Safety margin assessment after microwave ablation of liver tumors: inter- and intrareader variability

Abstract

BackgroundThe aim of the study was to evaluate the inter- and intrareader variability of the safety margin assessment after microwave ablation of liver tumors using post-procedure computed tomography (CT) images as well as to determine the sensitivity and specificity of identification remnant tumor tissue.Patients and methodsA retrospective analysis of 58 patients who underwent microwave ablation (MWA) of primary or secondary liver malignancies (46 hepatocellular carcinoma, 9 metastases of a colorectal cancer and 3 metastases of pancreatic cancer) between September 2017 and June 2019 was conducted. Three readers estimated the minimal safety margin in millimeters using side-by-side comparison of the 1-day pre-ablation CT and 1-day post-ablation CT and judged whether ablation was complete or incomplete. One reader estimated the safety margin again after 6 weeks. Magnetic resonance imaging (MRI) after 6 weeks was the gold standard.ResultsThe intraclass correlation coefficient (ICC) for estimation of the minimal safety margin of all three readers was 0.357 (95%-confidence interval 0.194–0.522). The ICC for repeated assessment (reader 1) was 0.774 (95%-confidence interval 0.645–0.860). Sensitivity and specificity of the detection of complete tumor ablation, defined as no remnant tumor tissue in 6 weeks follow-up MRI, were 93%/82%/82% and 33%/17%/83%, respectively.ConclusionsIn clinical practice, the safety margin after liver tumor ablation is often assessed using side-by-side comparison of CT images. In the study, we were able to show, that this technique has a poor reliability (ICC 0.357). From our point of view, this proves the necessity of new technical procedures for the assessment of the safety distance.

Volumetric Quantitative Ablation Margins for Assessment of Ablation Completeness in Thermal Ablation of Liver Tumors

“…Contrarily, in image-guided thermal ablation the assessment of treatment completeness is mainly performed by visual inspection of follow-up imaging. Even though a correspondence between radiologic and histopathologic findings in explanted livers was reported after radiofrequency ablation of hepatocellular carcinoma ( 29 ), a visual assessment without available histopathology results remains subjective and prone to inter-personal variations ( 13 ).…”

“…At present, the ablation margin is most commonly assessed visually, either using side-by-side juxtaposition of pre- and post-ablation images or using image-fusion, and reported in 2D at the site of largest tumor diameter ( 3 , 4 , 6 , 12 ). The disadvantages of such evaluation include an accuracy limited to one 2D image, which is prone to subjectivity and inter-reader variability, even when performed by experienced radiologists ( 13 ).…”

“…Firstly, the description of circumferential ablation margins for tumors in close vicinity to the liver capsule cannot be accomplished due to the inherently limited surrounding liver parenchyma. These cases are rarely addressed in the literature ( 12 , 13 ), and no detailed technical solution for the computation of QAM for subcapsular tumors exists to date. Secondly, most studies focus on an average minimal ablation margin, whereas the assessment of a quantitative distribution of margin distances could take the accuracy of QAM one step further.…”

Assessing ablation margins of FDG-avid liver tumors during PET/CT-guided thermal ablation procedures: a retrospective study

“…b CT shows the final ablation zone ice ball (arrows) within which the tumor is obscured and c fused PET/CT allows visualization of the tumor and measurement of the ablation margin (asterisk) thickness, demonstrating an adequate ablation margin circumferentially. The minimum margin measured 5.5 mm postprocedure images, an approach that is not always feasible, may be time-consuming, and has poor interobserver agreement [5,24]. Consequently, retrospective image fusion techniques are increasingly proposed, despite a dependence on retrospective tumor images and susceptibility to misregistration or anatomic deformations caused by instrument insertions, hydro-dissection/artificial ascites, tissue/tumor contraction, gas formation, hematomas, and respiratory or positional variations [11][12][13].…”

Improvement of the primary efficacy of microwave ablation of malignant liver tumors by using a robotic navigation system

“…are still no uniform guidelines for the minimum safety margin (distance between treated tumor and ablation margin), most operators assume a safety margin of approximately 0.5–1 cm. 11 , 12 , 13 To achieve this, the microwave applicator (antenna) must be positioned with millimeter precision, which can be very challenging, especially in the case of several overlapping ablation areas. In addition to the common freehand placement, modern navigation systems have been introduced to allow 3D planning and precise antenna placement.…”