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. 2012 Mar 13:7:32.
doi: 10.1186/1748-717X-7-32.

3D Variation in delineation of head and neck organs at risk

Charlotte L Brouwer  1 , Roel J H M Steenbakkers, Edwin van den Heuvel, Joop C Duppen, Arash Navran, Henk P Bijl, Olga Chouvalova, Fred R Burlage, Harm Meertens, Johannes A Langendijk, Aart A van 't Veld
Affiliations

3D Variation in delineation of head and neck organs at risk

Charlotte L Brouwer et al. Radiat Oncol. .

Abstract

Background: Consistent delineation of patient anatomy becomes increasingly important with the growing use of highly conformal and adaptive radiotherapy techniques. This study investigates the magnitude and 3D localization of interobserver variability of organs at risk (OARs) in the head and neck area with application of delineation guidelines, to establish measures to reduce current redundant variability in delineation practice.

Methods: Interobserver variability among five experienced radiation oncologists was studied in a set of 12 head and neck patient CT scans for the spinal cord, parotid and submandibular glands, thyroid cartilage, and glottic larynx. For all OARs, three endpoints were calculated: the Intraclass Correlation Coefficient (ICC), the Concordance Index (CI) and a 3D measure of variation (3D SD).

Results: All endpoints showed largest interobserver variability for the glottic larynx (ICC = 0.27, mean CI = 0.37 and 3D SD = 3.9 mm). Better agreement in delineations was observed for the other OARs (range, ICC = 0.32-0.83, mean CI = 0.64-0.71 and 3D SD = 0.9-2.6 mm). Cranial, caudal, and medial regions of the OARs showed largest variations. All endpoints provided support for improvement of delineation practice.

Conclusions: Variation in delineation is traced to several regional causes. Measures to reduce this variation can be: (1) guideline development, (2) joint delineation review sessions and (3) application of multimodality imaging. Improvement of delineation practice is needed to standardize patient treatments.

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Figures

Figure 1
Figure 1
Division of the studied OARs in sub regions for studying the regional 3D variations in delineation. (a) Left side- (left), frontal (middle) and rear (right) 3D view of the studied organs at risk (OARs); the parotid and submandibular glands, spinal cord, thyroid cartilage and glottic larynx, divided in sub regions according to the colour legend. (b-f) Transverse central slices of the parotid gland (b), submandibular gland (c), glottic larynx (d), thyroid cartilage (e) and spinal cord (f) showing the division in sub regions according to the colour legend.
Figure 2
Figure 2
Variation in the definition of organ at risk volume. Volumes of the organs at risk according to observer 1(○), 2(□), 3(×), 4(Δ) and 5 (+). CTplan is planning CT and CTrep is repeat CT scan. The right parotid gland data contains 5 patients instead of 6 because of the exclusion of one gland (of patient 4) due to tumour infiltration.
Figure 3
Figure 3
Delineation variation of a parotid gland and a glottic larynx. Left parotid gland and glottic larynx delineations in a typical cranial (a and d), central (b and e) and caudal (c and f) transverse CT slice. Each colour corresponds to one observer.
Figure 4
Figure 4
3D delineation variation of a spinal cord, a right parotid and submandibular gland. 3D Standard Deviations (SDs) for a typical patient plotted in colour scale on the median contour surface of the organ. Note the different scalings. Spinal cord (a), right parotid gland (b) and right submandibular gland (c), frontal view.
See this image and copyright information in PMC

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