Date Published: February 3, 2017
Publisher: Springer US
Author(s): Miriam M. van Heeswijk, Doenja M. J. Lambregts, Monique Maas, Max J. Lahaye, Z. Ayas, Jos M. G. M. Slenter, Geerard L. Beets, Frans C. H. Bakers, Regina G. H. Beets-Tan.
The 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.
Thirty-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.
Median 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.
When 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.
The primary aim of this study was to assess the feasibility of calculating ADC values of rectal tumors at the time of primary staging using non-precise rectal tumor delineation combined with histogram analysis as an alternative to precise manual tumor delineation, aiming to simplify and speed up the delineation process. Precise volumetric delineation (typically performed by manual tracing of the tumor boundaries by expert readers) is the most commonly used method in current literature to calculate mean tumor ADCs and therefore in a way considered the current ‘standard of reference’ method. The benefit of a non-precise delineation (e.g., simply placing a circular ROI with a margin around the tumor area) is that it is faster and can be performed by non-experienced readers. The main drawback, however, is that tissues other than tumor such as the normal rectal wall, perirectal fat, and adjacent organs will be included in the delineation, which will affect the mean ADC. Our hypothesis was that this effect may be overcome by adding histogram analysis to filter out these effects and specifically focus on ADC values of the tumor within the histogram in order to acquire similar ADCs as would have normally been derived by calculating the mean ADC from a precise delineation.