Two-dimensional dose distribution around a commercial 125I seed

Area of Science:

• Medical Physics
• Radiation Oncology
• Nuclear Medicine

Background:

• Brachytherapy utilizes sealed radioactive sources for localized radiation treatment.
• Iodine-125 (125I) seeds are commonly used in brachytherapy due to their favorable dosimetry characteristics.
• Accurate dose distribution data is crucial for effective treatment planning and minimizing off-target radiation exposure.

Purpose of the Study:

• To investigate the dose distribution of the 3M Company model 6711 125I seed.
• To compare the dose distribution of the 6711 seed with the 3M Company model 6702 125I seed.
• To assess the impact of manufacturing variations, specifically end-weld thickness, on the dose distribution of the 6711 seed.

Main Methods:

• The Monte Carlo method was employed for simulating radiation transport.
• Dose rate per unit activity data were calculated at 63 points around the 125I seed in a water phantom.
• Relative dose distributions were generated and compared graphically between the 6711 and 6702 seeds.

Main Results:

• The 3M 6711 125I seed exhibits a dose distribution that falls off more rapidly with distance compared to the 3M 6702 125I seed.
• Graphical analysis confirmed differences in radial dose profiles between the two seed models.
• Variations in end-weld thickness of the 6711 seed were found to introduce substantial uncertainties in dose distribution at specific locations.

Conclusions:

• The 3M 6711 125I seed has a distinct dose profile compared to the 6702 seed, characterized by faster dose fall-off.
• Manufacturing variations, particularly end-weld thickness, significantly impact the dosimetric accuracy of the 6711 seed.
• These findings highlight the importance of considering seed model specific dosimetry and manufacturing tolerances in brachytherapy treatment planning.