Defining New Metrics in Microwave Ablation of Pulmonary Tumors: Ablation Work and Ablation Resistance Score

doi:10.1016/j.jvir.2016.05.026

Journal of Vascular and Interventional Radiology

Volume 27, Issue 9, September 2016, Pages 1380-1386

https://doi.org/10.1016/j.jvir.2016.05.026 Get rights and content

Abstract

Purpose

To investigate pulmonary microwave ablation metrics including ablation work, ablation resistance score, and involution.

Materials and Methods

Retrospective review was performed of 98 pulmonary tumor ablations using the NeuWave Certus Microwave Ablation System (NeuWave Medical, Madison, Wisconsin) in 71 patients (32 men and 39 women; mean age, 64.7 y ± 11.5). Ablation work was defined as sum of (power) * (time) * (number of antennas) for all phases during an ablation procedure. Ablation zone was measured on CT at 3 time points: after procedure, 1–3 months (mean 47 d), and 3–12 months (mean 292 d). Ablation zones were scored based on location for pulmonary lobe (upper = 1, middle/lingula = 2, lower = 3) and region (peripheral = 1, parenchymal = 2, central = 3), and the 2 were summed for ablation resistance score.

Results

Ablation zone on CT at 1–3 months was significantly smaller in regions with higher ablation resistance score (P < .05). There was a significant correlation between ablation work and ablation zone measured on CT performed after procedure (P < .001), at 1–3 months (P < .001), and at 3–12 months (P < .05). Ablation zone significantly decreased from after procedure to 1–3 months (P < .001) and from 1–3 months to 3–12 months (P < .001), with change from after procedure to 1–3 months significantly greater (P < .01).

Conclusions

Pulmonary microwave ablation zone is significantly smaller in regions with higher ablation resistance score. Ablation work correlates to ablation zone with a nonlinear involution pattern in the first year and may be useful for planning before the procedure.

Section snippets

Materials and Methods

After institutional review board approval, a retrospective chart review of 98 noncavitary pulmonary tumor ablations using a NeuWave Certus Microwave Ablation System (NeuWave Medical, Inc, Madison, Wisconsin) was performed. All cases were performed percutaneously under computed tomography (CT) guidance by 1 of 3 operators (R.D.S., F.G.A., S.J.G.) between June 2011 and July 2015. Exclusion criteria included use of an ablation antenna other than the Precision (PR) or Lung (LN) antenna. Ablation

Ablation Work

Ablation procedures were performed using the NeuWave Certus PR (n = 59) or LN (n = 39) antenna, with single antenna microwave ablation (n = 82) or simultaneous microwave ablation using 2 (n = 15) or 3 (n = 1) antennas. Mean ablation work for all ablations was 41.3 kJ ± 21.3 (range, 9–117 kJ). There was a significant correlation of ablation work with ablation zone on CT after the procedure (P < .001, r = .633), at 1–3 months (P < .001, r = .620), and at 3–12 months (P < .05, r = .249). There was

Discussion

Analysis of 98 pulmonary tumor ablations with a single microwave ablation system demonstrates a correlation of pulmonary ablation work with ablation zone on imaging during the first year. Given lack of correlation between ablation times with ablation zone, the ablation work correlation is predominantly driven by the selection of ablation power. However, use of work as a reference allows simultaneous quantification and standardization of ablation power and time in the setting of multiple

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Cited by (21)

Safety and Efficacy Outcomes From a Single-Center Study of Image-Guided Percutaneous Microwave Ablation for Primary and Metastatic Lung Malignancy
2023, JTO Clinical and Research Reports
Image-guided percutaneous microwave ablation (MWA) is becoming a more common treatment option for patients with primary and metastatic lung malignancies. Nevertheless, there is limited literature on the safety and efficacy of MWA compared with standard-of-care therapy, including surgical resection and radiation. This study will report the long-term outcomes after MWA for pulmonary malignancies and investigate the factors related to efficacy, including lesion size, location, and ablation power.
Retrospective single-center study analyzing 93 patients who underwent percutaneous MWA for primary or metastatic lung malignancies. Outcomes included immediate technical success, local tumor recurrence, overall survival, disease-specific survival, and complications.
At a single institution, 190 lesions (81 primary and 109 metastatic) were treated in 93 patients. Immediate technical success was achieved in all cases. Freedom from local recurrence was 87.6%, 75.3%, and 69.2% and overall survival was 87.7%, 76.2%, and 74.3% at 1 year, 2 years, and 3 years, respectively. Disease-specific survival was 92.6%, 81.8%, and 81.8%. The most common complication was pneumothorax, which occurred in 54.7% (104 of 190) of procedures, with 35.2% (67 of 190) requiring a chest tube. No life-threatening complications occurred.
Percutaneous MWA seems safe and effective for treatment of primary and metastatic lung malignancies and should be considered for patients with limited metastatic burden and lesions less than 3 cm in size.
Society of Interventional Radiology Quality Improvement Standards on Percutaneous Ablation of Non–Small Cell Lung Cancer and Metastatic Disease to the Lungs
2021, Journal of Vascular and Interventional Radiology
Citation Excerpt :
MWA appears to have the ability to overcome some effects of thermal sinks and may be the preferred modality in this context. There is evidence that the location of the targeted tumor has an influence on the size of the ablation zone, with centrally located tumors in the lower lobes having the highest ablation resistance score (40). Tumor size is a factor that warrants consideration when choosing an ablation modality.
To provide guidance on quality improvement thresholds for outcomes and complications of image-guided thermal ablation for the treatment of early stage non-small cell lung cancer, recurrent lung cancer, and metastatic disease.
A multidisciplinary writing group conducted a comprehensive literature search to identify studies on the topic of interest. Data were extracted from relevant studies and thresholds were derived from a calculation of 2 standard deviations from the weighted mean of each outcome. A modified Delphi technique was used to achieve consensus agreement on the thresholds.
Data from 29 studies, including systematic reviews and meta-analyses, retrospective cohort studies, and single-arm trials were extracted for calculation of the thresholds. The expert writing group agreed on thresholds for local control, overall survival and adverse events associated with image-guided thermal ablation.
SIR recommends utilizing the indicator thresholds to review and assess the efficacy of ongoing quality improvement programs. When performance falls above or below specific thresholds, consideration of a review of policies and procedures to assess for potential causes, and to implement changes in practices, may be warranted.
Relationship of Antenna Work and Ablation Cavity Volume Following Percutaneous Microwave Ablation of Hepatic Tumors
2021, Journal of Vascular and Interventional Radiology
Citation Excerpt :
Volumes were calculated using the following ellipsoid volume formula (4/3 × π × r1 × r2 × r3), where r is the dimensional radius. Antenna work was calculated based on the following formula, as described by Al-Hakim et al (6): Antenna work (Joules) = Power of ablation (Watts) × duration of ablation (seconds).
To formulate a statistical model relating ablation time, power, and work with posttreatment cavity volume following percutaneous microwave ablation of hepatic tumors in vivo.
A retrospective review (October 2015 to October 2018) yielded 122 hepatic tumors treated with microwave ablation. Ablation cavity dimensions were measured at 1-month follow-up examination and calculated using an ellipsoid volume formula. The antenna manufacturer (Neuwave Medical, Madison, Wisconsin) provided the activation time and energy used to calculate the antenna work. Generalized estimating equations with ordinary least-squares regression models were obtained to relate tumor volume with cumulative antenna work. Coefficient of determination (R²) and mean square error were used as statistical measures of model prediction performance.
There is a logarithmic relationship between postablation cavity volume (cm³) and cumulative work (kJ), represented by the formula: log₁₀ cm³ = −0.4583 + 0.9887 × cumulative work (log10 kJ) (R² = 0.41, mean square error, 0.102). Ablation volumes were predicted as a function of antenna work, calculated using an antilog transformation. When a single antenna was used, ablation cavity volume was predicted using a generalized estimating equation ordinary least-squares regression model of power and time: log₁₀cm³= −0.0546 + 0.0485 × total time (min) + 0.0107 × power (W) (R² = 0.30; mean square error, 0.106). Using this model, a nomogram was developed to predict the postablation cavity volume based on total activation time and target power.
There is a logarithmic relationship between the ablation work and posttreatment ablation cavity volume, which can be expressed in a nomogram when using a single probe.
Alternatives to Surgery for Early-Stage Non–Small Cell Lung Cancer: Thermal Ablation
2020, Clinics in Chest Medicine
Citation Excerpt :
Likewise, cryoablation is vulnerable to cold-sink effects, and probe placement adjacent to a vascular structure can result in inhomogeneous temperatures and increased risk for local failure.8 Location within the lung has also been found to influence the size of the ablation zone, with upper lobes and peripheral locations allowing larger ablation zones than lower lobes and central locations, possibly related to differences in tissue perfusion.9 Extrapulmonary structures at risk for damage must always be considered when planning the ablation procedure, particularly for tumors in peripheral locations within the lung lobe but central within the chest.
In vivo percutaneous microwave ablation in kidneys: Correlation with ex vivo data and ablation work
2018, Diagnostic and Interventional Imaging
Citation Excerpt :
This observation was made either with 1 or 2 antennas. These results are consistent with the literature as studies on the liver and lung showed that in vivo ablation zones were smaller than the ex vivo ablation areas [8,10,13]. Similarly, the area of necrosis was smaller than the expected area after laparoscopic renal ablation [20].
To compare diameters of in vivo microwave ablation (MWA) performed in swine kidneys with ex vivo diameters, and to correlate with ablation work (AW), a new metric reflecting total energy delivered.
Eighteen in vivo MWA were performed in 6 swine kidneys successively using one or two antennas (MicroThermX^®). Ablation consisted in delivering power (45–120 W) for 5–15 minutes. Ex vivo diameters were provided by the vendors and obtained on bovine liver tissue. AW was defined as the sum of (power)*(time)*(number of antennas) for all phases of an ablation (in kJoules). Kidneys were removed laparoscopically immediately after ablation. After sacrifice, ablations zones were evaluated macroscopically, and maximum diameters of the zones were recorded. Wilcoxon sum rank test and Pearson's correlation were used for comparisons.
For a single antenna (n = 12), the in vivo diameters ranged from 12 to 35 mm, and 15–49 mm for 2 antennas (n = 6). The in vivo diameters remained shorter than ex vivo diameters by 8.6% ± 30.1 on 1 antenna and 11.7% ± 26.5 on 2 antennas (P = 0.31 and 0.44, respectively). AW ranged from 13.5 to 108 kJ. Diameters increased linearly with AW both with 1 and 2 antennas, but only moderate correlations were observed (r = 0.43 [95% confidence interval: −0.19; 0.81], P = 0.16; and 0.57 [−0.44; 0.95], P = 0.24, respectively).
Although diameters after in vivo renal MWA increased linearly with AW, the moderate correlation and wide standard deviations observed may justify a careful imaging monitoring during treatment delivery and settings adaptation, if needed, for optimal ablation.
Microwave ablation of renal tumors: A narrative review of technical considerations and clinical results
2017, Diagnostic and Interventional Imaging
Citation Excerpt :
While correlations with MW settings such as power and time and CEM43 have to be performed, these results suggest that adequate renal MWA leads to increase time and/or power in order to reach CEM43 > 70 min and to observe consistent tissue damage. Authors have recently proposed new quantitative measures, such as “ablation work” and “ablation resistance score” in treated lung tumors to better analyze thermal ablation zones and to improve treatments in this complex and heterogeneous patient population and tissue environment [24,25]. By measuring the total amount of work as a summation of applicator power and time product over different phases of the ablation, the “ablation work” may help to standardize the ablation zone calculation and to improve the understanding of the effects of tissue type, tissue perfusion, adjacent heat sinks, and dielectrical effects and how all of these affect the specific absorption rate of microwave energy during thermal ablation [25].
The purpose of this review was to identify the specific technical considerations to adequately perform microwave ablations (MWA) of renal tumors and analyze the currently available clinical results.
Using Medline, a systematic review was performed including articles published between January 2000 and September 2016. English language original articles, reviews and editorials were selected based on their clinical relevance.
MWA has several theoretical advantages over radiofrequency ablation in consistently providing higher intratumoral temperatures. MWA is less dependent of electrical conductivities of tissues and the delivered energy is less limited by desiccation of heated tissues. While there are insufficient data, especially because of a lack of studies with mid- to long-term follow-up, to determine the oncologic effectiveness of MWA, this technique appears safe and effective for the ablation of T1 renal tumors. There is evidence for using mid-level settings based on experimental and clinical data. Power set at 50–65 W for 5–15 min appears adequate in kidney but close clinical and imaging follow-up have to be performed.
Renal MWA offers theoretical advantages by comparison with other available techniques to treat renal tumors. However, MWA suffers of less cumulative data compared to radiofrequency ablation or cryoablation. Moreover, microwaves still require further studies to identify the optimal tumor characteristics and device settings leading to predictable ablation.

View all citing articles on Scopus

: F.G.A. is a paid consultant for HealthTronics, Inc (Austin, Texas) and participated in a clinical trial for Galil Medical, Inc (Arden Hills, Minnesota). R.D.S. is a paid consultant for NeuWave Medical, Inc (Madison, Wisconsin) and HealthTronics, Inc, receives grants from HealthTronics, Inc, and performed research for Galil Medical, Inc. None of the other authors have identified a conflict of interest.

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Clinical StudyDefining New Metrics in Microwave Ablation of Pulmonary Tumors: Ablation Work and Ablation Resistance Score

Abstract

Purpose

Materials and Methods

Results

Conclusions

Section snippets

Materials and Methods

Ablation Work

Discussion

J Vasc Interv Radiol

J Surg Res

Tech Vasc Interv Radiol

J Vasc Interv Radiol

Surg Oncol Clin N Am

Curr Probl Diagn Radiol

Pulmonary thermal ablation: comparison of radiofrequency and microwave devices by using gross pathologic and CT findings in a swine model

Radiology

Microwave ablation of lung malignancies: effectiveness, CT findings, and safety in 50 patients

Radiology

Effect of vessel size on creation of hepatic radiofrequency lesions in pigs: assessment of the “heat sink” effect

AJR Am J Roentgenol

Image-guided tumor ablation: standardization of terminology and reporting criteria—a 10-year update

J Vasc Interv Radiol

Radiofrequency ablation of lung metastases: factors influencing success

Eur Radiol

Society of Interventional Radiology Technology Assessment Committee; International Working Group on Image-Guided Tumor Ablation. Image-guided tumor ablation: standardization of terminology and reporting criteria

Radiology

Radiofrequency versus microwave ablation in a hepatic porcine model

Radiology

Clinical Study
Defining New Metrics in Microwave Ablation of Pulmonary Tumors: Ablation Work and Ablation Resistance Score