Reproducibility in contouring the neurovascular bundle for prostate cancer radiation therapy.

PURPOSE: Efforts to define the neurovascular bundle (NVB) for prostate radiation have varied. In this series, we sought to determine the reproducibility and reliability of contouring the classical posterolateral NVB on dedicated pelvic magnetic resonance imaging (MRI) scans.

METHODS AND MATERIALS: A total of 120 NVB structures were defined on 10 3-Tesla pelvic MRI scans in patients with prostate cancer but without extraprostatic extension. One pelvic radiologist served as the expert in contouring the right and left NVB for each case. Five radiation oncologists, with varying levels of experience, contoured the right and left NVBs on these same cases. The intraclass correlation coefficient across each rater and the expert, Pearson correlation coefficient between each rater and the expert, and the Dice similarity coefficient (DSC) between each rater and the expert were calculated to evaluate contour agreement and overlap.

RESULTS: The overall intraclass correlation coefficient was 0.89 (95% confidence interval [CI], 0.81-0.95). The Pearson correlation coefficient was 0.95 (95% CI, 0.86-0.98) for rater 1, 0.98 (95% CI, 0.95-0.99) for rater 2, 0.94 (95% CI, 0.86-0.98) for rater 3, 0.98 (95% CI, 0.95-0.99) for rater 4, and 0.84 (95% CI, 0.63-0.93) for rater 5. The mean DSC was 0.72 (standard deviation [SD], 0.07) for rater 1, 0.72 (SD, 0.06) for rater 2, 0.73 (SD, 0.09) for rater 3, 0.74 (SD, 0.09) for rater 4, and 0.68 (SD, 0.13) for rater 5. Overall, across all raters, the average DSC was 0.72 (SD, 0.09).

CONCLUSIONS: The classic posterolateral NVB can be accurately and reliably contoured on 3-Tesla pelvic MRI scans by radiation oncologists.