ShearWave Elastography - A New Quantitative Assessment of Post-Irradiation Neck Fibrosis

Purpose: Shear wave elastography (SWE) is a new technique which provides quantitative assessment of soft tissue stiffness. The aim of this study was to assess the reliability of SWE stiffness measurements and its usefulness in evaluating post-irradiation neck fibrosis. Materials and Methods: 50 subjects (25 patients with previous radiotherapy to the neck and 25 sex and age-matched controls) were recruited for comparison of SWE stiffness measurements (Aix-plorer, Supersonic Imagine). 30 subjects (16 healthy individuals and 14 post-irradiated patients) were recruited for a reliability study of SWE stiffness measurements. SWE stiffness measurements of the sternocleidomastoid muscle and the overlying subcutaneous tissues of the neck were made. The cross-sectional area and thickness of the sternocleidomastoid muscle and the overlying subcutaneous tissue thickness of the neck were also measured. The post-irradiation duration of the patients was recorded. Results: The intraclass correlation coefficients for the intraoperator and interoperator reliability of deep and subcutaneous tissue SWE stiffness ranged from 0.90 - 0.99 and 0.77 - 0.94, respectively. The SWE stiffness measurements (mean +/- SD) of deep and subcutaneous tissues were significantly higher in the post-irradiated patients (64.6 +/- 46.8 kPa and 63.9 +/- 53.1kPa, respectively) than the sex and age-matched controls (19.9 +/- 7.8 kPa and 15.3 +/- 8.37 respectively) (p < 0.001). The SWE stiffness increased with increasing post-irradiation therapy duration in the Kruskal Wallis test (p < 0.001) and correlated with muscle atrophy and subcutaneous tissue thinning (p < 0.01). Conclusion: SWE is a reliable technique and may potentially be an objective and specific tool in quantifying deep and subcutaneous tissue stiffness, which in turn reflects the severity of neck fibrosis.