The purpose of this study was to correlate tumor volumetric analysis obtained using magnetic resonance (MR) imaging with disease-free survival in patients with advanced rectal cancer who underwent preoperative chemoradiotherapy (CRT).

Institutional review board approval was obtained and patient informed consent was waived. This study included 74 patients (47 men, 27 women; mean age, 64 years±10 [SD] years) who underwent preoperative CRT and subsequent rectal surgery between January 2007 and December 2010. Two radiologists who were blinded to the clinical outcome measured tumor volume separately on two sets of MR images obtained before and after CRT. Patients were classified into two groups according to the episode of recurrence and recorded disease-free survival. To assess factors relevant to disease-free survival, univariate and multivariate Cox regression analysis were performed for tumor volume reduction ratio, circumferential resection margin, tumor regression grade, and pathologic staging.

Tumor volume reduction ratio (P=0.009), circumferential resection margin (P=0.008) and tumor regression grade (P=0.002) were significantly associated with disease-free survival. At multivariate analysis, tumor volume reduction ratio was the single variable that was associated with disease-free survival (P=0.003). Tumor volume reduction ratio was also a reliable parameter with an excellent interobserver correlation between two readers for pre-CRT volume (ICC=0.939; 95%CI: 0.885–0.979; P<0.001) and post-CRT volume (ICC=0.889; 95%CI: 0.845–0.934; P<0.001).

MR volumetric measurement of rectal cancer helps predict disease-free survival in patients with rectal cancer who underwent preoperative CRT.