Fecal incontinence and radiation dose on anal sphincter in patients with locally advanced rectal cancer (LARC) treated with preoperative chemoradiotherapy: a retrospective, single-institutional study.

BACKGROUND: The objective of the study is to determine the correlations among the variables of dose and the sphincter function (SF) in patients with locally advanced rectal cancer treated with preoperative capecitabine/radiotherapy followed by low anterior resection (LAR) + TME.

METHODS: We retrospectively reviewed 92 consecutive patients with LARC treated at our center with LAR from 2006 and more than 2 years free from disease. We re-contoured the anal sphincters (AS) of patients with the help of the radiologist. SF was assessed with the Wexner scale (0-20 points, being punctuation inversely proportional to annal sphincter functionality). All questionnaires were filled out between January 2010 and December 2012. Dosimetric parameters that have been studied include V 20 , V 30 , V 40 , V 50 , mean dose (D mean ), minimum dose (D min ), D 90 (dose received by 90% of the sphincter) and D 98 .

STATISTICAL ANALYSIS: The correlations among the variables of dose and SF were studied by the Spearman correlation coefficient. Differences in SF relating to maximum doses to the sphincter were assessed by the Mann-Whitney test.

RESULTS: Mean Wexner score was 5.5 points higher in those patients with V 20  > 0 compared to those for which V 20  = 0 (p = 0.008). In a multivariate regression model, results suggest that the effect of V 20 on poor anal sphincter control is independent of the effect of distance, with an adjusted OR of 3.42.

CONCLUSIONS: In order to improve the SF in rectal cancer treated with preoperative radiotherapy/capecitabine followed by conservative surgery, the maximum radiation dose to the AS should be limited, when possible, to <20 Gy.