Rectal perfusion parameters normalized to tumour free rectal wall can predict complete pathological response to neoadjuvant chemoradiotherapy.

The aim of this study was to evaluate absolute and normalized change in qualitative and semi quantitative perfusion parameters in predicting complete pathological response to CRT. Perfusion parameters of Pre and post treatment imaging of histopathologically proven 10 patients with rectal cancer who had complete response and complete absence of tumour on histopathology following complete treatment ( Group 1) were compared with 10 patients with residual tumour on histopathology following treatment (Group 2). The two groups were matched for T stage of tumour. Semiquantittaive perfusion MRI parameters (Ktrans, Kep, Ve, IAUC; Toft model) were quantified by manually delineating a region of interest in the upper, mid and lower third of tumour at least 1cm square, in addition similar parameters were obtained from the normal rectal wall atleast 1cm away from the potential resection margin, absolute as well as values normalized values to the perfusion in the normal rectal wall were evaluated. Qualitative perfusion parameters were also assessed (wash in, wash out, TTP, AT, PEI, iAUC). After CRT, all patients underwent complete surgical resection and the surgical specimen served as the gold standard. Difference in absolute and normalized qualitative parameters were compared within each group using paired t-test and between each group using ANOVA. Washin, Washout, PEI, Ktrans, IAUC in the complete pathological responders when normalized to the adjacent normal rectal wall showed ratio’s approaching near 1 suggesting that rectal perfusion returns similar to the adjacent normal rectal wall in complete pathological responders. The difference in the normalized values in the responders and non responders was statistically significant. Within group change in absolute mean values in the responders and non responders was not statistically significant. Perfusion parameters can be used in predicting response to treatment, when normalised to the adjacent normal rectal wall.