Abstract
BackgroundConsistent 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.MethodsInterobserver 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).ResultsAll 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.ConclusionsVariation 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.
Highlights
Consistent delineation of patient anatomy becomes increasingly important with the growing use of highly conformal and adaptive radiotherapy techniques
For the glottic larynx and spinal cord observer 1 seem to define the smallest volumes while observer 5 defines the largest volumes (Friedman Test, p < 0.006)
These results were in line with the mean organs at risk (OARs) ratios (Table 1)
Summary
Consistent delineation of patient anatomy becomes increasingly important with the growing use of highly conformal and adaptive radiotherapy techniques. Radiotherapy (RT) plays an important role in the treatment of head and neck cancer patients. Variation in contouring is an important obstacle in the development of high geometric accuracy in the clinical application of these new techniques. Reproducibility in delineation of tumour and normal structures is of importance for optimal patient treatment [1]. As new radiation delivery techniques are increasingly controlled by OAR constraints for normal tissue sparing [2], variations in OAR delineation may unintentionally influence the treatment plan including the dose to these OARs [3]. In a number of publications (e.g. Bortfeld and Jeraj [4]), uncertainties in the contouring of organs is mentioned as one of the potential causes for uncertainties in historical dose and volume data and reduced performance of predictive models. Deasy et al [5] mentioned that differences in segmentation procedure could be one of the reasons explaining variations between existing models
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