Variability of gross tumor volume delineation in head-and-neck cancer using CT and PET/CT fusion

Purpose: To assess the need for gross tumor volume (GTV) delineation protocols in head-and-neck cancer (HNC) treatment planning by use of positron emission tomography (PET)/computed tomography (CT) fusion imaging. Assessment will consist of interobserver and intermodality variation analysis. Methods and Materials: Sixteen HNC patients were accrued for the study. Four physicians (2 neuroradiologists and 2 radiation oncologists) contoured GTV on 16 patients. Physicians were asked to contour GTV on the basis of the CT alone, and then on PET/CT fusion. Statistical analysis included analysis of variance for interobserver variability and Student’s paired sample t test for intermodality and interdisciplinary variability. A Boolean pairwise analysis was included to measure degree of overlap. Results: Near-significant variation occurred across physicians’ CT volumes ( p = 0.09) and significant variation occurred across physicians’ PET/CT volumes ( p = 0.0002). The Boolean comparison correlates with statistical findings. One radiation oncologist’s PET/CT fusion volumes were significantly larger than his CT volumes ( p < 0.01). Conversely, the other radiation oncologist’s CT volumes tended to be larger than his fusion volumes ( p = 0.06). No significant interdisciplinary variation was seen. Significant disagreement occurred between radiation oncologists. Conclusion: Significant differences in GTV delineation were found between multiple observers contouring on PET/CT fusion. The need for delineation protocol has been confirmed.