Rectal perfusion parameters normalised to tumour-free rectal wall can predict response to neoadjuvant...

To evaluate absolute changes in quantitative and semi-quantitative perfusion parameters using a newer approach of comparing these parameters with tumour-free normal rectal wall (i.e., relative/normalised change) in predicting complete pathological response to chemoradiotherapy.

Perfusion parameters measured before and after treatment of 10 patients with histopathologically proven rectal cancer that showed complete treatment response (Group 1) were compared with 10 patients with residual tumour on histopathology following treatment (Group 2). Quantitative perfusion MRI parameters (Ktrans: volume transfer coefficient reflecting vascular permeability, Kep: flux rate constant, Ve: extracellular volume ratio reflecting vascular permeability, integral of area under the curve (IAUC); Toft model) were quantified by manually delineating a region of interest in the upper, mid and lower third of the tumour (1 cm²), in addition similar parameters were obtained from the normal rectal wall at least 1 cm away from the potential resection margin, absolute as well as relative perfusion values normalised to that of the normal rectal wall were evaluated. The differences in absolute and normalised qualitative parameters were compared within each group using paired t-tests and between each group using analysis of variance (ANOVA).

Wash-in, wash-out, positive enhancement integral (PEI), Ktrans, IAUC in the complete pathological responders when compared to the adjacent normal rectal wall showed ratios approaching 1, suggesting that rectal perfusion is similar to the adjacent normal rectal wall in complete pathological responders. The difference in the normalised values in the responders and non-responders was statistically significant.

Perfusion parameters can be used in predicting response to treatment, when normalised to the adjacent normal rectal wall.