Author: Abby E. Besemer, Carolyn Eckrich, John M. Floberg, Michael J. Lawless, Jessica R. Miller, Joseph B. Schulz, Jordan M. Slagowski, Autumn E. Walter-Denzin 👨🔬
Affiliation: University of Wisconsin-Madison Department of Medical Physics, University of Wisconsin-Madison Department of Human Oncology, Department of Human Oncology, University of Wisconsin School of Medicine and Public Health, Department of Radiation Oncology, Stanford University School of Medicine, Department of Human Oncology, University of Wisconsin-Madison 🌍
Purpose: The aim of this treatment planning study was to evaluate the feasibility of escalating dose with HDR prostate brachytherapy to imaging-identified intraprostatic macroscopic lesions while modestly escalating dose to the entire prostate and strictly limiting dose to organs-at-risk (OARs) including the bladder, rectum, and urethra.
Methods: Fourteen patients treated with HDR prostate brachytherapy to 15 Gy in a single fraction were retrospectively analyzed. Target volumes and OARs were delineated on CT images fused with PSMA-PET and/or multiparametric MRI to identify intraprostatic lesions (gross tumor volume, GTV). Boost plans were generated to maximize GTV dose (D90%) while maintaining prostate planning target volume (PTV) coverage (V100%) and adhering to clinical OAR constraints (rectum and bladder V80% < 1 cm3, urethra V118% < 0.1 cm3). GTV dose coverage and OAR sparing were compared with the original clinical results. Statistical significance was assessed using a two-sided Wilcoxon sum rank test.
Results: Mean prostate V100% coverage was maintained, with no significant difference between re-optimized boost plans (mean 97.4% ± 1.5%) and clinical plans (97.5% ± 0.9%). Optimized boost plans significantly (p<0.05) increased dose to the GTV from 120.7% to 133.7% in terms of D90% while meeting all OAR constraints. Increases in GTV D90% ranged from 3.7% to 23.3%. Differences in bladder dose were not significant. Rectum and urethra doses significantly (p<0.05) increased but were less than the specified treatment planning constraints.
Conclusion: Selective dose escalation to intraprostatic lesions in CT-based HDR prostate brachytherapy is feasible and can significantly enhance GTV dose coverage without exceeding OAR dose limits. This approach may enable personalized dose intensification strategies to improve therapeutic outcomes while preserving treatment safety.