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Dosimetric Measurements and Characterization of a New Directional Pd-103 Low-Dose Rate Brachytherapy Source

M Aima

M Aima*, L DeWerd, W Culberson, Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI


SU-H4-GePD-T-4 (Sunday, July 30, 2017) 4:30 PM - 5:00 PM Room: Therapy ePoster Lounge

Purpose: This work focuses on conducting a thorough investigation to ascertain the dosimetric characteristics of a CivaDot prior to its clinical implementation. Various guidelines and dosimetric formalisms have been recommended by the AAPM for conventional LDR sources. The use of these protocols for planar or directional LDR sources such as the CivaDot is precluded as the source geometry and design vary significantly from conventional LDR sources. The primary aim of this work is to characterize the CivaDot dose distribution by performing in-phantom measurements, and Monte Carlo (MC) simulations.

Methods: A PMMA phantom (20×20×12 cm³) was fabricated to perform CivaDot dose-to-water measurements using Gafchromic EBT3 film. The source was placed in the center of the phantom, and six EBT3 films (12×12 cm²) were irradiated simultaneously along its central axis at various depths and read out using a flatbed scanner. CivaDot air-kerma strength was determined using a free-air chamber. A calibration curve was determined by irradiating additional films with sixty-two different dose-to-water levels using a NIST-matched M40 x-ray beam. The source and the phantom setup were modeled using MCNP6.

Results: The CivaDot dose-to-water distribution measured in phantom was compared to the corresponding MC predictions at the six depths. The observed difference using a pixel-by-pixel subtraction map of the measured and the predicted dose-to-water distribution were generally within 2-3%, with maximum differences up to 5%. Analogous TG-43 parameters adapted for a directional source were determined for the CivaDot based on the film measurements, and MC simulations.

Conclusion: Dose distribution measurements of the CivaDot using the EBT3 film stack phantom, and its subsequent comparison to Monte Carlo predicted dose distributions were encouraging, given the overall uncertainties. This work will aid in the eventual realization of a clinically viable dosimetric framework for the CivaSheet and test the feasibility of using an adapted TG-43 dosimetric formalism.

Funding Support, Disclosures, and Conflict of Interest: This work was partially supported by NCI contract (HHSN261201200052C) through CivaTech Oncology Inc.

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