# Predictive Factors and Clinical Impact of Radioactive Seed Migration After Prostate Brachytherapy: A Retrospective Study

## TL;DR

This study finds that radioactive seed migration after prostate brachytherapy is common but usually harmless, though significant migration may reduce treatment effectiveness.

## Contribution

The study identifies specific risk factors and clinical implications of seed migration in prostate brachytherapy.

## Key findings

- Seed migration occurred in 24.5% of patients, primarily to the lungs, vasculature, or seminal vesicles.
- Migration of three or more seeds was linked to reduced dose coverage and worse biochemical control trends.
- Larger prostate volume, higher seed count, and more needles increased migration risk, while neoadjuvant hormone therapy reduced it.

## Abstract

We evaluated the frequency and clinical impact of radioactive seed migration after prostate brachytherapy. Among 611 patients, 25% experienced seed migration, most commonly to the lungs, vasculature, or seminal vesicles. Although limited migration did not affect treatment outcomes, the migration of three or more seeds was associated with reduced dose coverage and with a trend toward worse biochemical control. Larger prostate volume, greater number of seeds, and more needles increased the risk of migration. Notably, patients who received neoadjuvant hormone therapy were less likely to experience seed migration. Seed migration is usually not harmful; however, understanding its risk factors is important to improve treatment planning. Using linked seeds and precise techniques may help minimize migration and optimize the effectiveness of brachytherapy in patients with prostate cancer.

Radioactive seed migration after low-dose-rate brachytherapy (LDR-BT) for prostate cancer is a known phenomenon; however, its clinical impact remains unclear. We retrospectively analyzed 611 patients treated with LDR-BT using loose iodine-125 seeds. Post-treatment imaging was used to assess seed migration. Treatment efficacy was evaluated using post-plan dosimetry (V100 and D90) and biochemical recurrence-free survival (bRFS). Seed migration was observed in 150 patients (24.5%) within 1–3 months post-treatment, involving a total of 210 seeds. Migration sites included lungs, vasculature, and seminal vesicles. Hematogenous migration was significantly associated with higher seed counts. Seminal vesicle migration was linked to increased needle usage and absence of neoadjuvant hormone therapy. No significant differences were observed in V100, D90, or bRFS between patients with or without seed migration. However, migration of ≥3 seeds correlated with significantly lower V100 and with a trend toward decreased bRFS. Limited seed migration appears to have minimal clinical impact. However, ≥3 migrated seeds may reduce dosimetric quality and affect treatment efficacy. Risk factors include larger prostate volume as well as higher seed and needle counts. Improved planning and using linked seeds may reduce migration and improve outcomes in LDR-BT for prostate cancer.