Comparison between high and low source activity seeds for I-125 permanent seed prostate brachytherapy

Area of Science:

• Oncology
• Radiation Oncology
• Medical Physics

Background:

• Permanent seed brachytherapy is a common treatment for prostate cancer.
• Iodine-125 (I-125) is a frequently used radioactive isotope for brachytherapy seeds.
• Optimizing seed activity is crucial for balancing treatment efficacy and toxicity.

Purpose of the Study:

• To compare the impact of low versus high Iodine-125 seed activity on seed loss, dosimetric outcomes, and toxicity in prostate cancer brachytherapy.

Main Methods:

• A study of 199 prostate cancer patients undergoing I-125 permanent seed brachytherapy.
• Patients were divided into two cohorts based on seed activity: lower (mean 0.44 mCi) and higher (0.61 mCi).
• Dosimetric parameters (V100, V150, V200, D90), rectal dose (D2), seed loss, and urinary toxicity (IPSS) were assessed post-implantation.

Main Results:

• Lower seed activity correlated with reduced V150 and V200, indicating better dose homogeneity.
• The lower activity group showed a trend towards more patients achieving V100 <90% and D90 <140 Gy.
• No significant difference in rectal dose or overall IPSS scores was observed, though a trend towards increased urinary toxicity with higher activity seeds was noted at 4 and 8 months. Seed loss percentages were comparable between groups.

Conclusions:

• Higher I-125 seed activity (≥ 0.6 mCi) achieves comparable V100 and D90, but may lead to dose inhomogeneity.
• A trend towards increased urinary toxicity at 4 and 8 months suggests potential for higher long-term urinary complications with higher seed activity.