheres or BeadBlock™ microspheres showed a minor trend toward somemore distal propagation into the arcuate artery (� 350 �mdiameter) in the range of around 4% of all visible vessels. Inthe 100 or 250 �m size class no embolic particle (regardlessof brand) was found in preglomerular arteries (� 50 �m)indicating that all particles were adequately sieved andmechanical stable during embolization.

CONCLUSION: As the minipig kidneys fairly well simulatehuman kidney vasculature conditions the penetration patterndetected here-in probably reflects actual conditions for hu-man embolizations. The three tested microparticles showedadequate calibration and very similar penetration patternsper size class. The trend of Embospheres or Bead Block toreach slightly more distally in the 500 and 700 �m classmight be explained by their relative softness and elasticity.


Embolic Potential of Collagen-based Particles as Com-pared to PVA.G. McLennan, Indiana University Medical Center, India-napolis, IN, USA � D. Zhang � G.J. Nadolski � M.S. Khaja �M. Cao � L. Yun, et al.

PURPOSE: To determine the recanalization of collagen-based particles using enhanced contrast CT.

MATERIALS AND METHODS: In eleven New ZealandWhite rabbits, bilateral renal arteries were embolized fromthe proximal renal artery. Each kidney was embolized with0.5 mL of 900 mg of either 300-500 �m polyvinyl alcoholparticles (PVA) or 150-250 �m collagen-based particles

suspended in solution to the same viscosity. Investigatorswere blinded to the identity of the embolic material until thecompletion of the study. Animals survived for 42 days.Contrast-enhanced CT of the abdomen was performed priorto, three or four days after, three weeks after, and six weeksafter embolization. Serum creatinine and animal weightwere recorded before, after three or four days, and weeklyafter embolization. Of these, three rabbits were euthanizeddue to excessive elevations in their creatinine during followup. In seven additional rabbits, the right kidney and hepaticartery was embolized. Of these, only two animals survivedfor 42 days. These yielded ten right kidneys and eight leftkidneys that were followed for 42 days. Volumetric analysiswas performed on the CT scans to determine the volume ofrenal parenchyma enhanced at each time point. Three ani-mals (six kidneys) will undergo final CT scan on 10/4/06.

RESULTS: Percentage of renal embolization was 66.7%,and 5.8% three or four days after embolization for PVA andcollagen-based particles, respectively. After three weeks,the percentages were 73.0%, and 0.5%. After six weeks, thepercentage of embolized kidney fell to 43.0% and 0%.Serum creatinine levels in all animals that survived 42 daysstarted at 1.4 � 0.3 mg/dL and rose to 2.1 � 0.7 mg/dL forthe first week after embolization. Thereafter, the creatininelevels dropped to 1.5 � 0.4 mg/dL in week two. After theCT scan at three weeks, creatinine rose only slightly to1.7 � 0.6 mg/dL at six weeks.

CONCLUSION: PVA was able to more completely embo-lize the kidney than the collagen-based particles at equalmass and viscosity. Even with more initial embolization,after three weeks, recanalization occurred for PVA withgreater flow to the kidney by six weeks. Further research onthe concentration of collagen particles is needed.

Scientific Session 21Education and Practice Management

Monday, March 5, 20078:00 AM - 10:00 AMRoom: 210


EXpert Performance Evaluation Using Real TIme Sim-ulated Environments: Data Extracted from the EXPER-TISE Protocol.J.R. Duncan, Mallinckrodt Institute of Radiology at Wash-ington University in St. Louis School of Medicine, St. Louis,MO, USA � C.B. Glaiberman � B. Kline � B. Jacobs � A.A.Patel � M.W. Scerbo

PURPOSE: Evaluate methods of assessing performanceduring simulated renal artery stent procedures.

MATERIALS AND METHODS: The EXPERTISE protocolconsists of three parts: 1) a questionnaire regarding priorexperience, 2) a hands-on orientation session using a highfidelity endovascular simulator (Mentice VIST® or Simbio-nix AngioMentor®), and 3) a series of 1-4 trials using thesimulator for renal artery stent placement. Performance onthe trials is captured using multiple video and audio record-ers. This protocol was used by the Society of InterventionalRadiology’s Simulation Task Force to collect data fromover 40 experienced interventionalists at two national meet-ings. For data analysis, the multiple video and audio datastreams from each of the 120� simulated renal artery stent

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Oncology: Animal/experimental