Variations in the contouring of organs at risk: test case from a patient with oropharyngeal cancer.
OBJECTIVE
Anatomy contouring is critical in radiation therapy. Inaccuracy and variation in defining critical volumes will affect everything downstream: treatment planning, dose-volume histogram analysis, and contour-based visual guidance used in image-guided radiation therapy. This study quantified: (1) variation in the contouring of organs at risk (OAR) in a clinical test case and (2) corresponding effects on dosimetric metrics of highly conformal plans.


METHODS
A common CT data set with predefined targets from a patient with oropharyngeal cancer was provided to a population of clinics, which were asked to (1) contour OARs and (2) design an intensity-modulated radiation therapy plan. Thirty-two acceptable plans were submitted as DICOM RT data sets, each generated by a different clinical team. Using those data sets, we quantified: (1) the OAR contouring variation and (2) the impact this variation has on dosimetric metrics. New technologies were employed, including a software tool to quantify three-dimensional structure comparisons.


RESULTS
There was significant interclinician variation in OAR contouring. The degree of variation is organ-dependent. We found substantial dose differences resulting strictly from contouring variation (differences ranging from -289% to 56% for mean OAR dose; -22% to 35% for maximum dose). However, there appears to be a threshold in the OAR comparison metric beyond which the dose differences stabilize.


CONCLUSIONS
The effects of interclinician variation in contouring organs-at-risk in the head and neck can be large and are organ-specific. Physicians need to be aware of the effect that variation in OAR contouring can play on the final treatment plan and not restrict their focus only to the target volumes.
Canis Lupus LLC, Merrimac, WI, USA.
Benjamin E
BE
Nelms
Wolfgang A
WA
Tomé
Greg
G
Robinson
James
J
Wheeler
D001921:Brain / Q000000981:diagnostic imaging; D001933:Brain Stem / Q000000981:diagnostic imaging; D006801:Humans; D008334:Mandible / Q000000981:diagnostic imaging; D015588:Observer Variation; D058958:Organs at Risk / Q000000981:diagnostic imaging*; D009959:Oropharyngeal Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D010306:Parotid Gland / Q000000981:diagnostic imaging; D011785:Quality Assurance, Health Care; D018787:Radiation Oncology; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D013116:Spinal Cord / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed