Variability of prostate brachytherapy pre-implant dosimetry: a multi-institutional analysis

Area of Science:

• Radiation Oncology
• Medical Physics
• Urologic Oncology

Background:

• Prostate brachytherapy is a common treatment for localized prostate cancer.
• Pre-implant dosimetry is critical for optimizing radiation dose distribution.
• Multi-institutional studies require standardized dosimetry for reliable comparisons.

Purpose of the Study:

• To compare pre-implant dosimetry for palladium-103 (Pd-103) and iodine-125 (I-125) prostate brachytherapy across multiple institutions.
• To identify and quantify variability in dosimetry parameters.
• To assess the impact of variability on treatment planning.

Main Methods:

• Eight experienced brachytherapists submitted Pd-103 and I-125 dosimetry plans.
• All plans were based on the same transrectal ultrasound volumetric data.
• Dosimetric analysis included target volume, seed characteristics, dose coverage (V100, V150, V200), dose metrics (D90, D50), urethral dosimetry, and treatment margins.

Main Results:

• Significant variability observed in planning target volume, treatment margins, and extracapsular seed placement.
• While prostate coverage (V100 >95%) was consistent, dose homogeneity (V150, V200) varied widely.
• Urethral dosimetry showed considerable variation in median dose, despite consistent V100.

Conclusions:

• Substantial variability exists in prostate brachytherapy pre-implant dosimetry parameters, including target volume, dose homogeneity, margins, and seed placement.
• Despite uniform prescription doses, these variations hinder meaningful multi-institutional comparisons of outcomes.
• Standardization of pre-implant dosimetry is essential for improving the reliability and comparability of prostate brachytherapy research.