Pre-plan parameters predict post-implant D90 ≥ 140 Gy for (125)I permanent prostate implants

Area of Science:

• Radiation Oncology
• Medical Physics
• Urologic Oncology

Background:

• Permanent prostate implant (PPI) brachytherapy is a treatment for low or intermediate-risk prostate cancer.
• Achieving adequate radiation dose (D90) is critical for treatment efficacy.
• Predictive dosimetric parameters from pre-treatment planning are needed to optimize outcomes.

Purpose of the Study:

• To identify pre-plan dosimetric parameters that predict a post-implant D90 of ≥ 140 Gy.
• To improve the precision of permanent prostate implant (PPI) planning.

Main Methods:

• Analysis of pre-plans for 504 patients undergoing (125)I PPI.
• Evaluation of seed numbers, occupancy proportions, and margin distances across various prostate segments.
• Correlation of pre-plan parameters with post-implant D90 (≥ 140 Gy vs. < 140 Gy).

Main Results:

• 20% of patients had a post-implant D90 < 140 Gy.
• Higher anterior D90 (AT, IA) seed counts and larger anterior/mid-gland margins (WP, S, A, SA, ST, AT, MT) were associated with D90 ≥ 140 Gy.
• Reduced posterior segment (PT) occupancy proportion and smaller posterior margins (P) were also noted in the higher D90 group.

Conclusions:

• Pre-plan parameters, specifically anteriorly placed seeds and larger margins, are predictive of achieving a D90 ≥ 140 Gy.
• Posteriorly reduced seed occupancy and smaller margins also predict successful dose delivery.
• Optimizing these pre-plan dosimetric factors can enhance permanent prostate implant (PPI) outcomes.