S33
Brachytherapy - General brachytherapy
ESTRO 2026
kinetics to calculate spatially-resolved BED accounting for realistic delivery sequences. Material/Methods: We extracted structures, HDR dwell positions and times from RT Plan DICOM files and reconstructed 4D dose matrices (3D space + time) using a single-source reference approach. A normalized dose-rate template from one dwell position was iteratively translated and scaled for all dwell positions, incorporating actual dwell times and inter-catheter transit times. A voxel level G factor was computed using a multi-phasic repair pathway selection depending on dose rate, damage complexity, and temporal patterns. The framework was tested on clinical cases: prostate implants (small/medium/large volumes) and breast interstitial cases, comparing conventional instantaneous BED versus temporal repair-corrected BED for various applicator order delivery sequences. Results: Temporal dose reconstruction revealed (Figure 1) substantial spatial BED heterogeneity not captured by conventional calculations. G-factors (repair correction) ranged from 0.65-0.96 within individual cases, with early-treated regions showing 15-20% BED reduction compared to instantaneous assumptions. Large implants with low source activity demonstrated the most pronounced effects, with mean BED reductions of 18-27% in peripheral target regions due to extended treatment times (>15 minutes) allowing significant repair. Prostate cases showed systematic spatial patterns: base regions (treated early) exhibited lower biological effectiveness than apex regions (treated late). Breast interstitial cases with longer delivery sequences (>20 minutes) showed BED reductions exceeding 25% in some subvolumes. A prostate example is shown in Figure.2. An actual treatment with 17 catheters delivered 13.5Gy in
Conclusion: Individual customization of commercial applicators for brachytherapy using clinically approved and readily- available disposable medical materials is a feasible strategy with an acceptable radiation toxicity and complication profile in patients for whom an adequate dose coverage is not achievable using unmodified commercial applicators. Keywords: Personalized applicators Temporal dose delivery reconstruction enables voxel-wise DNA multipath repair modeling and spatially resolved BED calculation in HDR brachytherapy Dorin A Todor, Alfredo I Urdaneta Radiation Oncology, Virginia Commonwealth University, Richmond, USA Purpose/Objective: Current treatment planning systems (TPS) calculate biologically effective dose (BED) assuming Proffered Paper 1177 instantaneous dose delivery, ignoring DNA repair occurring during treatment. For high dose rate (HDR) brachytherapy, temporal dose delivery patterns vary dramatically across the target volume, with early- treated voxels experiencing different repair opportunities than late-treated regions. We developed a computational framework to reconstruct voxel-level temporal dose patterns from clinical DICOM files and using a multi-pathway (NHEJ, HR, Alt-NHEJ) repair
1033.0s. The loss of BED is very spatially heterogeneous, reaching as much as 28%.
Made with FlippingBook - Share PDF online