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SU‐G‐201‐06: Directional Low‐Dose Rate Brachytherapy: Determination of the TG‐43 Dose‐Rate Constant Analog for a New Pd‐103 Source
Author(s) -
Aima M,
Culberson W,
Hammer C,
Micka J,
DeWerd L
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4956879
Subject(s) - monte carlo method , dosimetry , imaging phantom , brachytherapy , dosimeter , thermoluminescent dosimeter , materials science , kerma , ionization chamber , nuclear medicine , optics , physics , mathematics , radiation therapy , medicine , ionization , statistics , ion , quantum mechanics
Purpose: The aim of this work is to determine the TG‐43 dose‐rate constant analog for a new directional low‐dose rate brachytherapy source based on experimental methods and comparison to Monte Carlo simulations. The CivaSheet™ is a new commercially available planar source array comprised of a variable number of discrete directional source elements called “CivaDots”. Given the directional nature and non‐conventional design of the source, modifications to the AAPM TG‐43 protocol for dosimetry are required. As a result, various parameters of the TG‐43 dosimetric formalism have to be adapted to accommodate this source. This work focuses on the dose‐rate constant analog determination for a CivaDot. Methods: Dose to water measurements of the CivaDot were performed in a polymethyl methacrylate phantom (20×20×12 cm 3 ) using thermoluminescent dosimeters (TLDs) and Gafchromic EBT3 film. The source was placed in the center of the phantom, and nine TLD micro‐cubes were irradiated along its central axis at a distance of 1 cm. For the film measurements, the TLDs were substituted by a (3×3) cm 2 EBT3 film. Primary air‐kerma strength measurements of the source were performed using a variable‐aperture free‐air chamber. Finally, the source was modeled using the Monte Carlo N‐Particle Transport Code 6. Results: Dose‐rate constant analog observed for a total of eight CivaDots using TLDs and five CivaDots using EBT3 film was within ±7.0% and ±2.9% of the Monte Carlo predicted value respectively. The average difference observed was −4.8% and −0.1% with a standard deviation of 1.7% and 2.1% for the TLD and the film measurements respectively, which are both within the comparison uncertainty. Conclusion: A preliminary investigation to determine the doserate constant analog for a CivaDot was conducted successfully with good agreement between experimental and Monte Carlo based methods. This work will aid in the eventual realization of a clinically‐viable dosimetric framework for the CivaSheet. This work was partially supported by NCI contract (HHSN261201200052C) through CivaTech Oncology Inc.