Biologically Optimized Intensity-Modulated Brachytherapy for Prostate Cancer: Homogeneous Vs. Heterogeneous Focal Boosting
Abstract
Purpose
To investigate the feasibility and potential benefits of biologically optimised treatment planning (BiRT) utilizing heterogeneous focal-boost prescriptions based on patient-specific cell density distributions. This study compares conventional high-dose-rate brachytherapy (BT) against Intensity-Modulated Brachytherapy (IMBT). IMBT is a novel technique that employs dynamic shielding within applicators to achieve rotational source modulation, generating highly conformal dose distributions for preferential tumour targeting and organ-at-risk (OAR) sparing.
Methods
Three high-risk prostate cancer patients with varying dominant intra-prostatic lesion (DIL) volumes (small, medium, large) were selected from a larger cohort. Voxel-wise tumour cell distribution maps were derived from annotated histology. Four Monte Carlo-based plans were generated for each patient: homogeneous and heterogeneous (BiRT) DIL boosts using both conventional BT and IMBT. Plans were evaluated based on tumour control probability (TCP) and urethral and rectal dosimetry.
Results
The IMBT-BiRT approach achieved the highest TCP for all patients. While heterogeneous boosting generally improved TCP compared to homogeneous plans, conventional BT plans were restricted by urethral dose constraints. IMBT plans achieved significantly lower (P < 0.05) urethra D30 and D10 values compared to BT. The most substantial TCP enhancement using IMBT-BiRT was observed in the patient with the largest DIL volume.
Conclusion
IMBT-BiRT achieved the highest predicted TCP while simultaneously reducing urethral doses compared to conventional BT. Due to its ability to overcome anatomical constraints through superior OAR sparing, IMBT is identified as the most suitable modality for delivering heterogeneous DIL boosts.