Anatomy-Based Multivariate Model Predicts Boost Coverage Robustness of Dose-Escalated Simultaneous Integrated Boost Radiotherapy in Early Breast Cancer.

Abstract

PurposeThis study assessed dosimetric effects of setup errors on boost target volume (PTVboost) coverage using simultaneous integrated boost (SIB) in early-stage left-sided breast cancer.Methods35 patients who received whole-breast radiotherapy (40.0 Gy/15 Fr) combined with a SIB to the tumor bed (48.0 Gy/15 Fr) were retrospectively analyzed. Translational-rotational coupled errors (1.0°rotation paired with 1.0 mm translation, 2.0° with 2.0 mm, 3.0° with 3.0 mm) were simulated about all axes. The D95 (dose to 95% of the PTVboost) and V95 (volume covered by 95% of the prescribed dose) were assessed through multivariate analysis to explore the relationship between PTVboost coverage and various anatomy factors, including the volume of the PTVboost (V_boost), the distance from the PTVboost centroid to the isocentre (D_iso), the mean depth from the anterior edge of PTVboost to the body surface (S_Depth), and setup errors.ResultsUnder a combination of 1.0° rotation and 1.0 mm setup errors, the D95 values and V95 coverage of the PTVboost were ≥95% in all cases. However, when the error combination increased to 2.0°:2.0 mm, there was a significant decrease in coverage, with approximately 80% of the target areas exhibiting D95 and V95 values <95%. When the setup errors further increased to 3.0°:3.0 mm, D95 and V95 values were <95% in all cases. Multivariate analysis indicated that V_boost, D_iso, and S_Depth were significant predictors of target coverage.ConclusionPTVboost dose coverage risk were synergistically influenced by increasing D_iso, reduced V_boost, and shorter S_Depth. The multivariate model may stratify coverage risk categories using tumor anatomy and setup error magnitudes.