In recent years the concept of organ sparing treatment in rectal cancer was introduced for selected good responders after neo-adjuvant treatment. In these patients replacement of the standard of care total mesorectal excision (TME) by transanal endoscopic microsurgery (TEM) or omission of surgery after chemoradiation (CRT) was proposed. Before organ sparing treatments could be applied in clinical practice a reliable patient selection procedure has to be available as only good treatment responders after neo-adjuvant therapy are candidates for such adapted therapy. Different imaging modalities have been studied for their ability to distinguish good treatment responders from others. Examples of such imaging modalities with some promising results regarding response assessment are fludeoxyglucosepositron emission tomography (FDG-PET), T2-weighted magnetic resonance imaging (T2w-MRI), dynamic contrast enhanced magnetic resonance imaging and diffusion weighted MR imaging (DW-MRI). Besides these modalities dynamic contrast enhanced ultrasound (D-CEUS) is a new modality used for tissue characterization and therapy response assessment in several tumor locations, like liver tumors and breast cancer. D-CEUS reflect tissue vascular perfusion. For rectal cancer, the value of D-CEUS for pathological response prediction and assessment has never been assessed. Therefore, in this study we assessed D-CEUS to predict and assess pathological response in rectal cancer after neo-adjuvant CRT.

Inclusion Criteria:

• Histologically confirmed rectal carcinoma
• Stade ≥T2 and tumor size ≥3cm
• No detectable metastases
• Patient ≥ 18 years
• Patient information and written informed consent form signed
• Patient who can receive radiotherapy and chemotherapy
• Negative pregnancy test in women of childbearing potential
• Patient covered by a Social Security system

Exclusion Criteria:

• Indication for immediate surgery
• Primary tumor not measured at the MRI before inclusion
• Previous pelvic radiotherapy
• Contraindication to SONOVUE or MRI