Analyzing the Relationship between Dose and Geometric Agreement Metrics for Auto-Contouring in Head and Neck Normal...

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Planning

Background:

• Accurate contouring of organs-at-risk (OARs) is crucial for effective head and neck (H&N) cancer radiotherapy.
• Geometric agreement metrics (Dice Similarity Coefficient, Surface DSC, Hausdorff Distance) are commonly used to assess contour quality.
• The relationship between geometric agreement and dosimetric impact requires further investigation.

Purpose of the Study:

• To determine the correlation between geometric and dosimetric agreement metrics in H&N cancer radiotherapy plans.
• To evaluate if geometric indices accurately predict significant dosimetric differences in OARs.
• To assess the influence of proximity to the planning target volume (PTV) on this relationship.

Main Methods:

• Retrospective analysis of 287 H&N radiotherapy plans, comparing auto-contoured and clinically used contours.
• Evaluation using Dice Similarity Coefficient (DSC), surface DSC (sDSC), and Hausdorff Distance (HD).
• Analysis of OARs with dose differences (≥200 cGy) in Dmax and Dmean, examining proximity to PTV.

Main Results:

• 90% of 4995 contour pairs met geometric criteria (DSC ≥ 0.75, sDSC ≥ 0.86, HD < 7.65 mm).
• 95-96% of OARs had dosimetric differences <200 cGy for Dmax and Dmean.
• OARs with significant dose differences were often within 2.5 cm of the PTV, irrespective of geometric agreement.

Conclusions:

• Geometric agreement metrics serve as approximate indicators of contour quality and dosimetric discordance.
• A subset of OARs near the PTV may exhibit misleading geometric agreement, masking significant dosimetric variations.
• Clinical review remains essential, especially for OARs adjacent to the PTV, to ensure treatment plan accuracy.