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A Public Collection of Reference Dosimetry Ionization Chamber Models in EGSnrc

R Townson1*, J Lad2, F Tessier1, (1) National Research Council Canada, Ottawa, ON, CA, (2) McMaster University, Hamilton, ON, CA


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library


International protocols for radiation dosimetry rely on detailed Monte Carlo simulations of individual electrons and photons interacting within ionization chambers. Technical chamber specifications are proprietary, and thus cannot be shared with collaborators nor peer reviewed. To alleviate this issue, a collection of ionization chamber models has been developed and will be publicly distributed with EGSnrc. There are three immediate benefits: 1) users can model detectors quickly, without building geometries from scratch; 2) simulation results can be compared and peer-reviewed; 3) models are continuously validated by a community of users.


Three out of the five leading companies we contacted decided to participate at this initial stage: Standard Imaging (US), PTW (Germany) and Pheonix Dosimetry (UK). We worked with each company to determine the design elements that could be disclosed publicly, within EGSnrc plain text input files. Each manufacturer allowed us to reach an agreeable level of detail deemed suitable for public release, yet also sufficient for accurate simulation. Twelve chamber models were developed.


All of the chamber models were validated with using the Fano test. Dose to the chamber cavity was calculated for each chamber using the egs_chamber application. To illustrate the effect that the chamber geometry and materials have on the dose, each was compared to the Pheonix Dosimetry NE2571 chamber. Doses to the other chambers differed by as much as 1% in a 1.25 MeV photon beam, using otherwise identical simulation parameters.


Accurate EGSnrc simulation models for 12 ionization chambers were built to be released publicly. We trust that this initial effort will prompt other vendors to disclose data for their detectors, and inspire developers of other Monte Carlo packages to contribute equivalent models.


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