Timothy J. Ziemlewicz

Percutaneous Tumor Ablation Tools: Microwave, Radiofrequency, or Cryoablation—What Should You Use and Why?

Image-guided thermal ablation is an evolving and growing treatment option for patients with malignant disease of multiple organ systems. Treatment indications have been expanding to include benign tumors as well. Specifically, the most prevalent indications to date have been in the liver (primary and metastatic disease, as well as benign tumors such as hemangiomas and adenomas), kidney (primarily renal cell carcinoma, but also benign tumors such as angiomyolipomas and oncocytomas), lung (primary and metastatic disease), and soft tissue and/or bone (primarily metastatic disease and osteoid osteomas). Each organ system has different underlying tissue characteristics, which can have profound effects on the resulting thermal changes and ablation zone. Understanding these issues is important for optimizing clinical results. In addition, thermal ablation technology has evolved rapidly during the past several decades, with substantial technical and procedural improvements that can help improve clinical outcomes and safety profiles. Staying up to date on these developments is challenging but critical because the physical properties underlying the different ablation modalities and the appropriate use of adjuncts will have a tremendous effect on treatment results. Ultimately, combining an understanding of the physical properties of the ablation modalities with an understanding of the thermal kinetics in tissue and using the most appropriate ablation modality for each patient are key to optimizing clinical outcomes. Suggested algorithms are described that will help physicians choose among the various ablation modalities for individual patients.

Patient and Tumor Characteristics can Predict Nondiagnostic Renal Mass Biopsy Findings

PURPOSE Identification of patient and tumor characteristics associated with nondiagnostic biopsies is necessary to improve prebiopsy counseling and patient selection. MATERIALS AND METHODS We reviewed the clinical records and prebiopsy imaging of all patients treated with percutaneous biopsy for a renal mass 7 cm or less. Univariate and multivariate logistic regression models were constructed to examine the association between biopsy outcome and clinical/radiographic features. RESULTS A total of 565 biopsies of renal tumors 7 cm or less in 525 patients were included in the study. There was no significant difference in age, body mass index, Charlson comorbidity score or gender between the patient cohorts with diagnostic and nondiagnostic biopsy. In 83 of 565 patients (14.7%) overall and in 72 of the 413 (17.4%) with a mass of 4 cm or less the biopsy findings were nondiagnostic. Overall 14.7% of masses were cystic and 85.3% were solid with a median tumor size of 2.75 cm (IQR 2.05-4.25). Independent predictors of nondiagnostic biopsy included cystic features, enhancement less than 20 HU, left tumor, tumor diameter and skin-to-tumor distance. The nondiagnostic rate of repeat biopsies was 20.8%, which did not statistically differ from the nondiagnostic rate at the initial renal mass biopsy attempt. Radiologist or pathologist experience was not associated with the biopsy nondiagnostic rate. In 7 of 565 patients (1.2%) hospital admission was required for adverse events after biopsy. CONCLUSIONS Nondiagnostic renal mass biopsies are more common in cystic, nonenhancing, small masses when patients have a skin-to-tumor distance of 13 cm or greater. Excluding patients with these criteria decreased the nondiagnostic rate from 14.7% to 8.7%.

Liver Ablation: Best Practice

Tumor ablation in the liver has evolved to become a well-accepted tool in the management of increasing complex oncologic patients. At present, percutaneous ablation is considered first-line therapy for very early and early hepatocellular carcinoma and second-line therapy for colorectal carcinoma liver metastasis. Because thermal ablation is a treatment option for other primary and secondary liver tumors, an understanding of the underlying tumor biology is important when weighing the potential benefits of ablation. This article reviews ablation modalities, indications, patient selection, and imaging surveillance, and emphasizes technique-specific considerations for the performance of percutaneous ablation.

Percutaneous Microwave Ablation of Hepatocellular Carcinoma with a Gas-Cooled System: Initial Clinical Results with 107 Tumors

PURPOSE To retrospectively review the results of hepatocellular carcinoma (HCC) treatment with a high-power, gas-cooled, multiantenna-capable microwave device. MATERIALS AND METHODS A total of 107 HCCs in 75 patients (65 men) with a mean age of 61 years (range, 44-82 y) were treated via percutaneous approach. Combination microwave ablation and transarterial chemoembolization was performed for 22 tumors in 19 patients with tumors larger than 4 cm (n = 10), tumors larger than 3 cm with ill-defined margins (n = 7), or lesions not identified with ultrasonography (n = 5). Mean tumor size was 2.1 cm (range, 0.5-4.2 cm), with median follow-up of 14 months, for ablation alone; compared with 3.7 cm (range, 1.0-7.0 cm) and 12 months, respectively, for combination therapy. All procedures were performed with a single microwave system (Certus 140) with one to three 17-gauge antennas. RESULTS Mean ablation time was 5.3 minutes (range, 1-11.5 min). All treatments were considered technically successful in a single session. Primary technique effectiveness rates were 91.6% (98 of 107) overall, 93.7% (89 of 95) for tumors 4 cm or smaller, and 75.0% (nine of 12) for tumors larger than 4 cm; and 91.8% (78 of 85) for ablation alone and 90.9% (20 of 22) for combination therapy. There was no major complication or procedure-related mortality. The overall survival rate was 76.0% at a median 14-month clinical follow-up, with most deaths related to end-stage liver disease (n = 11) or multifocal HCC (n = 5). CONCLUSIONS Treating HCC with a gas-cooled, multiantenna-capable microwave ablation device is safe, with promising treatment effectiveness.

Microwave ablation of malignant hepatic tumours: Intraperitoneal fluid instillation prevents collateral damage and allows more aggressive case selection

Abstract Purpose: Theaim of this peper was to retrospectively review our experience utilising protective fluid instillation techniques during percutaneous microwave ablation of liver tumours to determine if fluid instillation prevents non-target injuries and allows a more aggressive case selection. Materials and methods: This institute review board-approved, US Health Insurance Portability and Accountability Act-compliant, retrospective study reviewed percutaneous microwave ablation of 151 malignant hepatic tumours in 87 patients, comparing cases in which protective fluid instillation was performed with those where no fluid was utilised. In cases utilising hydrodisplacement for bowel protection, a consensus panel evaluated eligibility for potential ablation without hydrodisplacement. Patient age, tumour size, local tumour progression rate, length of follow-up, complications, displacement distance/artificial ascites thickness, and treatment power/time were compared. Results: Fluid administration was utilised during treatment in 29/151 of cases: 10/29 for protection of bowel (8/10 cases not possible without fluid displacement), and 19/29 for body wall/diaphragm protection. Local tumour progression was higher when hydrodisplacement was used to protect bowel tissue; this may be due to lower applied power due to operator caution. Local tumour progression was not increased for artificial ascites. There was no difference in complications between the fluid group and controls. Conclusion: Intraperitoneal fluid administration is a safe and effective method of protecting non-target structures during percutaneous hepatic microwave ablation. While hydrodisplacement for bowel protection allows more aggressive case selection, these cases were associated with higher rates of local tumour progression.

Microwave versus Radiofrequency Ablation Treatment for Hepatocellular Carcinoma: A Comparison of Efficacy at a Single Center

PURPOSE To compare efficacy and major complication rates of radiofrequency (RF) and microwave (MW) ablation for treatment of hepatocellular carcinoma (HCC). MATERIALS AND METHODS This retrospective single-center study included 69 tumors in 55 patients treated by RF ablation and 136 tumors in 99 patients treated by MW ablation between 2001 and 2013. RF and MW ablation devices included straight 17-gauge applicators. Overall survival and rates of local tumor progression (LTP) were evaluated using Kaplan-Meier techniques with Cox proportional hazard ratio (HR) models and competing risk regression of LTP. RESULTS RF and MW cohorts were similar in age (P = .22), Model for End-Stage Liver Disease score (P = .24), and tumor size (mean 2.4 cm [range, 0.6-4.5 cm] and 2.2 cm [0.5-4.2 cm], P = .09). Median length of follow-up was 31 months for RF and 24 months for MW. Rate of LTP was 17.7% with RF and 8.8% with MW. Corresponding HR from Cox and competing risk models was 2.17 (95% confidence interval [CI], 1.04-4.50; P = 0.04) and 2.01 (95% CI, 0.95-4.26; P = .07), respectively. There was improved survival for patients treated with MW ablation, although this was not statistically significant (Cox HR, 1.59 [95% CI, 0.91-2.77; P = .103]). There were few major (≥ grade C) complications (2 for RF, 1 for MW; P = .28). CONCLUSIONS Treating HCC percutaneously with RF or MW ablation was associated with high primary efficacy and durable response, with lower rates of LTP after MW ablation.

Microwave Ablation: Comparison of Simultaneous and Sequential Activation of Multiple Antennas in Liver Model Systems

PURPOSE To compare microwave ablation zones created by using sequential or simultaneous power delivery in ex vivo and in vivo liver tissue. MATERIALS AND METHODS All procedures were approved by the institutional animal care and use committee. Microwave ablations were performed in both ex vivo and in vivo liver models with a 2.45-GHz system capable of powering up to three antennas simultaneously. Two- and three-antenna arrays were evaluated in each model. Sequential and simultaneous ablations were created by delivering power (50 W ex vivo, 65 W in vivo) for 5 minutes per antenna (10 and 15 minutes total ablation time for sequential ablations, 5 minutes for simultaneous ablations). Thirty-two ablations were performed in ex vivo bovine livers (eight per group) and 28 in the livers of eight swine in vivo (seven per group). Ablation zone size and circularity metrics were determined from ablations excised postmortem. Mixed effects modeling was used to evaluate the influence of power delivery, number of antennas, and tissue type. RESULTS On average, ablations created by using the simultaneous power delivery technique were larger than those with the sequential technique (P < .05). Simultaneous ablations were also more circular than sequential ablations (P = .0001). Larger and more circular ablations were achieved with three antennas compared with two antennas (P < .05). Ablations were generally smaller in vivo compared with ex vivo. CONCLUSION The use of multiple antennas and simultaneous power delivery creates larger, more confluent ablations with greater temperatures than those created with sequential power delivery.

Opportunistic Osteoporosis Screening: Addition of Quantitative CT Bone Mineral Density Evaluation to CT Colonography.

PURPOSE For patients undergoing CT colonography (CTC), the screening presents an opportunity for concurrent osteoporosis screening, without increasing radiation exposure or the time involved for the patient, using proximal femur quantitative CT-CT x-ray absorptiometry (QCT-CTXA). METHODS This cohort included 129 women and 112 men (mean age: 60.1 ± 8.2 years; range: 50-95 years) who underwent CTC between March 2013 and September 2014. Areal bone mineral density (BMD; g/cm(2)), and resultant left femoral neck T-score, was prospectively measured on the supine CT series. QCT results were reported with the CTC. Chart review evaluated whether the patients were eligible for BMD screening according to guidelines from the US Preventive Services Task Force and the National Osteoporosis Foundation guidelines; whether they had undergone prior BMD testing; and whether QCT results changed patient management. RESULTS Overall, 68.0% (164 of 241) of patients from this cohort had not previously undergone BMD screening. According to the National Osteoporosis Foundation guidelines, 44.0% (106 of 241) of patients were eligible for screening. T-scores within the osteopenic and osteoporotic range were detected in 32.3% (78 of 241) and 5.0% (12 of 241) of patients, respectively. Of these patients with low BMD, 66.7% (60 of 90) either had not previously undergone screening or were eligible for BMD testing. Reporting of QCT-CTXA T-scores altered management in 9 patients (3.7%) who had low BMD. CONCLUSIONS Maximizing the pre-existing value from imaging studies is crucial in the current era of health care reform. We demonstrate that colorectal and osteoporosis screening can be combined at CT examination, adding clinical and likely economic value.

Direct Comparison of Unenhanced and Contrast-Enhanced CT for Opportunistic Proximal Femur Bone Mineral Density Measurement: Implications for Osteoporosis Screening

OBJECTIVE For patients undergoing contrast-enhanced CT examinations that include the proximal femur, an opportunity exists for concurrent screening bone mineral density (BMD) measurement. We investigated the effect of IV contrast enhancement on CT-derived x-ray absorptiometry areal BMD measurement. MATERIALS AND METHODS Our cohort included 410 adults (mean age, 65.3 ± 10.0 years; range, 49-95 years) who underwent split-bolus CT urography at 120 kVp. Areal femoral neck BMD in g/cm(2) was measured on both unenhanced and contrast-enhanced CT series with asynchronous phantom calibration. Constant offset and multiplicative factor corrections for the contrast-enhanced series were derived from the Bland-Altman plot linear regression slopes. RESULTS Mean unenhanced and contrast-enhanced areal femoral neck BMD values were 0.681 ± 0.118 and 0.713 ± 0.123 g/cm(2), respectively. The SD of the distribution of residuals for the constant offset and multiplicative model corrections were 0.0232 and 0.0231, respectively. The constant offset correction associated with contrast enhancement was 0.032 ± 0.023 g/cm(2), which corresponds to 0.29 ± 0.21 T-score units using the CT-derived x-ray absorptiometry young normal areal femoral neck BMD reference SD of 0.111 g/cm(2). CONCLUSION For the purposes of opportunistic osteoporosis screening, contrast-enhanced abdominopelvic CT studies are equivalent to unenhanced CT and can therefore be used for femoral neck BMD assessment. This measure could greatly enhance osteoporosis screening.

Opportunistic Quantitative CT Bone Mineral Density Measurement at the Proximal Femur Using Routine Contrast-Enhanced Scans: Direct Comparison With DXA in 355 Adults

For patients undergoing routine contrast‐enhanced CT examinations, an opportunity exists for concurrent osteoporosis screening without additional radiation exposure or patient time using proximal femur CT X‐ray absorptiometry (CTXA). We investigated the effect of i.v. contrast enhancement on femoral neck CTXA T‐score measurement compared with DXA. This cohort included 355 adults (277 female; mean age, 59.7 ± 13.3 years; range, 21 to 90 years) who underwent standard contrast‐enhanced CT assessment at 120 kVp over an 8‐year interval, as well as DXA BMD assessment within 100 days of the CT study (mean 46 ± 30 days). Linear regression and a Bland‐Altman plot were performed to compare DXA and CTXA results. CTXA diagnostic sensitivity and specificity was evaluated with DXA as the reference standard. There was good correlation between DXA and CTXA (r2 = 0.824 for both areal BMD and T‐scores) and the SD of the distribution of residuals was 0.063 g/cm2 or 0.45 T‐score units. There was no trend in differences between the two measurements and a small bias was noted with DXA T‐score +0.18 units higher than CTXA. CTXA had a sensitivity for discriminating normal from low bone mineral density of 94.9% (95% CI, 90.6% to 97.4%). For opportunistic osteoporosis screening at routine post‐contrast abdominopelvic CT scans, CTXA produces T‐scores similar to DXA. Because femoral neck CTXA BMD measurement is now included in the WHO Fracture Risk Assessment Tool (FRAX) tool, this opportunistic method could help to increase osteoporosis screening because it can be applied regardless of the clinical indication for CT scanning.