Short summary

Rectal cancer treatment is planned based on the preoperative staging. However the differentiation between benign adenomas and early malignant changes is a difficult task. In our study we aim to investigate the diagnostic accuracy of shear wave elastography (SWE). SWE provides a value of tissue stiffness, which is expected to be a useful supplement to conventional endorectal ultrasonography.

Rationale

Rectal cancer is a frequent disease in Denmark with over 1500 new cases per year. Today, the 5-year survival of the disease is approx. 66%. The treatment is planned based on the preoperative staging of the tumour. Neither MRI nor transrectal ultrasound (TRUS) scanning, despite improvements, are optimal in differentiating malignant from benign rectal tumours. The same is true for lymph node diagnostics. Within the last year, two studies have been published showing that malignant tumours have a higher stiffness value by shear wave elastography (SWE) than benign rectal tumours.

Ultrasound-based elastography assessment is a relatively novel approach to rectal tumour evaluation but the method is already used in clinical practice for other organs. The principle of ultrasound elastography assessment of rectal tumours is to measure the change in tumour stiffness caused by malignant transformation.

There are two main elastography techniques. Until now, mainly strain elastography (quasi static elastography) has been investigated for the endoluminal staging of rectal tumours. Strain elastography enables visualization and semi-quantification of tissue elasticity by generating a color-coded map, which is superimposed onto a B-mode image. The subsequent elastography assessment can be performed by a semiquantitative strain ratio measurement or by subjective assessment of the elastogram using a continuous visual analog score (VAS) and/or a categorical W-score.

One study has shown that TRUS strain-elastography is able to differentiate adenomas from adenocarcinomas with a higher accuracy as compared to TRUS and magnetic resonance imaging (MRI). The method cannot be used to further improve the differentiation of T2-T4 stages, but a combined elastography and TRUS algorithm seems to improve the identification of tumours eligible for local resection compared to standard clinical evaluation with TRUS and MRI. TRUS elastography can potentially be used for the evaluation of perirectal lymph nodes, although no systematic studies have been published to the best of our knowledge.

The new SWE is an objective, possibly more reliable method of measuring stiffness compared to the semi-quantitative compression strain elastography. SWE produces shear waves in the target tissue using a short push pulse of less than 1 millisecond and a low mechanical index (MI) ≤ 1.9. These shear waves are detected by the system either by point SWE or two dimensional SWEs, and the velocity is measured in kPa or m/s (Figure 1). Slow shear waves correspond to soft tissue.

Another study on point SWE published promising results using the transperineal approach in showing that the tissue of rectal tumours responding to radiochemotherapy became softer. There is no data on tissue stiffness in relation to radiation dose. New knowledge in this area is obtainable by adding TRUS SWE to the upcoming Watchful Waiting protocol (WW3) on high vs. standard radiation dose.

Description of the cohort

Male and female adults, with a rectal lesion.

Data and biological material

Demografic data, age, gender Endoscopy, radiological and pathological findings. Surgical procedure.

Collaborating researchers and departments

Department of Radiology, Vejle hospital

• Professor Søren Rafael Rafaelsen, DMSc
• MS Malene Roland Vils Pedersen, PhD

Department of Surgery, Vejle Hospital

• MD Hans Rahr, DMSc

Department of Oncology, Vejle Hospital

• MD Lars Henrik Jensen, PhD