Rectal cancer is one of the most frequent malignancies,
with incidence of 40 in 100,000.
The standard treatment for Locally Advanced Rectal Cancer (LARC,
≥T3; any T,
N+) is represented by neoadjuvant chemoradiation therapy (CRT),
followed by total mesorectal excision (TME) surgery.
CRT enables less invasive surgical treatment and has led to a reduction in local recurrence rates -from 25%-30% to less than 10%- with improved overall survival.
15-30% of patients achieve a pathological complete response (CR) after CRT.
For these patients,
some authors propose a ‘‘wait-and-see’’ policy,
reling on avoiding surgery and performing a careful and close follow-up.
An accurate assessment of tumor response after CRT is,
thus,
a very critical issue and becomes essential to indicate surgical strategy.
At the present,
it is performed using digital rectal examination,
endoscopy and biopsy,
although MRI has acquired an important role,
due to its quality of excellent soft tissue depiction,
its multi-planar and multi-parametric features.
Diffusion-Weighted Imaging (DWI) is a noninvasive technique,
which may be easily added to any standard MRI protocol.
The utility of combining functional information,
provided by DWI,
with morphologic information provided by high-resolution T2WI sequences,
has been already established,
improving the performance and confidence of radiologists in the assessment of tumor response.
Free diffusion of water molecules,
as happens in fibrosis,
characterized by a low cellular density,
results in a loss of signal,
whereas a restriction of water diffusion,
as observed in residual tumor areas,
due to high cellular density,
results in high signal on DWI.
Moreover,
DWI allows quantitative measure of apparent diffusion coefficient (ADC): it has been suggested that increased ADC values may be correlated with areas of reduced cell density,
whereas areas exhibiting low ADC values reflect dense cellular structures.
Therefore,
quantitative interpretation of the ADC may be used as a biomarker for treatment response.
Further evaluations in patients with LARC undergone to CRT and subsequent surgery are performed during pathological examination,
through reproducible parameters such as Tumor Regression Grade (TRG).
The objective of this study was to investigate the added value of both qualitative and quantitative evaluation of DWI in response assessment of LARC after CRT,
in order to distinguish good versus poor responders and identify pathologic CR.