Correction factors for source strength determination in HDR brachytherapy using the in-phantom method.

Area of Science:

• Medical Physics
• Radiotherapy Physics
• Dosimetry

Background:

• Accurate clinical source strength determination is crucial for High Dose Rate (HDR) brachytherapy.
• The German Society for Medical Physics (DGMP) recommends specific phantoms and chambers for calibration.
• Existing calibration methods may have systematic deviations requiring further investigation.

Purpose of the Study:

• To model the calibration chain for HDR brachytherapy sources using Monte Carlo simulations.
• To determine global correction factors (k(tot)) for converting ionization chamber readings to Ka,100 and Dw,1.
• To compare Monte Carlo-derived factors with existing recommendations and experimental measurements.

Main Methods:

• Monte Carlo simulations were employed to model the calibration process in a solid-state phantom (Krieger-phantom).
• Global correction factors were calculated for various Ir-192 and Co-60 HDR sources using different thimble ionization chambers.
• Experimental measurements were performed on μSelectron V2 HDR sources to validate the simulation results.

Main Results:

• Monte Carlo-derived correction factors showed systematic differences (2-2.5%) compared to DGMP 13 data.
• Experimental results using direct Ka,100 calibration were systematically lower by approximately 1.5%.
• Monte Carlo-based factors provided the smallest deviation from manufacturer certificates for μSelectron V2 sources.

Conclusions:

• Monte Carlo simulations offer a robust method for determining global correction factors in HDR brachytherapy dosimetry.
• The calculated correction factors enable accurate determination of Ka,100 for HDR Co-60 sources via in-phantom measurements.
• The presented factors facilitate the determination of Dw,1 using the same in-phantom setup, enhancing clinical applicability.