Radiofrequency ablation of liver metastases-software-assisted evaluation of the ablation zone in MDCT: tumor-free follow-up versus local recurrent disease

Evaluation of the Ki-67 labeling index on immediate pre-ablation biopsies as a predictive biomarker of local recurrence of colorectal cancer liver metastases

The aim of this study was to evaluate if the Ki-67 labeling index (LI) on immediate pre-ablation biopsies of colorectal liver metastases (CLM) is associated with the presence of viable tumor cells in subsequent ablation zone biopsies and/or local tumor progression-free survival (LTPFS). Biopsies of CLM were performed before and after microwave ablation (MWA), as part of a prospective clinical trial between October 2013 and May 2019. Pre-ablation biopsy slides were examined for the Ki-67 LI using light microscopy. Ablation zone biopsy specimens were evaluated for the presence of viable tumor using hematoxylin-eosin and immunohistochemistry. Differences in CLM Ki-67 LI between positive and negative for viable tumor ablation zone biopsies were assessed using the Mann-Whitney U test. Biopsy, tumor and margin data were evaluated as predictors of LTPFS using Kaplan-Meier/Cox methods. Thirty-four patients with 48 CLM underwent biopsy before and after MWA. Sufficient tissue for Ki-67 labeling was obtained in 43/48 (89.6%) CLM. Viable tumor cells were detected in 11 ablation zones (22.9%). There was no significant difference in the CLM Ki-67 LI between the positive and negative for viable tumor ablation zones (mean: 69.2% vs. 64.3% respectively, p = 0.4). Adequate ablation zone margins (> 5 mm; p = 0.029) and negative ablation zone biopsies (p = 0.009) were significant predictors of longer LTPFS. KRAS status, tumor size and Ki-67 LI were not significant predictors of LTPFS. Complete tumor ablation (with adequate margins and negative ablation zone biopsies) is the most important factor in achieving local control of CLM, even for tumors exhibiting aggressive tumor biology.

Ablation margin quantification after thermal ablation of malignant liver tumors: How to optimize the procedure? A systematic review of the available evidence

Introduction

To minimize the risk of local tumor progression after thermal ablation of liver malignancies, complete tumor ablation with sufficient ablation margins is a prerequisite. This has resulted in ablation margin quantification to become a rapidly evolving field. The aim of this systematic review is to give an overview of the available literature with respect to clinical studies and technical aspects potentially influencing the interpretation and evaluation of ablation margins.

Methods

The Medline database was reviewed for studies on radiofrequency and microwave ablation of liver cancer, ablation margins, image processing and tissue shrinkage. Studies included in this systematic review were analyzed for qualitative and quantitative assessment methods of ablation margins, segmentation and co-registration methods, and the potential influence of tissue shrinkage occurring during thermal ablation.

Results

75 articles were included of which 58 were clinical studies. In most clinical studies the aimed minimal ablation margin (MAM) was ≥ 5 mm. In 10/31 studies, MAM quantification was performed in 3D rather than in three orthogonal image planes. Segmentations were performed either semi-automatically or manually. Rigid and non-rigid co-registration algorithms were used about as often. Tissue shrinkage rates ranged from 7% to 74%.

Conclusions

There is a high variability in ablation margin quantification methods. Prospectively obtained data and a validated robust workflow are needed to better understand the clinical value. Interpretation of quantified ablation margins may be influenced by tissue shrinkage, as this may cause underestimation.

Real-Time Split-Dose PET/CT-Guided Ablation Improves Colorectal Liver Metastasis Detection and Ablation Zone Margin Assessments without the Need for Repeated Contrast Injection

BACKGROUND

Real-time split-dose PET can identify the targeted colorectal liver metastasis (CLM) and eliminate the need for repeated contrast administration before and during thermal ablation (TA). This study aimed to assess the added value of pre-ablation real-time split-dose PET when combined with non-contract CT in the detection of CLM for ablation and the evaluation of the ablation zone and margins.

METHODS

A total of 190 CLMs/125 participants from two IRB-approved prospective clinical trials using PET/CT-guided TA were analyzed. Based on detection on pre-TA imaging, CLMs were categorized as detectable, non-detectable, and of poor conspicuity on CT alone, and detectable, non-detectable, and low FDG-avidity on PET/CT after the initial dose. Ablation margins around the targeted CLM were evaluated using a 3D volumetric approach.

RESULTS

We found that 129/190 (67.9%) CLMs were detectable on CT alone, and 61/190 CLMs (32.1%) were undetectable or of poor conspicuity, not allowing accurate depiction and targeting by CT alone. Thus, the theoretical 5- and 10-mm margins could not be defined in these tumors (32.1%) using CT alone. When TA intraprocedural PET/CT images are obtained and inspected (fused PET/CT), only 4 CLM (2.1%) remained undetectable or had a low FDG avidity.

CONCLUSIONS

The addition of PET to non-contrast CT improved CLM detection for ablation targeting, margin assessments, and continuous depiction of the FDG avid CLMs during the ablation without the need for multiple intravenous contrast injections pre- and intra-procedurally.

Local tumour control after radiofrequency or microwave ablation for colorectal liver metastases in relation to histopathological growth patterns

BACKGROUND

Regrowth after ablation is common, but predictive factors for local control are scarce. This study investigates whether histopathological growth patterns (HGP) can be used as a predictive biomarker for local control after ablation of colorectal liver metastases (CRLM).

METHODS

Patients who received simultaneous resection and ablation as first treatment for CRLM between 2000 and 2019 were considered eligible. HGPs were determined on resected CRLM according to international guidelines and were classified as desmoplastic or non-desmoplastic. As minimal inter-tumoural heterogeneity has been demonstrated, the HGP of resected and ablated CRLM were presumed to be identical. Local tumour progression (LTP) was assessed on postoperative surveillance imaging. Uni- and multivariable competing risk methods were used to compare LTP.

RESULTS

In total 221 patients with 443 ablated tumours were analysed. A desmoplastic HGP was found in 60 (27.1%) patients who had a total of 159 (34.7%) ablated lesions. Five-year LTP [95%CI] was significantly higher for ablated CRLM with a presumed non-desmoplastic HGP (37% [30-43] vs 24% [17-32], Gray's-test p = 0.014). On multivariable analysis, a non-desmoplastic HGP (adjusted HR [95%CI]; 1.55 [1.03-2.35]) was independently associated with higher LTP rates after ablation.

CONCLUSION

HGP is an independent predictor of local tumour progression following ablation of CRLM.

Biopsy and Margins Optimize Outcomes after Thermal Ablation of Colorectal Liver Metastases

Simple Summary

Thermal ablation (TA) is a non-surgical treatment of cancer that has been used with success in the treatment of colorectal liver metastases (CLM). TA consists of burning the cancer and a rim of surrounding tissue (margin) with a special needle placed in the tumor under image guidance. Despite the technological evolution of TA, tumor progression/recurrence rates remain higher than expected. We present a method that combines tissue and imaging tests performed immediately after ablation to determine whether there is complete tumor destruction or remaining live cancer cells that can cause tumor progression/recurrence. This information can provide guidance for additional treatments for patients with evidence of residual cancer, i.e.,: additional TA at the same or subsequent sitting, or additional chemotherapy and short-interval imaging follow-up to detect recurrence. The presented method proposes a clinical practice paradigm change that can improve clinical outcomes in a large population of patients with CLM treated by TA.

Abstract

Background: Thermal ablation is a definitive local treatment for selected colorectal liver metastases (CLM) that can be ablated with adequate margins. A critical limitation has been local tumor progression (LTP). Methods: This prospective, single-group, phase 2 study enrolled patients with CLM < 5 cm in maximum diameter, at a tertiary cancer center between November 2009 and February 2019. Biopsy of the ablation zone center and margin was performed immediately after ablation. Viable tumor in tissue biopsy and ablation margins < 5 mm were assessed as predictors of 12-month LTP. Results: We enrolled 107 patients with 182 CLMs. Mean tumor size was 2.0 (range, 0.6–4.6) cm. Microwave ablation was used in 51% and radiofrequency ablation in 49% of tumors. The 12- and 24-month cumulative incidence of LTP was 22% (95% confidence interval [CI]: 17, 29) and 29% (95% CI: 23, 36), respectively. LTP at 12 months was 7% (95% CI: 3, 14) for the biopsy tumor-negative ablation zone with margins ≥ 5 mm vs. 63% (95% CI: 35, 85) for the biopsy-positive ablation zone with margins < 5 mm (p < 0.001). Conclusions: Biopsy-proven complete tumor ablation with margins of at least 5 mm achieves optimal local tumor control for CLM, regardless of the ablation modality used.

3D margin assessment predicts local tumor progression after ablation of colorectal cancer liver metastases

OBJECTIVE

To determine the feasibility and prognostic value of 3D measuring of the ablation margins using a dedicated image registration software.

METHODS

This retrospective study included 104 colorectal liver metastases in 68 consecutive patients that underwent microwave ablation between 08/2012 and 08/2019. The minimal ablation margin (MM) was measured in 2D using anatomic landmarks on contrast enhanced CT(CECT) 4-8 weeks post-ablation, and in 3D using an image registration software and immediate post-ablation CECT. Local tumor progression (LTP) was assessed by imaging up to 24 months after ablation. A blinded interventional radiologist provided feedback on the possibility of additional ablation after examining the 3D-margin measurements.

RESULTS

The 3D-margin assessment was completed in 79/104 (76%) tumors without the need for target manipulation. In 25/104 (24%) tumors, manipulation was required due to image misregistration. LTP was observed in 40/104 (38.5%) tumors: 92.5% vs 7.5% for those with margin <5mm vs ≥5mm, respectively (p = 0.0001). The 2D and 3D-assessments identified margin <5mm in 17/104 (16%), and in 74/104 (71%) ablated tumors, respectively (p < 0.01). The sensitivity and specificity of the 3D software for predicting LTP was 93% (37/40) and 42% (27/64), respectively. Additional ablation to achieve a MM of 5 mm would have been offered in 26/37 cases if the 3D-margin assessment was available intraoperatively.

CONCLUSION

Image registration software can measure ablation margins and detect MM under 5 mm intraoperatively, with significantly higher sensitivity than the 2D technique using landmarks on the post-ablation CECT. The identification of a margin under 5 mm is strongly associated with LTP.

Local Treatments in the Unresectable Patient with Colorectal Cancer Metastasis: A Review from the Point of View of the Medical Oncologist

For patients with isolated liver metastases from colorectal cancer who are not candidates for potentially curative resections, non-surgical local treatments may be useful. Non-surgical local treatments are classified according to how the treatment is administered. Local treatments are applied directly on hepatic parenchyma, such as radiofrequency, microwave hyperthermia and cryotherapy. Locoregional therapies are delivered through the hepatic artery, such as chemoinfusion, chemoembolization or selective internal radiation with Yttrium 90 radioembolization. The purpose of this review is to describe the different interventional therapies that are available for these patients in routine clinical practice, the most important clinical trials that have tried to demonstrate the effectiveness of each therapy and recommendations from principal medical oncologic societies.

Repeat Local Treatment of Recurrent Colorectal Liver Metastases, the Role of Neoadjuvant Chemotherapy: An Amsterdam Colorectal Liver Met Registry (AmCORE) Based Study

This cohort study aimed to evaluate efficacy, safety, and survival outcomes of neoadjuvant chemotherapy (NAC) followed by repeat local treatment compared to upfront repeat local treatment of recurrent colorectal liver metastases (CRLM). A total of 152 patients with 267 tumors from the prospective Amsterdam Colorectal Liver Met Registry (AmCORE) met the inclusion criteria. Two cohorts of patients with recurrent CRLM were compared: patients who received chemotherapy prior to repeat local treatment (32 patients) versus upfront repeat local treatment (120 patients). Data from May 2002 to December 2020 were collected. Results on the primary endpoint overall survival (OS) and secondary endpoints local tumor progression-free survival (LTPFS) and distant progression-free survival (DPFS) were reviewed using the Kaplan-Meier method. Subsequently, uni- and multivariable Cox proportional hazard regression models, accounting for potential confounders, were estimated. Additionally, subgroup analyses, according to patient, initial and repeat local treatment characteristics, were conducted. Procedure-related complications and length of hospital stay were compared using chi-square test and Fisher's exact test. The 1-, 3-, and 5-year OS from date of diagnosis of recurrent disease was 98.6%, 72.5%, and 47.7% for both cohorts combined. The crude survival analysis did not reveal a significant difference in OS between the two cohorts (p = 0.834), with 1-, 3-, and 5-year OS of 100.0%, 73.2%, and 57.5% for the NAC group and 98.2%, 72.3%, and 45.3% for the upfront repeat local treatment group, respectively. After adjusting for two confounders, comorbidities (p = 0.010) and primary tumor location (p = 0.023), the corrected HR in multivariable analysis was 0.839 (95% CI, 0.416-1.691; p = 0.624). No differences between the two cohorts were found with regards to LTPFS (HR = 0.662; 95% CI, 0.249-1.756; p = 0.407) and DPFS (HR = 0.798; 95% CI, 0.483-1.318; p = 0.378). No heterogeneous treatment effects were detected in subgroup analyses according to patient, disease, and treatment characteristics. No significant difference was found in periprocedural complications (p = 0.843) and median length of hospital stay (p = 0.600) between the two cohorts. Chemotherapy-related toxicity was reported in 46.7% of patients. Adding NAC prior to repeat local treatment did not improve OS, LTPFS, or DPFS, nor did it affect periprocedural morbidity or length of hospital stay. The results of this comparative assessment do not substantiate the routine use of NAC prior to repeat local treatment of CRLM. Because the exact role of NAC (in different subgroups) remains inconclusive, we are currently designing a phase III randomized controlled trial (RCT), COLLISION RELAPSE trial, directly comparing upfront repeat local treatment (control) to neoadjuvant systemic therapy followed by repeat local treatment (intervention).

Microwave ablation for colorectal cancer metastasis to the liver: a single-center retrospective analysis

Background

The purpose of this study is to evaluate the safety and intermediate-term efficacy of percutaneous microwave (MW) ablation for the treatment of colorectal liver metastases (CRLM) at a single institution.

Methods

A retrospective review was performed of all CRLM treated with MW ablation from 3/2011 to 7/2020 (102 tumors; 72 procedures; 57 patients). Mean age was 60 years (range, 36-88) and mean tumor size was 1.8 cm (range, 0.5-5.0 cm). The patient population included 19 patients with extra-hepatic disease. Chemotherapy (pre- and/or post-ablation) was given in 98% of patients. Forty-five sessions were preceded by other focal CRLM treatments including resection, ablation, radiation, and radioembolization. Kaplan-Meier curves were used to estimate local tumor progression-free survival (LTPFS), disease-free survival (DFS), and overall survival (OS) and multivariate analysis (Cox Proportional Hazards model) was used to test predictors of OS.

Results

Technical success (complete ablation) was 100% and median follow-up was 42 months (range, 1-112). There was a 4% major complication rate and an overall complication rate of 8%. Local tumor progression (LTP) rate during the entire study period was 4/98 (4%), in which 2 were retreated with MW ablation for a secondary LTP-rate of 2%. LTP-free survival at 1, 3, and 5 years was 93%, 58%, and 39% and median LTP-free survival was 48 months. OS at 1, 3, and 5 years was 96%, 66%, 47% and median OS was 52 months. There were no statistically significant predictors of OS.

Conclusions

MW ablation of hepatic colorectal liver metastases appears safe with excellent local tumor control and prolonged survival compared to historical controls in selected patients. Further comparative studies with other local treatment strategies appear indicated.

Percutaneous lung and liver CT-guided ablation on swine model using microwave ablation to determine ablation size for clinical practice

PURPOSE

Microwave ablation (MWA) provides an effective treatment of lung and liver tumors but suffers from a lack of reproducibility of ablation size among currently available technologies. In-vitro evaluations are far removed from clinical practices because of uninfused tissue. This study is in-vivo preclinical testing of a new MWA system on swine lungs and liver.

MATERIALS AND METHODS

All ablations were performed under CT guidance and multiple algorithms were tested with a power of 50, 75, and 100 W for durations of 3, 5, 8, 10, and 15 min. A 3 D-evaluation of the ablation zone was carried out using enhanced-CT. The sphericity index, coefficients of variation, and energy efficiency (which corresponds to the volume yield according to the power supplied) were calculated.

RESULTS

Fifty liver and 48 lung ablations were performed in 17 swine. The sphericity index varies from 0.50 to 0.80 for liver ablations and from 0.40 to 0.69 for lung ablations. The coefficient of variation was below 15% for 4/5 and 4/8 protocols for lung and liver ablations, respectively. The energy efficiency seems to decrease with the duration of the ablation from 0.60 × 10^-3 cm³/J (75 W, 3 min) to 0.26 × 10^-3 cm³/J (100 W, 15 min) in the liver and from 0.57 × 10^-3 cm³/J (50 W, 10 min) to 0.42 × 10^-3 cm³/J (100 W, 12 min) in the lungs.

CONCLUSION

A shorter treatment time provides the best energy efficiency, and the best reproducibility is obtained for a 10 min treatment duration. The system tested provides an interesting reproducibility in both lung and liver measurements. Our results may help interventional radiologists in the optimal selection of treatment parameters.

Comparison of Chronologic Change in the Size and Contrast-Enhancement of Ablation Zones on CT Images after Irreversible Electroporation and Radiofrequency Ablation

Objective

To compare short-, mid-, and long-term follow-up ablation zone volume alterations as well as imaging features on contrast-enhanced computed tomography (CT) after irreversible electroporation (IRE) of primary and secondary liver tumors with findings subsequent to radiofrequency ablation (RFA).

Materials and Methods

Volume assessment of 39 ablation zones (19 RFA, 20 IRE) after intervention was performed at four time intervals (day 0 [t1; n = 39], day 1-7 [t2; n = 25], day 8-55 [t3; n = 28], after day 55 [t4; n = 23]) on dual-phase CT. Analysis of peripheral rim enhancement was conducted. Lesion's volume decrease relative to the volume at t1 was calculated and statistically analyzed with respect to patient's sex, age, ablation modality (IRE/RFA), and history of platinum-based chemotherapy (PCT).

Results

No influence of patient's sex or age on ablation volume was detected. The decrease in ablation zones' volume was significantly larger (p < 0.05 for all time intervals) after IRE (arterial phase, 7.5%; venous phase, 9.7% of initial volume) compared to RFA (arterial phase, 39.6%; venous phase, 45.3% of initial volume). After RFA, significantly smaller decreases in the ablation volumes, in general, were detected in patients treated with PCT in their history (p = 0.004), which was not detected after IRE (p = 0.288). In the arterial phase, peripheral rim enhancement was frequently detected after both IRE and RFA. In the venous phase, rim-enhancement was depicted significantly more often following IRE at t1 and t2 (pt1 = 0.003, pt2 < 0.001).

Conclusion

As per our analysis, ablation zone volume decreased significantly in a more rapid and more profound manner after IRE. Lesion's remodeling after RFA but not IRE seems to be influenced by PCT, possibly due to the type of cell death induced by the different ablation modalities.

Morphometric and chronological behavior of 2.45 GHz microwave ablation zones for colorectal cancer metastases and hepatocellular carcinoma in the liver: preliminary report

BACKGROUND

Percutaneous microwave ablation (MWA) is increasingly utilized in the treatment of primary and secondary hepatic malignancy. As an in-situ treatment appreciation of any signs of recurrence is critical for improving long-term oncological outcomes. Volumetry has been recognized as having advantages over orthogonal measurements in the response assessment of malignant lesions. Our study set out to look at the normal involution of an ablation zone (AZ) both volumetrically and morphologically to see if this information might aid the detection of local tumor progression.

METHODS

Cases were identified retrospectively from our database of liver MWA. We identified 34 AZs in total, 18 AZs in 16 hepatocellular carcinoma (HCC) patients with cirrhosis on imaging grounds and 13 AZs in patients with metastatic colorectal cancer. How these AZs developed over time was analyzed both morphologically and quantitatively using Siemens Syngo Via post-processing software. We used the software to produce volume measurements and short axis orthogonal measurements. A baseline measurement was taken on the first <30 day post-ablation scan and the chronological changes were then plotted.

RESULTS

We saw differences between the cirrhotic and non-cirrhotic patients both in terms of morphological and volumetric changes. 12/13 non-cirrhotic AZs had a volume of <50% of the baseline scan within the first year. The cirrhotic patients were less predictable, but 14/18 still shrunk to less than 50% of baseline volume in the first year. Orthogonal measurements were less useful in both groups. Qualitatively, there was initially a slightly less well-defined border to the AZ in the first 3 months, which became better defined over time and certainly over the first year of AZ involution.

CONCLUSION

Volumetric analysis is a useful adjunct to conventional measurements and qualitative analysis of AZs. This can be reassuring when orthogonal measurements are static or difficult to interpret. Our preliminary data suggest that the normal pattern in a non-cirrhotic liver is that the AZ volume should drop below 50% of baseline at 1 year. Volumes in cirrhotic livers are less predictable, but the majority will still follow a similar pattern. Future studies could evaluate if failure to follow these patterns correlates with local tumor progression.

Volumetric evaluation of hepatic tumors: multi-vendor, multi-reader liver phantom study

PURPOSE

To compare liver lesion volume measurement on multiple 3D software platforms using a liver phantom.

METHODS

An anthropomorphic phantom constructed with ten liver lesions of varying size, attenuation, and shape with known volume and long axis measurement was scanned (120 kVp, 80-440 smart mA, NI 12). DICOM data were uploaded to five commercially available 3D visualization systems and manual tumor volume was obtained by three-independent readers. Accuracy and reproducibility of linear and volume measurements were compared. The two most promising systems were then compared with an additional prototype system by two readers using both manual and semi-automated measurement with similar comparison between linear and volume measures. Measurements were performed on 5- and 1.25-mm data sets. Inter- and intra-observer variability was also assessed.

RESULTS

Overall mean % volume error on the five commercially available software systems (averaging all ten liver lesions among all three readers) was 8.0% ± 7.5%, 13.7% ± 11.2%, 14.2% ± 15.2%, 16.4% ± 14.8 %, and 16.9% ± 13.8%, varying almost twofold across vendor. Moderate inter-observer variability was present. Volume measurement was slightly more accurate than linear measurement, but linear measurement was more reproducible across readers and systems. On the two "best" systems, the manual measurement method was more accurate than the automated method (p = 0.001). The prototype system demonstrated superior semi-automated assessment, with a mean % volume error of 5.3% ± 4.1% (vs. 17.8% ± 11.1% and 31.5% ± 19.7%, p < 0.001), with improved inter- and intra-observer variability.

CONCLUSIONS

Accuracy and reproducibility of volume assessment of liver lesions varies significantly by vendor, which has important implications for clinical use.

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

Image-guided tumor ablation has become a well-established hallmark of local cancer therapy. The breadth of options available in this growing field increases the need for standardization of terminology and reporting criteria to facilitate effective communication of ideas and appropriate comparison among treatments that use different technologies, such as chemical (eg, ethanol or acetic acid) ablation, thermal therapies (eg, radiofrequency, laser, microwave, focused ultrasound, and cryoablation) and newer ablative modalities such as irreversible electroporation. This updated consensus document provides a framework that will facilitate the clearest communication among investigators regarding ablative technologies. An appropriate vehicle is proposed for reporting the various aspects of image-guided ablation therapy including classification of therapies, procedure terms, descriptors of imaging guidance, and terminology for imaging and pathologic findings. Methods are addressed for standardizing reporting of technique, follow-up, complications, and clinical results. As noted in the original document from 2003, adherence to the recommendations will improve the precision of communications in this field, leading to more accurate comparison of technologies and results, and ultimately to improved patient outcomes.

Margin size is an independent predictor of local tumor progression after ablation of colon cancer liver metastases

PURPOSE

This study was designed to evaluate the relationship between the minimal margin size and local tumor progression (LTP) following CT-guided radiofrequency ablation (RFA) of colorectal cancer liver metastases (CLM).

METHODS

An institutional review board-approved, HIPPA-compliant review identified 73 patients with 94 previously untreated CLM that underwent RFA between March 2003 and May 2010, resulting in an ablation zone completely covering the tumor 4-8 weeks after RFA dynamic CT. Comparing the pre- with the post-RFA CT, the minimal margin size was categorized to 0, 1-5, 6-10, and 11-15 mm. Follow-up included CT every 2-4 months. Kaplan-Meier methodology and Cox regression analysis were used to evaluate the effect of the minimal margin size, tumor location, size, and proximity to a vessel on LTP.

RESULTS

Forty-five of 94 (47.9 %) CLM progressed locally. Median LTP-free survival (LPFS) was 16 months. Two-year LPFS rates for ablated CLM with minimal margin of 0, 1-5 mm, 6-10 mm, 11-15 mm were 26, 46, 74, and 80 % (p < 0.011). Minimal margin (p = 0.002) and tumor size (p = 0.028) were independent risk factors for LTP. The risk for LTP decreased by 46 % for each 5-mm increase in minimal margin size, whereas each additional 5-mm increase in tumor size increased the risk of LTP by 22 %.

CONCLUSIONS

An ablation zone with a minimal margin uniformly larger than 5 mm 4-8 weeks postablation CT is associated with the best local tumor control.

Increase in volume of ablation zones during follow-up is highly suggestive of ablation site recurrence in colorectal liver metastases treated with radiofrequency ablation

PURPOSE

To test the hypothesis that volume changes of ablation zones (AZs) on successive computed tomography (CT) scans could predict ablation site recurrences (ASRs) in patients with colorectal liver metastases treated by radiofrequency (RF) ablation.

MATERIALS AND METHODS

RF ablation was performed in 58 patients with 117 metastases. Metastasis volumes and AZ volumes were measured before RF ablation, 1 week after RF ablation (t1), and every 3 months in the first year after RF ablation (t2-t5). Volumetry was performed semiautomatically on CT scans by drawing freehand regions of interest in the portal venous phase on 2-mm-thickness slices. ASR was defined as contrast enhancement on follow-up imaging or by a hot spot on fludeoxyglucose F 18 positron emission tomography combined with computed tomography (FDG-PET/CT) scanning. Proportional volume change of an AZ was defined as the difference in volume percentages between two successive time points of measurement. Negative values represented a volume decrease, and positive values represented a volume increase. Intraobserver variability and interobserver variability were evaluated by using intraclass correlation coefficients (ICCs).

RESULTS

ASRs occurred in 15 patients with 27 AZs. An increase in volume occurred in 26 AZs (96%) with ASRs. AZs without ASR showed no volume increase. Although proportional volume changes at t1-t2 were not predictive for ASR, subsequent volume changes were predictive for ASR. Contrast-enhanced CT-based evaluation detected ASRs in 17 (63%) of 27 AZs, 7 (26%) of 27 AZs were negative, and there was doubt in 3 (11%) of 27 AZs. Intraobserver variability and interobserver variability were good (0.998 [95% confidence interval [CI] 0.996-0.999; P < .001] and 0.993 [95% CI 0.987-0.996; P < .001]).

CONCLUSIONS

Volumetry of AZs is useful because a volume increase of an AZ during follow-up is highly suggestive of ASR. Negative volume changes of the AZ from t1-t2 were not correlated with the development of ASRs, but subsequent volume changes were predictive for ASRs.