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Dosimetric Characteristics of the CivaDot™ Unidirectional Pd-103 Brachytherapy Source

H Zhen

H Zhen*, G Redler , Y Liao , A Templeton , J Turian , Rush University Medical Center, Chicago, IL


WE-AB-605-7 (Wednesday, August 2, 2017) 7:30 AM - 9:30 AM Room: 605

Purpose: To verify the dosimetric characteristics of a Pd-103 brachytherapy source (CivaDot) using Monte Carlo simulations and Gafchromic EBT3 film dosimetry.

Methods: The CivaSheet (CivaTech, Durham NC) consists of an array of disk-shaped Pd-103 sources, called “CivaDots”, embedded in a bio-absorbable membrane. Each CivaDot is attached to a gold shielding plate, making the source unidirectional. To verify the dosimetric characteristics of the CivaDot, Monte Carlo simulations were performed both in vacuo and in water to obtain the dose rate constant Λ_MC, radial dose function g(r)_MC and 2D anisotropy function F(r,θ)_MC. Experimentally, a specially-designed solid water phantom with an indent that holds a single CivaDot was used to measure the 2D dose distribution with an EBT3 film placed along the CAX direction. Calibration of the EBT3 film was done using a calibrated 50kVp x-ray beam. g(r)_film and F(0.5cm,θ)_film were extracted from the film measurement.

Results: Λ_MC was 0.1% different from Λ_vendor. g(r)_MC is on average -2.1%[-3.3%, 0%] from g(r)_vendor for r between 0.5cm to 5cm. F(0.5cm,θ)_MC is on average within -1.0%[-1.9%,2.3%] from F(0.5cm,θ)_vendor for r between 0.5cm and 5cm, and θ between 0° and 90°. For film measurements, g(r)_film was on average -7.3% [-13.8%, 0.4%] different from g(r)_vendor, for r between 0.3cm and 1.5cm, and F(5mm,θ)_film was on average -1.3% [-5.0%, 2.1%] different from F(5mm,θ)_vendor for θ between 0° and 70°. The difference between film measured and vendor provided values rises to more than 30% with r<0.3cm and θ >70° (i.e. near the edge of the film).

Conclusion: With an independent Monte Carlo simulation, we have successfully verified Λ, g(r), and F(r,θ) of the CivaDot unidirectional Pd-103 source to be within 3.3% from vendor provided values over the clinically useful range. We also demonstrated the potential of using EBT3 films to verify these dosimetric parameters with limited accuracy.

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