Functional Imaging Predictors of Response to Chemoradiation

Abstract

Early prediction of response to chemoradiotherapy in locally advanced rectal cancer has the potential to minimize surgical intervention in patients with complete response, while allowing non-responding patients to explore more aggressive treatments. Functional imaging detection of tumoral microstructural and metabolic changes presents a valuable tool for preoperative chemoradiation response assessment. Diffusion-weighted MRI has increasingly been incorporated into study protocols, with the apparent diffusion coefficient largely found to be the most robust global predictor of neoadjuvant therapy response. However, no definitive predictive biomarkers have been identified, with inconsistent results across all imaging modalities. We evaluated the pros and cons of PET/CT imaging; perfusion imaging; and diffusion-weighted, dynamic contrast-enhanced, multiparametric, and low-field functional MRI in the early prediction of response to chemoradiotherapy. Future directions of study include combinatorial imaging with both MRI and PET/CT modalities and further investigation of on-board low-field MRI imaging during radiotherapy treatment delivery.