Value of percent change in tumoral volume measured at T2-weighted and diffusion-weighted MRI to identify responders after neoadjuvant chemoradiation therapy in patients with locally advanced rectal carcinoma

Purpose: To evaluate the percent change in tumoral volume measured at T2-weighted magnetic resonance imaging (T2WMRI) and diffusion-weighted (DWI) as a method to identify responders after chemo- and radiation therapy (CRT) in patients with locally advanced rectal carcinoma. Materials and Methods: Forty-five consecutive patients (mean age ± SD: 72 years ± 9.7; male/female = 24/21) with locally advanced rectal carcinoma underwent CRT followed by surgery. Each patient underwent T2WMRI and DWI at 1.5T before and 6 weeks after the completion of CRT. The percent change in tumoral volume before and 6 weeks after CRT was compared in patients classified as responders and nonresponders according to rectal cancer regression grade. Results: Twenty-five patients were classified as responders with either partial (n = 20) or complete response (n = 5), while 20 patients were classified as nonresponders due to stable disease (n = 18) or disease progression (n = 2). Responders vs. nonresponders differed in the percent change of tumoral volume at T2WMRI (−67% ± 26% vs. −29% ± 26%; P < 0.05) and DWI images (−72% ± 24% vs. −33% ± 28%; P < 0.05) with a cutoff ≤ −70% for T2WMRI (sensitivity = 69%, 95% confidence interval [CI]: 48−85%; specificity = 100%, 95% CI 81–100%) and ≤66% for DWI (sensitivity = 73%, 95% CI: 52–88%; specificity = 100%, 95% CI 81–100%). Conclusion: The percent change in tumoral volume at T2WMRI and DWI images can differentiate responders from nonresponders in patients with locally advanced rectal carcinoma after neoadjuvant CRT.