Monitoring early changes in rectal tumor morphology and volume during 5 weeks of preoperative chemoradiotherapy - An evaluation with sequential MRIs

Purpose: To assess early changes in rectal tumor volume and morphology on sequential MRIs performed during 5 weeks of chemoradiotherapy.

Materials and methods: Thirteen patients underwent weekly T2W-MRI during 5 weeks of preoperative radiotherapy (total 50 Gy), starting after the first week of radiation. Two radiologists visually evaluated tumor volume and morphology and one reader manually segmented tumors for each time point to quantitatively calculate tumor volumes. Evolution in tumor volume/morphology was assessed over time and compared between good responders (tumor regression grade (TRG) 1-2) and poor responders (TRG 3-5).

Results: Tumor volumes decreased significantly during radiation. Early signs of response were also visually apparent: in the majority of good responders an early fibrotic transformation (week 2-3) as well as a visually estimated early volume reduction of >1/3 (week 1-2), was observed while these early changes only occurred in a minority of poor responders.

Conclusion: Results of this exploratory pilot study suggest that changes in rectal tumor morphology (fibrosis) and volume can already be observed early during radiation, both when measured quantitatively and when assessed visually. These changes appear to be indicative of the final treatment outcome.