Tumor dose specification of I-125 seed implants

Area of Science:

• Medical Physics
• Radiation Oncology
• Brachytherapy

Background:

• Interstitial brachytherapy utilizes radioactive seeds for localized radiation delivery.
• Accurate dosimetry is crucial for effective cancer treatment and minimizing side effects.
• Iodine-125 (I-125) seeds are commonly used in brachytherapy due to their suitable physical characteristics.

Purpose of the Study:

• To present a novel calculation procedure for interstitial implants using I-125 seeds.
• To provide guidance on the total activity of I-125 seeds needed for a minimum dose of 1 Gy based on implant volume and seed spacing.
• To enable clinicians to prescribe specific doses for primary or boost treatments.

Main Methods:

• Development of a new computational method for interstitial implant dosimetry.
• Analysis of dose delivery as a function of implant volume and seed spacing.
• Inclusion of elongation and shape corrections in the calculations.
• Comparison with established dosimetric metrics like matched peripheral dose and average minimum dose.

Main Results:

• The study provides a procedure to determine I-125 seed activity for a target minimum dose (1 Gy).
• Net minimum dose was found to be relatively insensitive to variations in seed spacing for a fixed total activity.
• The net minimum dose also showed insensitivity to individual seed activity variations.

Conclusions:

• The presented calculation procedure facilitates precise dose prescription in I-125 interstitial brachytherapy.
• Clinicians can utilize the provided data to select appropriate I-125 seed activity for various implant volumes.
• The findings support the robustness of I-125 brachytherapy dosimetry against minor variations in seed placement and activity.