SU‐F‐19A‐05: Experimental and Monte Carlo Characterization of the 1 Cm CivaString 103Pd Brachytherapy Source

Abstract

Purpose:To determine the in‐air azimuthal anisotropy and in‐water dose distribution for the 1 cm length of the CivaString 103Pd brachytherapy source through measurements and Monte Carlo (MC) simulations. American Association of Physicists in Medicine Task Group No. 43 (TG‐43) dosimetry parameters were also determined for this source.Methods:The in‐air azimuthal anisotropy of the source was measured with a NaI scintillation detector and simulated with the MCNP5 radiation transport code. Measured and simulated results were normalized to their respective mean values and compared. The TG‐43 dose‐rate constant, line‐source radial dose function, and 2D anisotropy function for this source were determined from LiF:Mg,Ti thermoluminescent dosimeter (TLD) measurements and MC simulations. The impact of 103Pd well‐loading variability on the in‐water dose distribution was investigated using MC simulations by comparing the dose distribution for a source model with four wells of equal strength to that for a source model with strengths increased by 1% for two of the four wells.Results:NaI scintillation detector measurements and MC simulations of the in‐air azimuthal anisotropy showed that ≥95% of the normalized data were within 1.2% of the mean value. TLD measurements and MC simulations of the TG‐43 dose‐rate constant, line‐source radial dose function, and 2D anisotropy function agreed to within the experimental TLD uncertainties (k=2). MC simulations showed that a 1% variability in 103Pd well‐loading resulted in changes of <0.1%, <0.1%, and <0.3% in the TG‐43 dose‐rate constant, radial dose distribution, and polar dose distribution, respectively.Conclusion:The CivaString source has a high degree of azimuthal symmetry as indicated by the NaI scintillation detector measurements and MC simulations of the in‐air azimuthal anisotropy. TG‐43 dosimetry parameters for this source were determined from TLD measurements and MC simulations. 103Pd well‐loading variability results in minimal variations in the in‐water dose distribution according to MC simulations.This work was partially supported by CivaTech Oncology, Inc. through an educational grant for Joshua Reed, John Micka, Wesley Culberson, and Larry DeWerd and through research support for Mark Rivard.