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. 2012 Aug;85(1016):1070-7.
doi: 10.1259/bjr/32038456.

Interobserver variation in parotid gland delineation: a study of its impact on intensity-modulated radiotherapy solutions with a systematic review of the literature

S W Loo  1 , W M C Martin, P Smith, S Cherian, T W Roques
Affiliations

Interobserver variation in parotid gland delineation: a study of its impact on intensity-modulated radiotherapy solutions with a systematic review of the literature

S W Loo et al. Br J Radiol. 2012 Aug.

Abstract

Objectives: This study evaluates the interobserver variation in parotid gland delineation and its impact on intensity-modulated radiotherapy (IMRT) solutions.

Methods: The CT volumetric data sets of 10 patients with oropharyngeal squamous cell carcinoma who had been treated with parotid-sparing IMRT were used. Four radiation oncologists and three radiologists delineated the parotid gland that had been spared using IMRT. The dose-volume histogram (DVH) for each study contour was calculated using the IMRT plan actually delivered for that patient. This was compared with the original DVH obtained when the plan was used clinically.

Results: 70 study contours were analysed. The mean parotid dose achieved during the actual treatment was within 10% of 24 Gy for all cases. Using the study contours, the mean parotid dose obtained was within 10% of 24 Gy for only 53% of volumes by radiation oncologists and 55% of volumes by radiologists. The parotid DVHs of 46% of the study contours were sufficiently different from those used clinically, such that a different IMRT plan would have been produced.

Conclusion: Interobserver variation in parotid gland delineation is significant. Further studies are required to determine ways of improving the interobserver consistency in parotid gland definition.

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Figures

Figure 1
Figure 1
Diagrammatic representation of the Jaccard coefficient for two parotid delineations A and B. The Jaccard coefficient is defined as the ratio of the volume of intersection or the overlapping volume between A and B (A∩B) to the encompassing volume for A and B.
Figure 2
Figure 2
Graph showing the mean parotid doses obtained by radiation oncologists for all ten data sets.
Figure 3
Figure 3
Graph showing the mean parotid doses obtained by radiologists for all ten data sets.
Figure 4
Figure 4
Axial CT image showing the study contours of the seven observers for one parotid gland. (a) Radiologists; (b) radiation oncologists.
See this image and copyright information in PMC

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