Value of percent change in tumoral volume measured at T 2 ‐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 T 2 ‐weighted magnetic resonance imaging ( T 2 WMRI) 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 T 2 WMRI 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 T 2 WMRI (−67% ± 26% vs. −29% ± 26%; P < 0.05) and DWI images (−72% ± 24% vs. −33% ± 28%; P < 0.05) with a cutoff ≤ −70% for T 2 WMRI (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 T 2 WMRI and DWI images can differentiate responders from nonresponders in patients with locally advanced rectal carcinoma after neoadjuvant CRT. J. Magn. Reson. Imaging 2016;44:1415–1424.