Functional MR imaging for response prediction in rectal cancer treatment

The standard of care treatment for locally advanced rectal cancer is neoadjuvant chemoradiation followed by total mesorectal excision. In recent years, organ-sparing treatments, instead of standard total mesorectal excision, are gradually introduced in the treatment of rectal cancer for patients with good response after neoadjuvant therapy. However, patient selection for organ-sparing treatments is still challenging as no optimal restaging modality is available after neoadjuvant chemoradiation. This thesis examined the value of functional MR imaging in the prediction of favourable pathological response after neoadjuvant therapy to determine its role in the selection of patients for organ-sparing treatments. First, the good potential of diffusion weighted imaging for pathological response assessment was shown, both during neoadjuvant therapy and after neoadjuvant therapy. Successively, the repeatability of apparent diffusion coefficient values from the diffusion weighted imaging was assessed to be able to distinguish therapy related response from measurement variations. Second, the good potential of dynamic contrast enhanced imaging for the selection of good pathological responders after neoadjuvant therapy was shown. Finally, the additional value of combining both functional imaging techniques and tumour volumetry was assessed which showed the highest diagnostic accuracy for favourable treatment response with diffusion weighted imaging. T2 weighted volumetry had a limited additional diagnostic value and dynamic contrast enhanced imaging showed no additional diagnostic value to diffusion weighted imaging. In conclusion, this thesis showed the good predictive potential of functional MR imaging for favourable pathological response in locally advanced rectal cancer. Diffusion weighted imaging is most promising in response assessment and should be introduced in daily clinical practice for rectal cancer at this moment. This is the only way in which knowledge and experience can be obtained In order to be able to use the technique for selection of patients for organ-sparing treatments in rectal cancer in the near future.