Fig. 12
Methods of DWI response evaluation. T2-weighted MRI (a, e), b1000 DWI (b, f), ADC map (c, g), and histograms of ADC values (d, h) of a patient with a mid-rectal tumor pre- (upper row) and post-CRT (bottom row). The images illustrate different ways DWI can be used to quantitatively assess response: pre-CRT the DWI tumor volume was 11.4 cm3 with a corresponding mean ADC of 1.12∙10−3 mm2/s. Post-CRT the DWI tumor volume decreased to 0.32 cm3, while the ADC value increased to 2.03∙10−3 mm2/s. The histograms show that the distribution of ADC values within the tumor shifted towards more high ADC values after CRT, indicating a good response. At histopathology, a small ypT2 tumor remnant with predominant fibrosis (Mandard tumor regression grade of 2) was found