Speakers:
Student presentation: Alex Demelo
Title: Monte Carlo simulations of an electronic portal imaging device (EPID) toward error detection in patient dose delivery
Abstract:
In-vivo dosimetry, the measurement of the dose delivered to the patient during treatment, is an important, and in some countries mandatory, part of external beam radiation therapy treatments (EBRT), as it allows delivery errors to be detected. One method of performing in-vivo dosimetry involves using electronic portal imaging devices (EPIDs) to reconstruct 3D patient dose maps from 2D transmitted field measurements. Given their high spatial resolution, fast collection time, and high signal sensitivity, EPIDs are powerful dosimetry tools. However, the conversion of EPID signal into a clinically meaningful quantity is a non-trivial process and is sensitive to the corrections and calibration factors necessary to relate the measured EPID pixel intensities to dose to water. These uncertainties limit the accuracy of EPID dose reconstructions. A proposed solution for the EPID calibration is to combine a detailed Monte Carlo model of the EPID with film measurements of dose inside the EPID panel assembly. While this approach is not clinically feasible in the long term, it provides the most direct validation of EPID response in the lab setting.
In this presentation, an overview of the methods and challenges of performing EPID dosimetry measurements for EBRT will be given. The newly proposed film-based calibration methodology will be described. Preliminary work towards refining this methodology and understanding its applications and limits will be presented.
Member presentation: Richard B. Richardsona,b
aRadiobiology and Health Branch, Chalk River Laboratories, Canadian Nuclear Laboratories, Chalk River, ON, K0J 1J0, Canada.
bMcGill Medical Physics Unit, Cedars Cancer Centre-Glen Site, Montreal, QC, H4A 3J1, Canada.
Title: The Interconnectedness of Oxygen Levels, Inflammation, Other Mediators and Radiation-Induced Cataracts in Astronauts and A-Bomb Survivors
Abstract:
This presentation will first describe cataract development and the main three age-related cataract types. Canada’s expanding role in space exploration will then be outlined and the high radiation doses expected in future missions to the Moon and Mars. Spacecraft atmospheres before 1976 promoted a different cataract type in NASA astronauts to those observed in astronauts on later missions. The reason for this, I postulated in a peer-reviewed publication in 2022, was due to the lens of the eye requiring an optimal ‘Goldilocks’ range of oxygen levels and the radiation oxygen effect. Like astronauts, A‑bomb survivors have significantly higher dose‑related risks of cataracts and other eye disorders; however, both cohorts also exhibit several cataractogenic mediators intermediate risk factors or mediators such as inflammation. A Monte Carlo, Multi-Tissue Eye model was developed to assess the cataract risk to the irradiated lens and non-lens ocular targets of inflammation from electrons, photons, and neutrons. Consequently, by accounting for mediators and non-lens targets, the impact of ionizing radiation on vision impairment may currently be underestimated for Moon and Mars missions — and diagnostic imaging and radiotherapy procedures.