Therapeutic response assessment of high-intensity focused ultrasound (HIFU) ablation for pancreatic cancer: Utility of contrast-enhanced ultrasonography (CEUS)

Purpose: To investigate the utility of contrast-enhanced ultrasound (CEUS) in the assessment of the therapeutic response to high-intensity focused ultrasound (HIFU) ablation for pancreatic cancer.

Material and methods: 28 patients (11 female, 17 male, mean age 66 years, range 47 – 82) with pancreatic cancer (mean 3.5 cm, range 2.2 – 6.6 cm; mean 17.7 cm³, range 3.2 – 60.6 cm³) were treated with ultrasound-guided HIFU. All patients underwent CEUS and contrast-enhanced MRI (CEMRI) before and after HIFU. Following HIFU, CEUS and CEMRI were performed after 6 weeks (n = 17) and 3 (n = 15), 6 (n = 7), 9 (n = 3) and 12 (n = 3) months. CEUS and CEMRI were compared by two investigators evaluating the presence or absence of residual unablated tumour, size and volume changes compared to pre- and post-HIFU-ablation. The lesions' contrast enhancement characteristics were graded using a four-point scale (0-none, 1-mild, 2-moderate, 3-intense).

Results: CEUS was impeded early after HIFU due to edema in the acoustic pathway in 6/28 patients. A lack of contrast enhancement in the treated regions in terms of successful ablation was achieved in all patients. A mild ringlike peripheral enhancement around the ablated volume was observed on both CEUS and CEMRI in 7/28 patients up to 6 weeks after HIFU, but vanished in the further follow-up. The sizes and volumes of all tumours decreased in different degrees during follow-up. A tumour recurrence seen as newly emerging nodular enhancement was detected by both methods in 2/28 patients. No significant differences were observed between CEUS and CEMRI when evaluating tumour sizes (P = 0.415), volumes (p = 0.181) and contrast enhancement characteristics (p = 0.146). Correlation analysis showed a good correlation regarding tumour sizes (r = 0.677,p < 0.001) and volumes (r = 0.936,p < 0.001) measured by CEUS and CEMRI.

Conclusions: CEUS is useful for early and follow-up evaluation of therapeutic effects after HIFU-ablation for pancreatic cancer, but may be hindered by edema in the acoustic pathway early after HIFU.

Fig. 1: CEMRI and CEUS after HIFU of pancreatic cancer