Can diffusion-weighted MRI determine complete responders after neoadjuvant chemoradiation for locally advanced rectal cancer?

Abstract

N eoadjuvant chemoradiotheraphy (CRT) improves tumor downstaging, pathological complete response (pCR), and local control (1, 2). pCR rates of 13%-30% have been reported in phase II and phase III trials following 5-fluorouracil-based preoperative CRT (3, 4). Currently, management of patients with clinical complete response (cCR) remains controversial (5-8).A recent meta-analysis including 218 phase I/II or retrospective studies and 28 phase III trials of adjuvant CRT reported that T3 rectal cancer is associated with high local recurrence rates after nonsurgical treatment (9). In addition, similiar results were recently shown from a study using a "wait-and-see" policy after CRT (10).Accurate imaging methods are needed to evaluate CRT responses, and post-CRT magnetic resonance imaging (MRI) is frequently used for this purpose. However, the method has low accuracy in predicting the pathological stage of the tumor and can often overstage T1 and T2 tumors due to the limited capability of MRI to differentiate viable tumor, residual fibrotic nontumoral tissue, and a desmoplastic reaction. Understaging of irradiated rectal cancer can affect treatment planning, including the surgical strategy, and thus affects the tumor recurrence rate and prognosis (11).Diffusion-weighted (DW)-MRI is a functional imaging technique that yields qualitative and quantitative information and provides unique insights regarding tumor cellularity, integrity of cell membranes, and microcirculation.

MRI in local staging of rectal cancer: an update

“…A tumor volume reduction of more than 75% was significantly associated with pathologic complete response and higher disease-free survival rate (55). Both residual tumor and fibrosis may appear as decreased signal intensity areas, and DWI may help to differentiate residual viable tumor from fibrosis (56,57).…”

“…There is a growing literature on use of 3.0 T MRI in the local staging of rectal carcinoma (56)(57)(58) accuracy for determining sphincter-saving resectability. Currently, pelvic phased-array coil MR imaging at 3.0 T using high-resolution imaging protocol is generally considered the most accurate tool in local staging of rectal cancer.…”

“…DWI MRI has also been used to predict pathologic response after chemoradiation. Engin et al (57) showed that increase in apparent diffusion coefficient can predict therapy response. In many centers, DWI is now being used in routine MRI protocol as an adjunctive to T2-weighted images.…”

Diffusion‐weighted imaging: Apparent diffusion coefficient histogram analysis for detecting pathologic complete response to chemoradiotherapy in locally advanced rectal cancer

“…26,27 Although prior studies in rectal cancer showed only a significant increase in mean ADC values after CRT in rectal cancer, there are a few reports that assessed the change of skewness and kurtosis after CRT in rectal cancer. 28,29 The changes in the ADC histogram graph represent the influence of the treatment on the diffusion of water molecules through a decrease in the cellularity and integrity of cell membranes. We found that the change in ADC after CRT was also helpful for evaluating pCR, as well as post-CRT ADC values.…”

Multi-modality Therapy for Rectal Cancer—Past, Present, and Future

“…A prospective study from 2007 to 2010 showed that DW-MRI can accurately predict pCRs, although not unequivocally in all circumstances. 71 Retrospective studies have also suggested the utility of DW-MRI in assessing pCR. [72][73][74][75] The CARTS study is attempting to define a role for nonradical surgery and incorporates transanal endoscopic microsurgery (TEM) in well-defined patient subsets.…”