Deformable image registration accuracy: impact of user-defined parameter selection on contour propagation for deep inspiration breath-hold and free breathing breast radiotherapy.

Abstract

PurposeDeformable Image Registration (DIR) is increasingly used in breast radiotherapy planning, but the impact of different parameter settings on clinical accuracy remains unclear. This study systematically evaluates how focus region selection and registration direction affect DIR performance, providing evidence-based recommendations for clinical implementation.Materials and methodsWe analyzed 73 patients with left-sided breast cancer who underwent both free breathing (FB) and deep inspiration breath-hold (DIBH) planning CT scans. Clinical target volume (CTV), heart, left anterior descending artery, and both lungs were retrospectively contoured by one radiation oncologist on both datasets. Deformable Image Registration was performed bidirectionally (FB↔DIBH) using four different approaches: no focus region, CTV-focused, heart-focused, and surgical clip-focused registration. Volume differences and Dice Similarity Index (DSI) were calculated to assess registration accuracy. Generalized estimating equations analyzed possible correlations.ResultsFocus region selection critically impacted DIR accuracy. CTV-focused registration achieved highest CTV overlap (DSI: 0.96 vs. 0.91 without focus, p ConclusionDIR performance in breast radiotherapy is highly dependent on user-defined parameters, with no single configuration optimizing all structures simultaneously. Focus region selection creates a trade-off between local accuracy and global registration quality. Clinical implementation requires structure-specific parameter optimization and mandatory manual review. These findings establish practical limitations and benefits of hybrid DIR algorithms for breast radiotherapy workflows and highlight the continued necessity of expert oversight.