Aim
To evaluate the change in signal intensity (SI) and volume (V) from multiparametric magnetic resonance imaging (MRI) for assessing the response of locally advanced rectal cancer (LARC) to chemoradiotherapy (CRT).
Materials and methods
Eight‐two LARC patients who underwent pre‐ and post‐CRT T2‐weighted (T2W), apparent diffusion coefficient (ADC), and contrast‐enhanced T1‐weighted (ceT1W) MRI were retrospectively analyzed. The change of volume (%△V) and relative SI ratio (%△SIR) from each sequence were determined. All LARCs were confirmed pathologically and classified as tumor regression grade (TRG) ‐0, 1, 2,or 3. Descriptive statistics and receiver operating characteristic (ROC) analysis, with calculation of area under the curve (AUC), were used to compare the diagnostic performances.
Results
Sixteen patients had TRG‐0, 15 had TRG‐1, 35 had TRG‐2, and 16 had TRG‐3. Except for ADC‐%△SIR, the remaining %△V and %△SIR values on MR sequences had significant differences among the four groups. The %△V and %△SIR (alone or together) did not distinguish TRG‐1 from TRG‐2, nor TRG‐2 from TRG‐3; however, differences between other TRGs were identified by %△V and %△SIR. The combined use of ADC‐%△V and T2W‐%△SIR provided the best diagnostic performance in distinguishing of TRG‐0 from TRG‐2 (AUC: 0.954) and from TRG‐3 (AUC: 1.000).
Conclusions
Preoperative MRI of LARC patients after CRT has high diagnostic value for determination TRG, and may therefore improve the selection of patients most suitable for surgery.