Predicting the coagulation volume induced by microwave ablation of hepatocellular carcinoma: the role of deposited energy, ex-vivo bovine liver charts and central hyperdense area on post-treatment CT.

PURPOSE: To study the correlation between the overall coagulation zone (A) attained in percutaneous microwave ablation (MWA) of hepatocellular carcinomas (HCC) and: (1) the hyperdense zone (C) visible in the central part of zone A on post-treatment unenhanced CT scans; (2) the deposited energy; (3) the coagulation zones observed on ex-vivo bovine liver. MATERIALS AND METHODS: The post-procedural computed tomography (CT) scans of HCCs treated with a single energy deployment through the same 2450 MHz MWA system were retrospectively analyzed, retrieving the dimensions of A and C zones and the deposited energy (E). Ex-vivo bovine liver MWA with the same system were performed and analyzed to determine the same quantities by gross-pathologic examination and CT imaging. RESULTS: A total of 101 HCC treatments were analyzed. The average coagulation volumes increased linearly with deposited energy (1.11 cc/kJ, R2 = 0.90, 4.2 kJ ≤ E ≤ 48 kJ), similarly to ex-vivo findings (1.38 cc/kJ, R2 =0.97, 7.2 kJ ≤ E ≤ 144 kJ). The long axis (L) and short axis (D) of zones A and C held a fairly constant ratio both in-vivo (LC/LA=0.43 ± 0.13; DC/DA=0.42 ± 0.10) and ex-vivo (LC/LA = 0.49 ± 0.07; DC/DA = 0.28 ± 0.06). CONCLUSIONS: The average dimensions of the ablation zone induced by the considered system on HCC increase linearly with the deposited energy and are fairly well predicted by the corresponding ex-vivo dimensions. The ratio between each linear dimension of A and C zones was found to be roughly constant over a large deposited energy span, both ex-vivo and in-vivo.

Continuous versus pulsed microwave ablation in the liver: any difference in intraoperative pain scores?

BACKGROUND: This study prospectively compared intraoperative pain scores during percutaneous microwave ablation of the liver in patients randomized between continuous and pulsed energy delivery algorithms. METHODS: During a 12-month period, 20 patients who underwent microwave liver ablation were prospectively randomized between 2 different energy delivery modes: "continuous mode" (CM, n=10) and "pulsed mode" (PM, n=10). All ablation sessions were performed using the same microwave ablation platform under computed tomographic guidance and intravenous analgesia. Within 30 min post ablation, all patients completed a questionnaire assigning a numeric pain intensity score from 0 (no pain) to 10. RESULTS: Mean pain scores were 8.17±1.850 in the CM group and 4.50±1.567 in the PM group, with a statistically significant difference of 3.667±2.807 pain units (P=0.001). The mean procedure time was 53.5±20.90 min in the PM group vs. 58.5±17.44 min in the CM group (P=0.279). The mean size of the lesions was 2.81±0.95 cm in the PM group and 2.81±0.85 cm in the CM group (P=0.984). On a per-lesion basis, technical success was achieved in all evaluable tumors in both groups. No difference was noted in the local tumor control on the 6-month imaging evaluation. No complications were observed in the CM arm, while small perihepatic hemorrhagic fluid collections were reported in the PM group. CONCLUSIONS: Both algorithms for microwave energy delivery have comparable treatment effects in terms of 6-month local tumor control for liver lesions <3 cm in diameter. PM treatments compared to CM appear to induce significantly less pain in patients undergoing percutaneous liver ablation under intravenous analgesia.

Standardizing percutaneous Microwave Ablation in the treatment of Lung Tumors: a prospective multicenter trial (MALT study).

OBJECTIVES: To prospectively assess reproducibility, safety, and efficacy of microwave ablation (MWA) in the treatment of unresectable primary and secondary pulmonary tumors. METHODS: Patients with unresectable primary and metastatic lung tumors up to 4 cm were enrolled in a multicenter prospective clinical trial and underwent CT-guided MWA. Treatments were delivered using pre-defined MW power and duration settings, based on target tumor size and histology classifications. Patients were followed for up to 24 months. Treatment safety, efficacy, and reproducibility were assessed. Ablation volumes were measured at CT scan and compared with ablation volumes obtained on ex vivo bovine liver using equal treatment settings. RESULTS: From September 2015 to September 2017, 69 MWAs were performed in 54 patients, achieving technical success in all cases and treatment completion without deviations from the standardized protocol in 61 procedures (88.4%). Immediate post-MWA CT scans showed ablation dimensions smaller by about 25% than in the ex vivo model; however, a remarkable volumetric increase (40%) of the treated area was observed at 1 month post-ablation. No treatment-related deaths nor complications were recorded. Treatments of equal power and duration yielded fairly reproducible ablation dimensions at 48-h post-MWA scans. In comparison with the ex vivo liver model, in vivo ablation sizes were systematically smaller, by about 25%. Overall LPR was 24.7%, with an average TLP of 8.1 months. OS rates at 12 and 24 months were 98.0% and 71.3%, respectively. CONCLUSIONS: Percutaneous CT-guided MWA is a reproducible, safe, and effective treatment for malignant lung tumors up to 4 cm in size. KEY POINTS: • Percutaneous MWA treatment of primary and secondary lung tumors is a repeatable, safe, and effective therapeutic option. • It provides a fairly reproducible performance on both the long and short axis of the ablation zone. • When using pre-defined treatment duration and power settings according to tumor histology and size, LPR does not increase with increasing tumor size (up to 4 cm) for both primary and metastatic tumors.

Monitoring of Thermal-Induced Changes in Liver Stiffness During Controlled Hyperthermia and Microwave Ablation in an Ex Vivo Bovine Model Using Point Shear Wave Elastography.

PURPOSE: To investigate liver stiffness changes-evaluated by point shear wave elastography (pSWE)-in controlled hyperthermia and microwave ablation (MWA) in an ex vivo animal model. MATERIALS AND METHODS: Five samples of ex vivo bovine liver were uniformly heated to temperatures ranging from 40 to 100 °C. B-mode ultrasound imaging and pSWE were acquired simultaneously, and shear wave velocity (SWV) was measured in a region of interest (ROI). The threshold value of SWV at 60 °C (avg60) was identified. Subsequently, MWA was performed in 11 liver samples at 60 W until avg60 + 0.5 m/s was reached. SWV was measured in ROIs at 10-40 mm from the antenna feed. The correlation of mean values of SWV with location (within, border, or outside necrotic area) at gross pathology was evaluated. RESULTS: In controlled hyperthermia experiments, a steep transition in liver stiffness was observed at 63.0 ± 2.4 °C (SWV 3.54 ± 0.68 m/s). Avg60 was of 2.5 m/s. In 8/9 MWA experiments, interrupted when SWV of 3 m/s was measured, the ROI was at the inner side of the necrotic area border at pathology (accuracy 89%). No correlation between SWV values for outside, border, and within necrosis could be identified. CONCLUSIONS: pSWE can provide a velocity threshold predictive of the presence of coagulation necrosis during MWA in ex vivo liver model. However, pSWE is not able to reliably capture changes in stiffness within, at the border, and outside the necrotic zone in this experimental model.

Tissue shrinkage in microwave ablation of liver: an ex vivo predictive model.

PURPOSE: The aim of this study was to develop a predictive model of the shrinkage of liver tissues in microwave ablation. METHODS: Thirty-seven cuboid specimens of ex vivo bovine liver of size ranging from 2 cm to 8 cm were heated exploiting different techniques: 1) using a microwave oven (2.45 GHz) operated at 420 W, 500 W and 700 W for 8 to 20 min, achieving complete carbonisation of the specimens, 2) using a radiofrequency ablation apparatus (450 kHz) operated at 70 W for a time ranging from 6 to 7.5 min obtaining white coagulation of the specimens, and 3) using a microwave (2.45 GHz) ablation apparatus operated at 60 W for 10 min. Measurements of specimen dimensions, carbonised and coagulated regions were performed using a ruler with an accuracy of 1 mm. Based on the results of the first two experiments a predictive model for the contraction of liver tissue from microwave ablation was constructed and compared to the result of the third experiment. RESULTS: For carbonised tissue, a linear contraction of 31 ± 6% was obtained independently of the heating source, power and operation time. Radiofrequency experiments determined that the average percentage linear contraction of white coagulated tissue was 12 ± 5%. The average accuracy of our model was determined to be 3 mm (5%). CONCLUSIONS: The proposed model allows the prediction of the shrinkage of liver tissues upon microwave ablation given the extension of the carbonised and coagulated zones. This may be useful in helping to predict whether sufficient tissue volume is ablated in clinical practice.

Microwave ablation of primary and secondary liver tumours: ex vivo, in vivo, and clinical characterisation.

PURPOSE: The aim of this study was to compare the performance of a microwave ablation (MWA) apparatus in preclinical and clinical settings. MATERIALS AND METHOD: The same commercial 2.45 GHz MWA apparatus was used throughout this study. In total 108 ablations at powers ranging from 20 to 130 W and lasting from 3 to 30 min were obtained on ex vivo bovine liver; 28 ablations at 60 W, 80 W and 100 W lasting 5 and 10 min were then obtained in an in vivo swine model. Finally, 32 hepatocellular carcinomas (HCCs) and 19 liver metastases in 46 patients were treated percutaneously by administering 60 W for either 5 or 10 min. The treatment outcome was characterised in terms of maximum longitudinal and transversal axis of the induced ablation zone. RESULTS: Ex vivo ablation volumes increased linearly with deposited energy (r2 = 0.97), with higher sphericity obtained at lower power for longer ablation times. Larger ablations were obtained on liver metastases compared to HCCs treated with 60 W for 10 min (p < 0.003), as ablation diameters were 4.1 ± 0.6 cm for metastases and 3.7 ± 0.3 cm for HCC, with an average sphericity index of 0.70 ± 0.04. The results on the in vivo swine model at 60 W were substantially smaller than the ex vivo and clinical results (either populations). No statistically significant difference was observed between ex vivo results at 60 W and HCC results (p > 0.08). CONCLUSIONS: For the selected MW ablation device, ex vivo data on bovine liver was more predictive of the actual clinical performance on liver malignancies than an in vivo porcine model. Equivalent MW treatments yielded a significantly different response for HCC and metastases at higher deposited energy, suggesting that outcomes are not only device-specific but must also be characterised on a tissue-by-tissue basis.

Microwave ablation of hepatocellular carcinoma.

Although surgical resection is still the optimal treatment option for early-stage hepatocellular carcinoma (HCC) in patients with well compensated cirrhosis, thermal ablation techniques provide a valid non-surgical treatment alternative, thanks to their minimal invasiveness, excellent tolerability and safety profile, proven efficacy in local disease control, virtually unlimited repeatability and cost-effectiveness. Different energy sources are currently employed in clinics as physical agents for percutaneous or intra-surgical thermal ablation of HCC nodules. Among them, radiofrequency (RF) currents are the most used, while microwave ablations (MWA) are becoming increasingly popular. Starting from the 90s', RF ablation (RFA) rapidly became the standard of care in ablation, especially in the treatment of small HCC nodules; however, RFA exhibits substantial performance limitations in the treatment of large lesions and/or tumors located near major heat sinks. MWA, first introduced in the Far Eastern clinical practice in the 80s', showing promising results but also severe limitations in the controllability of the emitted field and in the high amount of power employed for the ablation of large tumors, resulting in a poor coagulative performance and a relatively high complication rate, nowadays shows better results both in terms of treatment controllability and of overall coagulative performance, thanks to the improvement of technology. In this review we provide an extensive and detailed overview of the key physical and technical aspects of MWA and of the currently available systems, and we want to discuss the most relevant published data on MWA treatments of HCC nodules in regard to clinical results and to the type and rate of complications, both in absolute terms and in comparison with RFA.

Influence of the target tissue size on the shape of ex vivo microwave ablation zones.

PURPOSE: The aim of this study was to numerically and experimentally characterise the influence of tissues dimensions on the size and shape of microwave-induced ablation zones. MATERIALS AND METHODS: A 2.45 GHz interstitial antenna was introduced into ex vivo bovine liver samples, delivering 60 W for 10 min; then the dimensions of the coagulated area were measured. Ablations were performed both in large samples (termed unrestricted tissue) for characterising the tissue response, and in thin samples, whose dimensions in the plane perpendicular to the antenna were smaller than the short axis of the ablated area obtained in unrestricted samples. In the numerical study the electromagnetic field emitted from the antenna and the corresponding temperature increase were evaluated in both unrestricted and thin tissue samples. RESULTS: When the height of the tissue was smaller than the ablation diameter measured in unrestricted samples, a 7.5% increase in length of the ablated zone was experimentally observed. When both the height and width were lower than the diameter measured in unrestricted samples, an elongation of about 23.4% was experimentally obtained. The numerical study showed that the boundary conditions between the target tissue and the surrounding materials are critical. CONCLUSIONS: The ex vivo performances of microwave ablation devices are notably influenced by the shape and dimension of the tissues where the procedure takes place. Accordingly, dedicated interventional protocols should be developed for treatment planning on targets of different shape and size.

Characterisation of tissue shrinkage during microwave thermal ablation.

PURPOSE: The aim of this study was to characterise changes in tissue volume during image-guided microwave ablation in order to arrive at a more precise determination of the true ablation zone. MATERIALS AND METHODS: The effect of power (20-80 W) and time (1-10 min) on microwave-induced tissue contraction was experimentally evaluated in various-sized cubes of ex vivo liver (10-40 mm ± 2 mm) and muscle (20 and 40 mm ± 2 mm) embedded in agar phantoms (N = 119). Post-ablation linear and volumetric dimensions of the tissue cubes were measured and compared with pre-ablation dimensions. Subsequently, the process of tissue contraction was investigated dynamically during the ablation procedure through real-time X-ray CT scanning. RESULTS: Overall, substantial shrinkage of 52-74% of initial tissue volume was noted. The shrinkage was non-uniform over time and space, with observed asymmetry favouring the radial (23-43 % range) over the longitudinal (21-29%) direction. Algorithmic relationships for the shrinkage as a function of time were demonstrated. Furthermore, the smallest cubes showed more substantial and faster contraction (28-40% after 1 min), with more considerable volumetric shrinkage (>10%) in muscle than in liver tissue. Additionally, CT imaging demonstrated initial expansion of the tissue volume, lasting in some cases up to 3 min during the microwave ablation procedure, prior to the contraction phenomenon. CONCLUSIONS: In addition to an asymmetric substantial shrinkage of the ablated tissue volume, an initial expansion phenomenon occurs during MW ablation. Thus, complex modifications of the tissue close to a radiating antenna will likely need to be taken into account for future methods of real-time ablation monitoring.

A minimally invasive antenna for microwave ablation therapies: design, performances, and experimental assessment.

A new coaxial antenna for microwave ablation therapies is proposed. The antenna design includes a miniaturized choke and an arrowhead cap to facilitate antenna insertion into the tissues. Antenna matching and the shape and dimension of the area of ablated tissue (thermal lesion) obtained in ex vivo conditions are evaluated both numerically and experimentally, finding an optimal agreement between numerical and experimental data. Results show that the antenna is well matched, and that it is able to produce a thermal lesion with an average length of 6.5 cm and an average diameter of 4.5 cm in ex vivo bovine liver when irradiates 60 W for 10 min. Finally, the dependence of antenna performances on possible changes in the antenna's structure is investigated, finding an optimal stability with respect to manufacturing tolerances and highlighting the fundamental role played by the antenna's choke.

In vivo microwave-induced porcine kidney thermoablation: results and perspectives from a pilot study of a new probe.

OBJECTIVE: To test the in vivo effects (toxicity, completeness of necrosis, dimensions of the lesion) of microwave thermoablation on porcine kidneys, using the Amica Probe v3 (Hospital Service SpA, Aprilia, Italy), in a refrigerated 17-G microwave applicator, that can be used to induce a spherical necrotic area. PATIENTS AND METHODS: Six pigs were used; each kidney was treated, with no kidney pedicle clamping, by microwave thermoablation at least in three different zones with different exposure times and power, during open surgery. Twelve kidneys had 32 microwave thermoablations overall. The kidneys were then surgically removed, and necrotic lesions measured and evaluated microscopically. The sphericity index (SI) was also calculated to evaluate lesion reproducibility. Areas of renal tissue that were missed were then microscopically evaluated by NADH in vivo staining. RESULTS: In all, 32 thermoablations were applied; the mean (sd) lesion diameter ranged from 1.2 (0.3) to 4.2 (0.1) cm and changed in relation to both power and time of exposure. The 50-W power particularly induced necrotic renal lesions ranging from 1.9 (0.2) to 4.2 (0.1) cm as a function of the time of exposure and the optimal SI (1.04). Pathological evaluation showed no skipped areas in the context of the lesion, or healthy kidney tissue damage close to necrotic lesions. CONCLUSIONS: Thermoablation with the Amica probe is safe and showed excellent in vivo effects in this porcine model. Increasing the exposure time at 50 W power could be a useful percutaneous minimally invasive treatment for small solid masses (<4.2 cm), avoiding the risk of missing tumour areas or kidney parenchymal damage from microwave treatment.

Transperineal microwave thermoablation in patients with obstructive benign prostatic hyperplasia: a phase I clinical study with a new mini-choked microwave applicator.

PURPOSE: To evaluate the tolerability and safety of a newly designed probe for trans-perineal microwave thermoablation (TPMT) of the prostate in patients with benign prostatic hyperplasia (BPH), and the in vivo microwave effects on prostatic tissue. PATIENTS AND METHODS: Nine patients with obstructive BPH who were candidates for open prostatectomy were selected for this study. Under local anesthesia and transrectal ultrasound monitoring, all patients underwent a single standardized application of TPMT. The visual analog scale (VAS) and Short Form-36 health survey (SF-36) questionnaire were administered to each patient prior to, during, and 1 month after TPMT in order to evaluate pain and quality of life. Then the International Index of Erectile Function (IIEF-5) and International Prostate Symptom Score (IPSS) questionnaires were administered to each patient at baseline and 1 month after prostatectomy in order to evaluate sexual and urinary function, respectively. Then all patients were divided into three groups and underwent open prostatectomy 7, 15, and 30 days after TPMT, respectively. The prostatic adenomas were then evaluated by a pathologist. RESULTS: No adverse events from TPMT treatment were noted. In particular, no patients reported local, pelvic, or abdominal pain during the procedure or subsequent alterations of defecation rhythm, ano-rectal/intestinal problems, or hematuria. No differences in quality of life or in sexual function were reported. The diameters of the lesions obtained with TPMT treatment ranged from 16 to 18.1 mm in all patients. Quasi-spheroid lesions with a well-defined area of complete coagulative necrosis were documented in all removed adenomas 7, 15, and 30 days after TMPT. CONCLUSIONS: The AMICA-PROBE is a safe, well-tolerated, and repeatable method to treat BPH with microwave thermotherapy. The spheroid lesions obtained demonstrated the maximal control over the radial and longitudinal coagulative effects of the therapy. Phase II studies are needed to further evaluate the efficacy of this new probe.

A coaxial antenna with miniaturized choke for minimally invasive interstitial heating.

We present a new coaxial antenna for microwave interstitial coagulative therapy, working at 2450 MHz and endowed with a miniaturized sleeve choke in order to reduce back heating effects and make the system response less dependent on the antenna insertion depth into the tissue; the way the choke is implemented makes the overall transversal size minimum and allows small adjustments of the choke section length even during operation. We describe the main technical features of the antenna and show experimental results clearly proving the choke effectiveness. Numerical simulations well agree with experimental data, confirming the suitability of the proposed device for minimally invasive medical applications.