Predicting RadIotherapy ReSponse of Rectal Cancer With MRI and PET

Patients will have an early MRI and PET/CT - 2 weeks after commencing chemo/RT. A limited range PET/CT will look at parameters: SUVmaxm PERCIST, RECIST 1.1, ΔSUV (PET1-2), ΔSUV (early -late), Glycolytic tumour volume (GTV). MRI T2 (1-3mm slice as per NS Radiology protocol and ESGAR guideline) will look at parameters: DWI \& ADC value (preferably on a single camera with reproducible ADC value), Local Staging, MRF involvement, EMVI, nodal status, MR volumetry, and desmoplastic reaction.

Patients will have late a MRI and PET/CT 6 weeks post chemo/RT. A whole body PET/CT will look at parameters: SUVmaxm PERCIST, RECIST 1.1, ΔSUV (PET1-2), ΔSUV (early -late), Glycolytic tumour volume (GTV). MRI T2 (1-3mm slice as per NS Radiology protocol and ESGAR guideline) will look at parameters: DWI \& ADC value (preferably on a single camera with reproducible ADC value), Local Staging, MRF involvement, EMVI, nodal status, MR volumetry, and desmoplastic reaction.