Isodose patterns in patients with inadequate prostate brachytherapy coverage.

Area of Science:

• Medical Physics
• Radiation Oncology
• Urologic Oncology

Background:

• Developing real-time dosimetry systems is crucial for enhancing prostate brachytherapy outcomes.
• Accurate dose distribution in prostate implants directly correlates with cancer control rates.
• Intraoperative assessment can guide seed placement adjustments for optimal dosimetry.

Purpose of the Study:

• To demonstrate the utility of intraoperative isodose reconstruction for identifying inadequate prostate implants.
• To show that real-time dosimetry can guide corrective seed placement during brachytherapy.
• To validate isodose patterns as predictors of implant quality without precise prostatic volume registration.

Main Methods:

• 102 Pd-103 prostate implants were analyzed using postimplant CT scans.
• Varian Variseed 7.0 software was used for contouring and source entry.
• Dosimetric parameters (V100, D90) and isodose patterns (gaps, holes, islands) were evaluated.

Main Results:

• Isodose holes and islands at midprostate were highly predictive of a V100 < 80% (86% likelihood).
• The presence of midprostatic isodose holes correlated with V100 < 80% in 55% of cases.
• Isodose islands within the prostate were observed in all patients with V100 < 80% when analyzing the entire prostate.

Conclusions:

• Intraoperative isodose pattern analysis provides practical guidelines for postimplant assessment.
• Identifying isodose holes or islands guides the addition of seeds to achieve a V100 > 80%.
• This semiquantitative approach facilitates rational intraoperative modifications for improved implant quality.