Washout on Delayed Post Contrast High Resolution Spoiled Gradient Echo MRI is a Sign of Residual Rectal Cancer after Neoadjuvant Therapy

Motivation: Rectal cancer response assessment criteria utilize T2-weighted and diffusion-weighted images. High-resolution dynamic and delayed post-contrast images with gadolinium-based contrast are not used. Goal(s): Assess the value of gadolinium washout on delayed post-contrast T1 weighted images to predict residual cancer. Approach: In 34 patients with at least T2N0 rectal cancer pre-treatment, we compared the gadolinium washout on T1-weighted images during neoadjuvant therapy with the 1-year outcome after surgery or surveillance. Results: The presence of gadolinium washout on delayed post-contrast images obtained 4-12 weeks after radiation and 4-12 weeks after completion of total neoadjuvant therapy has a 100% positive predictive value for residual rectal cancer. Impact: Gadolinium washout may be useful in conjunction with T2-weighted and diffusion-weighted images for accurate assessment of rectal cancer treatment response.