Interobserver Variability in the Delineation of Gross Tumour Volume and Specified Organs-at-risk During IMRT for Head and Neck Cancers and the Impact of FDG-PET/CT on Such Variability at the Primary Site.

Purpose: To assess interobserver variability (IOV) in the delineation of structures during intensity-modulated radiation therapy for head and neck squamous cell carcinoma and the impact of fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) on such variability at the primary site.

Methods: Three experienced head-neck radiation oncologists, blinded to each other, delineated the primary site gross tumour volume (GTV) and specified organs-at-risk (OARs) viz parotid gland, spinal cord, and cochlea in 10 patients with pharyngolaryngeal cancers suited for definitive intensity-modulated radiation therapy. IOV was assessed by concordance index (CI), Dice similarity coefficient (DSC), and Fleiss' kappa. Subsequently, the observers refined their corresponding GTVs incorporating information from FDG-PET/CT. The impact of FDG-PET/CT on variability of GTV was assessed by comparing the overlap indices with and without FDG-PET/CT using paired 't' test.

Results: There was moderate IOV in the delineation of GTV as evidenced by mean CI, DSC, and Fleiss' kappa of 0.41, 0.57, and 0.56, respectively. The use of FDG-PET/CT improved consistency of target volume delineation with resultant improvement in the overlap indices (mean CI, DSC, and Fleiss' kappa of 0.54, 0.69, and 0.69, respectively) that was statistically significant (P < .001). There was good agreement between the three observers for delineation of spinal cord and parotid glands. Concordance was worst for the cochlea.

Conclusion: This study demonstrates the presence of moderate IOV between three experienced head and neck radiation oncologists in an academic institutional setting for the delineation of GTV. The use of FDG-PET/CT for target volume delineation results in significant reduction of such variability.