Measuring the apparent diffusion coefficient in primary rectal tumors: is there a benefit in performing histogram analyses?

Miriam M. van Heeswijk,Monique Maas,Doenja M. J. Lambregts,Regina G. H. Beets-Tan,Max J. Lahaye,Jos M. G. M. Slenter,Geerard L. Beets,Frans C. H. Bakers,Z. Ayas

doi:10.1007/s00261-017-1062-2

Abstract

PurposeThe apparent diffusion coefficient (ADC) is a potential prognostic imaging marker in rectal cancer. Typically, mean ADC values are used, derived from precise manual whole-volume tumor delineations by experts. The aim was first to explore whether non-precise circular delineation combined with histogram analysis can be a less cumbersome alternative to acquire similar ADC measurements and second to explore whether histogram analyses provide additional prognostic information.MethodsThirty-seven patients who underwent a primary staging MRI including diffusion-weighted imaging (DWI; b0, 25, 50, 100, 500, 1000; 1.5 T) were included. Volumes-of-interest (VOIs) were drawn on b1000-DWI: (a) precise delineation, manually tracing tumor boundaries (2 expert readers), and (b) non-precise delineation, drawing circular VOIs with a wide margin around the tumor (2 non-experts). Mean ADC and histogram metrics (mean, min, max, median, SD, skewness, kurtosis, 5th–95th percentiles) were derived from the VOIs and delineation time was recorded. Measurements were compared between the two methods and correlated with prognostic outcome parameters.ResultsMedian delineation time reduced from 47–165 s (precise) to 21–43 s (non-precise). The 45th percentile of the non-precise delineation showed the best correlation with the mean ADC from the precise delineation as the reference standard (ICC 0.71–0.75). None of the mean ADC or histogram parameters showed significant prognostic value; only the total tumor volume (VOI) was significantly larger in patients with positive clinical N stage and mesorectal fascia involvement.ConclusionWhen performing non-precise tumor delineation, histogram analysis (in specific 45th ADC percentile) may be used as an alternative to obtain similar ADC values as with precise whole tumor delineation. Histogram analyses are not beneficial to obtain additional prognostic information.

Highlights

The apparent diffusion coefficient (ADC) is a potential prognostic imaging marker in rectal cancer
Its value has been demonstrated in the restaging setting to assess the response of the primary tumor to neoadjuvant chemoradiotherapy (CRT) and determine whether or not a residual tumor mass is still present within the post-radiation fibrosis [1,2,3]
In research settings, several studies have shown that quantifying the diffusion of rectal tumors by measuring the apparent diffusion coefficient (ADC) may be used as an imaging biomarker

Summary

Introduction

The apparent diffusion coefficient (ADC) is a potential prognostic imaging marker in rectal cancer. In research settings, several studies have shown that quantifying the diffusion of rectal tumors by measuring the apparent diffusion coefficient (ADC) may be used as an imaging biomarker This could be beneficial in clinics to predict prognostic factors such as nodal stage, mesorectal fascia (MRF) involvement, and histological differentiation grade [5,6,7,8]. ADC values are most often expressed as the mean ADC, which can be acquired either from a single tumor slice [14, 15], from tumor sample measurements [3, 5], or by manually delineating the whole tumor volume on the diffusion-weighted images [1, 12, 16, 17] The latter approach is most commonly advocated and has been shown to provide the most reproducible results [18, 19]. A labor-intensive and time-consuming method, which is one of the factors that hamper the translation of the use of quantitative ADC measures from research settings to clinical practice

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