Dosimetry Modeling for Focal Low-Dose-Rate Prostate Brachytherapy

Area of Science:

• Oncology
• Radiation Oncology
• Medical Physics

Background:

• Whole-gland brachytherapy for prostate cancer can lead to significant side effects.
• Focal brachytherapy aims to reduce these side effects by targeting only the cancerous lesion(s).
• Optimal dosimetry for focal low-dose-rate (LDR) prostate brachytherapy requires investigation.

Purpose of the Study:

• To investigate optimal dosimetry for focal LDR prostate brachytherapy.
• To assess the impact of seed displacement and interseed attenuation (ISA) on focal brachytherapy plans.
• To evaluate treatment planning feasibility and organ-at-risk sparing for focal prostate brachytherapy.

Main Methods:

• Retrospective analysis of treatment plans (whole-gland, hemi-gland, ultra-focal) in nine patients.
• Utilized multiparametric magnetic resonance imaging (mp-MRI) and transperineal template prostate mapping (TPM) biopsy for targeting.
• Assessed plan robustness to seed displacement and ISA using Monte Carlo simulations.

Main Results:

• Ultra-focal (UF) plans used significantly fewer seeds (25) compared to whole-gland (WG) (81) and hemi-gland (hemi) (56) plans.
• UF plans achieved higher target D90 (218.3 Gy) and V100 (99.8%) compared to hemi and WG plans.
• UF plans demonstrated substantial reductions in urethra D10 (92.4 Gy) and rectum D2 cm³ (42.7 Gy) compared to WG and hemi plans.
• Focal plans, particularly UF, showed greater sensitivity to seed displacement errors.

Conclusions:

• Focal LDR brachytherapy treatment planning is feasible.
• Focal brachytherapy significantly reduces dose to organs at risk (urethra, rectum).
• Precise seed positioning is critical for ultra-focal treatment plans due to increased sensitivity to displacement.