In this chapter, we describe the role of imaging in restaging rectal cancer after preoperative neoadjuvant chemoradiation therapy (CRT); especially we focused on its potential role in the prediction of complete tumor regression (pCR). On standard MRI, a normalized rectal wall without any detectable wall thickening is considered a definite criterion for a pCR. On diffusion-weighted MR imaging (DWI), strength of evidence scored as moderate (2/5) the value of pretherapy apparent diffusion coefficient (ADC) as possible indicator of outcome of therapy and as moderate-firm percentage increase of ADC value measurement during treatment for personalized treatment management. On posttreatment presurgical evaluation, the challenge will remain the detection of microscopically small clusters of residual tumor cells, which are difficult to detect—even at histology—and are currently beyond the detection level of any available imaging modality.
FDG PET-CT shows great promise as a tool to evaluate the effectiveness of rectal cancer neoadjuvant therapy as it has demonstrated high predictive value in several studies. However, it is important to note that also PET cannot be considered as surrogate for pCR because patients with complete PET response after neoadjuvant CRT often show residual microscopic disease. However, promising data derive from metabolic response assessment during neoadjuvant CRT allowing for tailored therapy using alternative dosing, fractionation, or agents.
We describe in the text and analyze in the figures the advantages and disadvantages of these techniques in rectal cancer response evaluation and whether they can be complementary.
Rectal Cancer Apparent Diffusion Coefficient Standardize Uptake Value Advanced Rectal Cancer Total Lesion Glycolysis
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