Dosimetry modeling for focal high-dose-rate prostate brachytherapy

Area of Science:

• Radiation Oncology
• Medical Physics
• Urologic Oncology

Background:

• High-dose-rate (HDR) prostate brachytherapy is a primary treatment for localized prostate cancer.
• Optimizing dose delivery while minimizing toxicity to surrounding organs is crucial for treatment success.

Purpose of the Study:

• To compare the dosimetry of whole-gland (WG), hemi-gland (HEMI), and ultra-focal (UF) HDR prostate brachytherapy plans.
• To assess the impact of source position errors and utilize Monte Carlo (MC) simulations for dosimetric analysis.

Main Methods:

• Delineation of tumor volumes from MRI and biopsy for 9 patients.
• Creation of WG, HEMI, and UF treatment plans for 19 Gy single fraction monotherapy.
• Assessment of plan robustness to systematic source position shifts (1-4 mm).
• MC simulations to evaluate the dosimetric impact of steel catheters.

Main Results:

• HEMI and UF plans achieved higher D90 and V100 values for the target volumes compared to WG plans.
• Significant reductions in urethra and rectal dose were observed with HEMI and UF plans (e.g., rectal D2cc: 12.5 Gy for WG vs. 4.6 Gy for UF).
• Focal plans (UF) showed increased sensitivity to source position errors, with a 2 mm shift reducing F-PTV D90 by 8.3%.

Conclusions:

• HEMI and UF HDR prostate brachytherapy can deliver superior target coverage (D90) with lower organ-at-risk doses compared to WG treatments.
• Focal treatment strategies necessitate careful attention to source positioning due to increased sensitivity to positional errors.
• MC simulations confirmed the dosimetric accuracy across all plan types, with minimal impact (<2%) on DVH parameters from catheters.