Evaluation of the effectiveness of radiofrequency ablation of colorectal cancer metastases using shear wave elastometry

Background. Radiofrequency ablation of metastatic foci in the liver is one of the therapeutic techniques indicated for patients with synchronous and/or metachronous colorectal cancer (CRC) metastases in the liver. Purpose – to investigate the feasibility of using ultrasound liver elastometry to monitor the implementation and evaluate the effectiveness of RFA of liver metastases of CRC. Materials and methods. A comparative study of the results of percutaneous RFA of hepatic metastases of CRC in two representative groups of patients aged 43 to 84 years (mean – 59.8 ± 10.0 years) was performed. Group I (main) included 20 patients who underwent RFA under the control of conventional gray-scale ultrasound (US) and ultrasound elastometry. Group II (comparison) included 18 patients who underwent RFA without ultrasound elastometry of the liver parenchyma. The technical effectiveness of RFA in both groups was assessed by the following general criteria: overlapping of the ultrasound image of the lesion with a hyperechoic «cloud» during ablation, overlapping of the metastasis zone with an area that does not accumulate contrast agent during computed tomography (CT) on the 1st–2nd day after RFA, overlapping of the metastasis zone with a reduced fluid content during magnetic resonance imaging (MRI) on the 1st–2nd day after RFA. The determination of the stiffness modulus of the ablation margin was used to monitor the procedure of percutaneous RFA of metastases in group I patients. To improve the long-term results of treatment, screening diagnostic measures were performed at 1, 3, 6, 12 and 24 months, including ultrasound, CT and MRI with intravenous contrast enhancement. Statistical data processing was performed using SPSS 21 software. Results. In group I, 31 foci ranging in size from 4 to 52 mm (mean – 19.0 ± 11.0 mm) underwent RFA. The initial values of the ablation edge stiffness modulus ranged from 4.6 to 9.2, averaging 6.12–1.12 kPa. The value of Youngʼs modulus of stiffness (YS) of the ablation margin, having reached its maximum values at the end of the operation, gradually decreased 1 and 3 days after it, while the surrounding parenchyma showed an increase in stiffness (p < 0.05) due to reactive tissue edema. An increase in the number of 12-minute RFA sessions, RFA time by 2.2 times (p = 0.033) and intervention by 1.8 times (p = 0.042) was found in group I. The primary efficacy of the intervention was 90% of cases in group I versus 74.1% in group II (OR 5.73; 95% CI [1.04–32.67]). Accordingly, the frequency of the need for repeated ablation was significantly lower among patients in group I – 2 (5.9%) versus 7 (25.7%) in group II (p = 0.036). No significant differences between groups were found in adverse reactions and complications of RFA. Conclusions. The stiffness modulus of hepatic CRC metastases and surrounding unchanged parenchyma according to shear wave ultrasound elastography is a criterion for the primary efficacy of RFA. The criterion for achieving the target value of the ablation margin is the excess of the initial (before ablation) stiffness modulus of the adjacent metastatic focus. An additional criterion for the effectiveness of the performed RFA is the dynamics of the ablation margin MU values during the first 3 days after the intervention.