The Role of Shear Wave Elastography in Monitoring Rectal Cancer Treatment

Reem Mislati

Supervised by Marvin M. Doyley

703 Computer Studies Building

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Rectal cancer is a devastating malignancy, ranking as the second leading cause of cancer-related deaths. The standard care for locally advanced rectal cancer includes neoadjuvant treatments such as short-course radiation therapy or chemoradiotherapy, followed by total mesorectal surgery. Clinical studies have shown that some patients achieve a complete clinical response (cCR) post-neoadjuvant treatment, thus avoiding the complications associated with surgery. Consequently, extensive research has been directed toward understanding the variability in response to neoadjuvant treatments by examining changes in the tumor microenvironment (TME).

These changes in the TME are mirrored in the tumor’s mechanical properties. Shear wave elastography, a non-invasive imaging modality, measures these mechanical properties of tissue. Parameters such as shear wave speed and shear wave attenuation coefficient indirectly measure tissue stiffness and viscosity. Monitoring changes in these parameters could reflect effective alterations in the TME due to treatment.

This thesis aims to establish shear wave elastography as a method for monitoring rectal cancer treatment. To achieve this, we set the following objectives: (1) develop a technique to quantify the viscoelastic behavior of biological tissues, specifically focusing on the shear wave attenuation coefficient; (2) determine if shear wave speed and attenuation coefficient can differentiate between radiation-responsive and non-responsive tumors; (3) investigate the potential of shear wave elastography in assessing the immune system’s response to treatment.

Our studies demonstrated that shear wave elastography effectively stratifies non-responsive and responsive rectal tumors treated with short-course radiation therapy. We found that non-responsive tumors are generally stiffer and less viscous than responsive tumors. Additionally, a negative correlation was observed between shear wave speed and the level of tumor-infiltrating immune cells, where high levels of tumor-infiltrating-immune cells correlate with improved survival and treatment outcomes.