Deformable Dose Accumulation Evaluation with Spatial Corrective Guidance Using Subregion Analysis
Abstract
Purpose
Modern radiation therapy increasingly requires deforming prior dose to new CT scans for re-irradiation. Current validation methods report whole-organ agreement but lack spatial specificity and corrective guidance. This study developed a subregion evaluation tool that localizes errors and directs targeted corrections independent of the deformation.
Methods
The tool subdivides organs into axial levels and angular sectors based on fractional position within each contour, ensuring independence from the deformation vector field. For each subregion, signed dose error is computed between deformed and original distributions. Analysis of axial profiles along the organ length identify which levels contain errors, then angular profiles within each level pinpoint circumferential location. The signed error pattern reveals regional errors of opposite directions that cancel in whole-organ averaging. We compared maximum subregion error to conventional whole-organ mean dose difference and quantified the proportion of subregion error magnitude hidden by this cancellation. We applied the tool using 5 axial levels and 4 angular sectors to 106 esophageal dose pairs from a re-irradiation cohort. Cases exceeding 10 Gy maximum subregion error were flagged.
Results
Of 106 cases, 21 were flagged. Maximum subregion error magnitudes were 8-fold larger than whole-organ values (median 3.4 vs 0.4 Gy). A median 56% (IQR 29-81%) of subregion error magnitude was masked by error cancellation. Dice coefficient showed no significant difference between flagged and passed groups (p=0.75). Cases with similar Dice (0.70±0.01, n=11) had maximum subregion error ranging 0.2-12.2 Gy. In 67% of flagged cases, ≥50% of error magnitude concentrated in ≤3 subregions, localizing errors for targeted review.
Conclusion
This tool bridges geometric validation and dosimetric accuracy verification, enabling physicists to identify error locations and guide clinical review of deformable dose accumulation. Studies and re-treatments relying on deformable dose should consider such spatial validation to ensure accurate assessment of deformed prior doses.