Intra-operative High-Intensity Focused Ultrasound in Patients With Colorectal Liver Metastases: A Prospective Ablate-and-Resect Study

High‑intensity focused ultrasound thermal ablation boosts the efficacy of immune checkpoint inhibitors in advanced cancers with liver metastases: A single‑center retrospective cohort study

High-intensity focused ultrasound thermal ablation (HIFU) is a novel non-invasive technique in the treatment of liver metastases (LIM) that allows focal destruction and is not affected by dose limits. This retrospective study aimed to explore the efficacy of HIFU in improving survival and the safety of the method in newly diagnosed patients with cancer with LIM who received first-line immune checkpoint inhibitor (ICI) therapy. Between January 2018 and December 2023, data from 438 newly diagnosed patients with cancer and LIM who were treated at Mianyang Central Hospital (Mianyang, China) were reviewed. A total of 94 patients were enrolled in this study, of whom 28 were diagnosed with lung carcinoma, 36 with gastric carcinoma, 11 with esophageal carcinoma, 7 with cholangiocarcinoma and 12 with other malignancies. The patients were divided into groups depending on whether they underwent HIFU. Progression-free survival (PFS), overall survival (OS) and adverse events (AEs) were compared. Clinicopathological features were analyzed using the chi-squared test. Of the 94 patients, 28 received ICI + HIFU as first-line treatment. After a median follow-up of 13.8 months, the median PFS and OS in the HIFU group were 2.38 times [10.95 vs. 4.60 months, 95% confidence interval (CI): 1.087-3.106, P<0.0001] and 1.84 times (19.6 vs. 10.67 months, 95% CI: 1.087-3.106, P=0.0418), respectively, higher than in the group without HIFU. All-cause AEs and immune-mediated AEs were similar between the groups with and without HIFU. However, the incidence of grade 1-2 immune-mediated AEs, troponin elevation, hepatotoxicity and renal dysfunction were more common in the current patients with LIM than those reported previously for the entire population. No immune-mediated AEs of grade ≥3 occurred in either group. HIFU prolonged the PFS and OS of first-line ICI in newly diagnosed patients with advanced cancer with LIM, with manageable safety and tolerability. The efficacy of HIFU in patients with LIM who plan to undergo ICI treatment warrants further prospective clinical investigation.

Intraoperative HIFU ablation of the liver at the hepatocaval confluence as adjunct to surgery: Preliminary animal experiments

Treating colorectal liver metastases (CLMs) located at the hepatocaval confluence with surgery is challenging due to its complexity and associated high risks of perioperative mortality and morbidity. Moreover, thermal ablation techniques are sensitive to the "heat-sink" effect, which reduces their efficacy when tumors are in contact with major blood vessels. In this study we evaluated the feasibility and safety of an intraoperative high-intensity focused ultrasound (HIFU) device for destroying liver tissue volumes sufficiently large to consider treating CLMs at the hepatocaval confluence. Experiments were conducted on six pigs that were followed up to 19 days after the treatment. One HIFU ablation in each animal was created using a 370 s exposure at 100 W. Homogeneous HIFU ablations of liver tissues were safely created at the hepatocaval confluence around the hepatic veins (HVs) in all animals. The targeted HVs were similar to those of humans, with an average diameter of 9.1 ± 1.4 mm. The longest and shortest axes of the HIFU ablations were on average 44.5 ± 11.5 mm and 26.7 ± 4.9 mm, respectively. These values indicate that this device could destroy CLMs up to 2 cm in diameter. Doppler acquisitions, MRI and histological analysis confirmed that HIFU ablations were in contact with the inferior vena cava and extended to the HV wall and that blood flow was maintained. This in vivo preclinical study showed that intraoperative HIFU destruction of liver tissues at the hepatocaval confluence under Doppler ultrasound guidance could therefore represent a new therapeutic option for CLMs.

2D ultrasound thermometry during thermal ablation with high-intensity focused ultrasound

The clinical use of high intensity focused ultrasound (HIFU) therapy for noninvasive tissue ablation has recently gained momentum. Guidance is provided by either magnetic resonance imaging (MRI) or conventional B-mode ultrasound imaging, each with its own advantages and disadvantages. The main limitation of ultrasound imaging is its inability to provide temperature measurements over the ranges corresponding to the target temperatures during ablative thermal therapies (between 55 °C and 70 °C). Here, variations in ultrasound backscattered energy (ΔBSE) were used to monitor temperature increases in liver tissue up to an absolute value of 90 °C during and after HIFU treatment. In vitro experimental measurements were performed in 47 bovine liver samples using a toroidal HIFU transducer operating at 2.5 MHz to increase the temperature of tissues. An ultrasound imaging probe working at 7.5 MHz was placed in the center of the HIFU transducer to monitor the backscattered signals. The free-field acoustic power was set to 9 W, 12 W or 16 W in the different experiments. HIFU sonications were performed for 240 s using a duty cycle of 83 % to allow ultrasound imaging and raw radiofrequency data acquisition during exposures. Measurements showed a linear relationship between ΔBSE (in dB) and temperature (r = 0.94, p < 0.001) over a temperature range from 37 °C to 90 °C, with a high reliability of temperature measurements below 75 °C. Monitoring can be performed at the frame rate of ultrasound imaging scanners with an accuracy within an acceptable threshold of 5 °C, given the temperatures targeted during thermal ablations. If the maximum temperature reached is below 70 °C, ΔBSE is also a reliable approach for estimating the temperature during cooling. Histological analysis shown the impact of the treatment on the spatial arrangement of cells that can explain the observed variation of ΔBSE. These results demonstrate the ability of ΔBSE measurements to estimate temperature in ultrasound images within an effective therapeutic range. This method can be implemented clinically and potentially applied to other thermal-based therapies.

In vivo exposure of the bladder using a non-invasive high intensity focused ultrasound toroidal transducer

A toroidal high-intensity focused ultrasound (HIFU) transducer was used to expose normal bladder wall tissues non-invasively in vivo in a porcine model in order to investigate the potential to treat bladder tumors. The transducer was divided into 32 concentric rings with equal surface areas, operating at 2.5 MHz. Eight animals were split into two groups of 4. In the first group, post-mortem evaluation was performed immediately after ultrasound exposure. In the second group, animals survived for up to seven days before post-mortem evaluation. The ultrasound imaging guided HIFU device was hand-held during the procedure using optical tracking to ensure correct targeting. One thermal lesion in each animal was created using a 40 s exposure at 80 acoustic Watts (free-field) in the trigone region of the bladder wall. The average (±Standard Deviation) abdominal wall and bladder wall thicknesses were 10.3 ± 1.4 mm and 1.1 ± 0.4 mm respectively. The longest and shortest axes of the HIFU ablations were 7.7 ± 2.9 mm and 6.0 ± 1.8 mm, respectively, resulting in an ablation of the whole thickness of the bladder wall in most cases. Ablation were performed at an average depth (distance from the skin surface to the centre of the HIFU lesion) of 42.5 ± 3.8 mm and extended throughout the thickness of the bladder. There were two cases of injury to tissues immediately adjacent to the bladder wall but without signs of perforation, as confirmed by histological analysis. Non-invasive HIFU ablation using a hand-held toroidal transducer was successfully performed to destroy regions of the bladder wall in vivo.

Quantitative ultrasound techniques for assessing thermal ablation: Measurement of the backscatter coefficient from ex vivo human liver

BACKGROUND

Understanding the changes occurring in biological tissue during thermal ablation is at the heart of many current challenges in both therapy and medical imaging research.

PURPOSE

The objective of this work is to quantitatively interpret the scattering response of human liver samples, before and after thermal ablation. We report acoustic measurements performed involving n = 21 human liver samples. Thermal ablation is achieved at temperatures between 45 and 80°C and quantification of the irreversible changes in acoustic attenuation and Backscattering Coefficient (BSC) is reported, with a particular attention to the latter.

METHODS

Both attenuation coefficient and BSCs were measured in the frequency range from 10 to 52 MHz. Scans were performed before heating and after cooling down. Attenuation coefficients were calculated using spectral difference method and BSC estimated using the reference phantom method.

RESULTS

Strong increases of attenuation coefficients and BSCs with heating temperature were observed. Quantitative ultrasonic parameters obtained with the polydisperse structure factor model (poly-SFM)are compared to histological observations and seen to be close to hepatocyte mean diameter (HMD).

CONCLUSIONS

The results presented in this study provide a description of the impact of thermal ablation in human liver tissue on acoustic attenuation and the BSC. For the first time, quantitative agreement between the Effective Scatterer Diameter (ESD) estimated from BSC and HMD was shown, highlighting the important role of cellular network in the scattering response of the medium. This core result is an important step toward the determination of the nature of scattering sources in biological tissues.