Author: Stephen D. Davis, Alonso N. Gutierrez, Noah S. Kalman, Michael Leyva, Alejandro Rene Llanes Lopez, William Romaguera, Ranjini P. Tolakanahalli, Deborah Wang 👨🔬
Affiliation: Miami Cancer Institute, Baptist Health South Florida, Miami Cancer Institute, Miami Cancer Institute, Baptist Health 🌍
Purpose: To evaluate whether a modulated electron bolus (MEB) technique improves both nominal and shifted dose distributions in nasal electron therapy as compared to a non‑modulated, uniform‑thickness bolus technique (Simple).
Methods: Five nasal electron patients were each planned with MEB and Simple bolus designs using Adaptiiv 3D Bolus software under identical beam settings. Thirteen isocenter shifts (nominal plus ±3 mm and ±5 mm in x, y, and z) were assessed per plan. For each scenario, target coverage (D95) and hotspot metrics (D0.03cc) were collected. Additionally, nominal plans (zero isocenter shift) were compared. A One-sided Wilcoxon test assessed whether MEB dosimetrically outperformed Simple across all shifts, and Pearson correlations examined correlations of shift magnitudes (3 mm vs. 5 mm) . A repeated-measures ANOVA further analyzed coverage by plan type and shift magnitude.
Results: For nominal plans, mean D95 for the five patients was 100.4% for MEB vs. 96.4% for Simple. Maximum D0.03cc averaged 116.2% (MEB) vs. 120.6% (Simple). When all ±3 mm and ±5 mm shifts were analyzed, one-sided Wilcoxon tests showed significantly higher overall D95 in MEB (p=0.0095) and significantly lower D0.03cc in MEB (p=0.0095). Shift magnitude alone did not correlate with changes in D95 or D0.03cc (p>0.05) indicative that the direction of misalignment is more influential than the distance. Although the repeated-measures ANOVA did not find a main effect for technique (p=0.078) after averaging over shift magnitudes, the per-scenario paired comparisons favored MEB for D95 or D0.03cc.
Conclusion: In this cohort of five nasal electron therapy patients, the modulated bolus consistently provided higher nominal coverage, reduced nominal hotspots, and maintained superior dose metrics under ±3 mm and ±5 mm shifts compared to a non‑modulated bolus. These findings suggest that adopting a modulated electron bolus may enhance plan robustness and dose uniformity for nasal electron treatments.