Radiobiological Effects for Prostate Cancer High-Dose-Rate Brachytherapy
Abstract
Background: HDR brachytherapy represents a cornerstone in prostate cancer management by enabling high tumor doses while sparing surrounding normal tissues. Radiobiological modelling allows quantitative assessment of tumour control and normal tissue complication probability for optimization of fractionation schedules. Objective: The purpose of this study is to comparatively appraise the radiobiological outcome of two HDR brachytherapy regimens, 13.5 Gy × 2 fractions versus 15 Gy × 1 fraction, regarding tumor control probability, normal tissue complication probability, and dose-effect metrics in patients presenting with intermediate- to high-risk prostate cancer. Materials and Methods: A retrospective analysis of 20 patients treated by Co-60 HDR brachytherapy was performed. The treatment planning was image-based, in which, target and organ-at-risk delineation was followed standard guidelines. BED, EQD2, and Deff were computed using the linear-quadratic model. TCP and NTCP modeling utilized Poisson-based and Lyman–Kutcher–Burman methods, respectively. Correlations between radiobiological parameters and TCP/NTCP were analyzed. Results: The single 15 Gy fraction regimen resulted in significantly higher BED, EQD2, Deff, and modeled TCP compared with 13.5 Gy×2 fractions (p ≤ 0.031). However, NTCP for urethra at 10% volume was higher in the 15 Gy group (8.42% ± 1.58 vs. 6.86% ± 1.24; p = 0.006). Strong positive correlations were observed between BED, EQD2, Deff and TCP (ρ = 0.984–1.000; p < 0.001). NTCP at 30% urethral volume negatively correlated with BED, EQD2, and Deff (ρ ≈ -0.52; p = 0.003). Conclusions: Higher radiobiological doses (BED, EQD2, Deff) in prostate HDR brachytherapy are strongly associated with improved tumor control, with Deff showing perfect correlation with TCP. A single 15 Gy fraction yields greater radiobiological effectiveness than 13.5 Gy × 2. Urethral toxicity shows no clear correlation at 10% volume but a strong negative correlation at 30%, indicating that higher doses may reduce toxicity at this level. Radiobiological modeling is thus valuable for optimizing HDR planning, enhancing tumor control prediction, and balancing urethral toxicity.
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