This guideline is one of a set developed by the Program in Evidence-Based Care's (PEBC) Diagnostic Imaging Guidelines Panel, using methods adapted from the Practice Guidelines Development Cycle. These guidelines are intended to:
- Promote evidence-based practice
- Provide guidance to clinicians about which imaging techniques are the most appropriate to use in the management of their patients
- Provide information that is useful to those charged with planning for the number of imaging machines needed for patients with cancer in Ontario
Panel members included medical, radiation, and surgical oncologists, diagnostic radiologists, and methodologists. Prior to embarking on guideline development, the members disclosed information on potential conflict of interest. On reviewing that information, the panel found no areas of concern among the information provided by the panel members on the PEBC's standard conflict-of-interest form. Three panel members were investigators in trials of positron emission tomography (PET), but the panel decided that this was not in conflict with developing a guideline on computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound. The lead author of this guideline report on imaging in colorectal cancer declared no conflicts of interest. The PEBC is editorially independent of Cancer Care Ontario and the Ontario Ministry of Health and Long-term Care.
The Diagnostic Imaging Guideline Panel:
- Formulated a set of guideline questions relevant to cancer care in Ontario
- Systematically reviewed existing evidence-based guidelines and evidence from primary studies
The Colorectal Working Panel:
- Considered the quantity, quality, consistency, completeness, and relevance of the available evidence
- Drafted recommendations
- Consulted members of relevant PEBC Disease Site Groups for feedback
Evidence and expert opinion was considered in terms of whether imaging should be conducted (e.g., How often would diagnostic imaging with CT, MRI, or ultrasound revise staging in patients with cancer?) and then in terms of which imaging test would be most appropriate (e.g., Should ultrasound, CT, or MRI be used to detect liver metastases?). An informal consensus process was used to reach agreement on recommendations.
A focused external review process was planned for each document, utilizing the expertise of a small panel of experts. This review was obtained through a mailed survey consisting of items that addressed the quality of the draft report and recommendations and whether the recommendations should serve as a practice guideline.
Discussion and Consensus
CT and MRI are superior to ultrasound to detect liver metastases. For rectal cancer, and with regard to predicting tumour penetration through the rectal wall or positive nodes, transrectal ultrasound is slightly superior to CT or MRI, and equivalent to MRI with endorectal coil. This latter test is not widely available in Ontario. Of interest, it is likely that advances in technology will demonstrate similar staging accuracy for routine MRI versus MRI with endorectal coil. For example, it is the practice of one of the guideline authors to recommend MRI with surface coil to assess T and N categorization for patients with rectal cancer. Moreover, it should be recognized that the results of any imaging test are influenced by the expertise of the involved clinicians (i.e., tests are operator dependent). This is likely truer for ultrasound than for CT or MRI. Thus, if transrectal ultrasound or cross sectional imaging determinations of T or N category will be used to make neoadjuvant therapy recommendations for patients with rectal cancer, individual centres may wish to compare the accuracy of such efforts using postoperative pathology staging. A positive test for regional lymph node involvement with tumour will be incorrect approximately 30% of the time with transrectal ultrasound, CT or MRI, and 20% of the time with MRI with endorectal coil. Potential involvement of the mesorectal margin by tumour can be assessed by CT or MRI.
There was no evidence to determine which imaging modality would be more useful in determining tumour response to therapy—therapy given preoperatively or for palliative purposes. There is evidence from a guideline produced by the Program in Evidence-based Care Gastrointestinal Disease Site Group (PEBC GI DSG) on the frequency of tests that should be performed on patients with varying stages of colorectal cancer presented in the guideline and recommendations. CT and MRI are equivalent in their ability to detect disease recurrence.