Speakers
Dinindu Gunasekara (Carleton University)
“Simulating Biodosimetry Calibration Curves through Monte Carlo Modelling of Chromosome Aberrations”
Biodosimetry is an important tool for assessing the amount of radiation absorbed by an individual. In contrast to physical dosimetry, which can provide information about the quantity of radiation, biodosimetry is capable of accounting for biological factors present during irradiation. Biodosimetry techniques employ a dose calibration curve to convert biological damage induced by ionizing radiation to an amount of dose received. At Health Canada, these curves are produced with X-rays which may not match the quality of the radiation involved in an exposure scenario such as the mixed radiation fields as found on the International Space Station. Using a computational model, the impact of using a more realistic source of radiation for calibration curves can be assessed.
The objective my work is to model the chromosome aberrations resulting from X-ray irradiation and simulate a calibration curve as a starting point towards this goal. This was accomplished using a validated fibroblast cell model and an associated DNA damage-scoring algorithm in TOPAS-nBio, the yield of DNA double strand breaks caused by 250 kV X-ray irradiation was simulated. This distribution of damage was output in the Standard for DNA Damage (SDD) format, and used as an input for the Mechanistic DNA Repair and Survival (MEDRAS) model. Various endpoints were simulated including dicentric chromosomes and translocations at a range of dose points up to 2 Gy to produce a calibration curve. This curve was compared to laboratory results for dicentrics and translocations to validate the model. During the comparison process, a fair amount of interlaboratory variation was found. Current work involves investigating adjusting the parameters in the MEDRAS model to better match a chosen laboratory’s data. Comparison of current simulation results to available laboratory data will be presented.
Ernesto Mainegra-Hing (NRC)
“Monte Carlo in x-ray dosimetry standards”
Dosimetry standards for kilovoltage x-rays have been in operation at the NRC for more than 60 years. The main development of the instrumentation and procedures occurred before the adoption of computers in science, and therefore analytical and experimental procedures have become embedded in the determination of the primary quantity of interest, air kerma, for example in the determination of attenuation coefficients and correction factors.
However, in parallel with the development of measurement standards, NRC has been a leader in the use of computer simulations for ionizing radiation applications, to complement experimental/analytical techniques, and in some cases, replace them. This presentation will explore the role of Monte Carlo radiation transport systems, and particularly EGSnrc, in improving and expanding the kV x-ray standards maintained at NRC, and their dissemination to Canadian users through calibration services.