Clinical feasibility of atlas-based auto-segmentation for organ-at-risk contouring in head-and-neck radiotherapy.

PURPOSE: Head-and-neck (HN) contouring presents significant challenges due to the complex anatomy of the region and the proximity of organs-at-risk (OARs) to the target. Manual contouring is time-consuming, labor-intensive, and prone to inter- and intra-observer variability. Additionally, contours delineated prior to treatment may not accurately reflect the patient's anatomy over the extended treatment course. This study explores the feasibility of using auto-generated OAR contours in HN planning.

METHODS

A retrospective study was conducted on 20 patients, each with a planning CT and 35 CBCT images. OARs were manually delineated and automatically generated using atlas-based segmentation algorithms on planning CTs. Treatment plans were created via a novel two-step optimization process, incorporating a knowledge-based planning solution for both auto-generated (aOAR-plan) and manual OARs (mOAR-plan). The accuracy of auto-generated contours was quantified using the overlap index (OI) and dose similarity coefficient (DSC). Planning dose comparisons were performed between aOAR- and mOAR-plans. Additionally, planning doses were transferred from CT to CBCTs based on clinical shifts, and contour-based deformable registration was employed to calculate cumulative doses. Cumulative dose evaluations were performed for serial organs and parallel organs that can be fully imaged within the CBCT field.

RESULTS

For OARs located farther from the target, even though atlas-based segmentation could not accurately reproduce patient anatomy, excellent agreement in planning doses was observed between the aOAR- and mOAR-plans. The average OI/DSC between manual and auto-generated contours were 85.0% ± 5.4%/87.4% ± 2.6% for the larynx, 76.0% ± 9.3%/77.0% ± 5.8% for the pharynx, 89.9% ± 4.0%/87.8% ± 2.5% for the oral cavity, 81.5% ± 10.5%/78.2% ± 5.9% and 83.2% ± 10.6%/77.8% ± 7.5% for the left and right parotid, respectively. The cumulative dose differences for OARs between aOAR- and mOAR-plans were within 2 Gy for 90% of patients studied.

CONCLUSION

Automated-contouring tools offer improvement in contour consistency, provide acceptable doses compared with manually drawn contours in HN radiotherapy.