Monte Carlo dosimetry of the VariSource high dose rate 192Ir source

Area of Science:

• Medical Physics
• Radiotherapy Dosimetry
• Nuclear Medicine

Background:

• Accurate dosimetry data is crucial for effective brachytherapy.
• High dose rate (HDR) Iridium-192 (192Ir) sources are widely used in interstitial brachytherapy.
• Standardized dosimetry formalisms, such as AAPM Task Group 43, are essential for consistent dose calculations.

Purpose of the Study:

• To compute fundamental dosimetry parameters for the VariSource HDR 192Ir source in water.
• To provide data for dose calculation in accordance with established brachytherapy formalisms.
• To establish a reliable dataset for clinical application and further research.

Main Methods:

• Utilized a modified EGS4 Monte Carlo code for precise dose distribution calculations.
• Simulated transverse-axis and two-dimensional dose distributions.
• Calculated air-kerma strength and derived key dosimetry data including dose rate constant, radial dose function, and anisotropy function.

Main Results:

• The calculated dose rate constant is 1.044 ± 0.2% cGy h⁻¹ per unit air-kerma strength.
• The anisotropy function showed significant deviations (40%-60%) from isotropy along the source's long axis.
• The radial dose function closely matched that of the microSelectron HDR 192Ir source, with minor differences (<2.8%) at distances <0.5 cm.

Conclusions:

• The generated dosimetry data provides essential information for the VariSource HDR 192Ir source.
• The data supports accurate dose calculations in clinical brachytherapy settings.
• Comparison with other 192Ir sources and fitting formulas validates the Monte Carlo results.