Feasibility of diffusion-weighted magnetic resonance imaging in evaluation of early therapeutic response after CT-guided microwave ablation of inoperable lung neoplasms

Abstract

Objective To determine the early treatment response after microwave ablation (MWA) of inoperable lung neoplasms using the apparent diffusion coefficient (ADC) value calculated 24 h after the ablation. Materials and methods This retrospective study included 47 patients with 68 lung lesions, who underwent percutaneous MWA from January 2008 to December 2017. Evaluation of the lesions was done using MRI including DWI sequence with ADC value calculation pre-ablation and 24 h post-ablation. DWI-MR was performed with b values (50, 400, 800 mm2/s). The post-ablation follow-up was performed using chest CT and/or MRI within 24 h following the procedure; after 3, 6, 9, and 12 months; and every 6 months onwards to determine the local tumor response. The post-ablation ADC value changes were compared to the end response of the lesions. Results Forty-seven patients (mean age: 63.8 ± 14.2 years, 25 women) with 68 lesions having a mean tumor size of 1.5 ± 0.9 cm (range: 0.7–5 cm) were evaluated. Sixty-one lesions (89.7%) showed a complete treatment response, and the remaining 7 lesions (10.3%) showed a local progression (residual activity). There was a statistically significant difference regarding the ADC value measured 24 h after the ablation between the responding (1.7 ± 0.3 × 10−3 mm2/s) and non-responding groups (1.4 ± 0.3 × 10−3 mm2/s) with significantly higher values in the responding group (p = 0.001). A suggested ADC cut-off value of 1.42 could be used as a reference point for the post-ablation response prediction (sensitivity: 66.67%, specificity: 84.21%, PPV: 66.7%, and NPV: 84.2%). No significant difference was reported regarding the ADC value performed before the ablation as a factor for the prognosis of treatment response (p = 0.86). Conclusion ADC value assessment following ablation may allow the early prediction of treatment efficacy after MWA of inoperable lung neoplasms. Key Points • ADC value calculated 24 h post-treatment may allow the early prediction of MWA efficacy as a treatment of pulmonary tumors and can be used in the early immediate post-ablation imaging follow-up. • The pre-treatment ADC value of lung neoplasms is not different between the responding and non-responding tumors.

Editorial: Local ablative therapies for the management of lung cancer

“…MR-guided MWA for lung malignant tumor could also be another option, just previously explored in rabbits ( 20 , 21 ). Lin et al.…”

“…A topic that could be interesting in the treatment of lung tumors with MWA is also represented by the ability to predict and evaluate the treatment efficacy. In detail, apparent diffusion coefficient (ADC) of MRI calculated 24 hours after MWA of lung cancer could be effectively used to predict the early treatment efficacy ( 20 ).…”

Magnetic Resonance Imaging for Guidance and Follow-up of Thoracic Needle Biopsies and Thermal Ablations

“…42,45,49 On DWI, viable tissue presents as focal signal in the ablation zone, while necrotic tissue presents as a lack of signal. Two groups have shown that changes in ADC from 2 days pre-MWA/ 4 days pre-RFA to 24 hours post-MWA/ 3 days post-RFA can predict the treatment response in lung tumors before a change in tumor size becomes detectable on CT. 44,46 Postablation ADC was significantly lower in incompletely treated tumors compared with completely treated tumors and a small decrease in ADC value several days after heat-based ablation may suggest that local progression is likely on follow-up CT. There was no statistically significant correlation regarding the ADC value performed before the ablation between the responding and nonresponding tumors.…”

“…[42][43][44] Data following MWA in the lung are limited to a comparison of findings on CE MRI and NCE CT of 77 tumors in 49 patients as well as DWI of 68 tumors in 47 patients, both at 24-hour post-ablation. 45,46 After lung cryoablation, 35 lung tumors in 30 patients were followed up for a median of 22 months (range, 3 to 62 mo) using a CE 3.0 T MRI and a scanner with unspecified field strength (Table 3). 48,49…”

“…There was no statistically significant correlation regarding the ADC value performed before the ablation between the responding and nonresponding tumors. Vogl and colleagues 46 suggested a cutoff ADC value of 1.42 as a reference point for the prediction of tumor response following MWA, reporting a sensitivity of 66.67%, specificity of 84.21%, positive predictive value of 66.7%, and negative predictive value of 84.2%.…”