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Dosimetric Characterization of a Low Energy Directional LDR Brachytherapy Source

I Veltchev*, X Chen , R Price , C Ma , Fox Chase Cancer Center, Philadelphia, PA


(Monday, 7/15/2019) 1:15 PM - 1:45 PM

Room: Exhibit Hall | Forum 6

Purpose: The directional planar LDR device, CivaSheet, is an array of directionally shielded palladium-103 sources (CivaDots). The presence of high gradients in the dose distribution around the shielded CivaDot necessitates accurate tabulation of the dosimetric quantities in order to be used in a modified TG-43 formalism.

Methods: A FLUKA Monte Carlo simulation of a single CivaDot source was designed. The FLUKA transport code has been previously successfully used in various medical applications, including characterization of brachytherapy sources. In order to benefit from the symmetry of the CivaDot design, cylindrical scoring geometry was utilized to obtain faster tallying convergence at large distances from the source. The tabulated quantities include radial dose function analog, 2D anisotropy function analog, and dose-rate constant. A point source geometry function was used. The obtained results were benchmarked against recently published MCNP6 data and EBT3 film measurements.

Results: The radial dose function analog was calculated for radial distances up to 5 cm and the values were found to be within one standard deviation from the EBT3 film measurements; a more accurate result than previously obtained with MCNP6. For all polar angles and radial distances not exceeding 4 cm, the computed 2D anisotropy function differed from the values obtained from film by no more than 10%. Dose-rate constant of 0.587(19) cGy/h/U was calculated from the dose rate in water at radial distance of 1 cm and the air-kerma strength as calculated in a separate in vacuo simulation using FLUKA. This value differs by only 1.4% from the previously reported value obtained using MCNP6.

Conclusion: The complex dose distribution around the directionally shielded CivaDot LDR source was successfully quantified in terms of TG-43 parameters derived from a Monte Carlo simulation using FLUKA. The obtained results show better agreement with film measurements than MCNP6.


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