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

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.