Paul Prior and Lindsay Beaton

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Thursday, April 17, 2014
Conference room A&B, Room C2363, 2nd floor, Cancer Centre South, The Ottawa Hospital - General Campus, 501 Smyth Road

1. "An iterative triple energy window approach for cross talk correction in dual isotope Tc99m & In111 small animal SPECT"
Paul Prior - Carleton University

Abstract: Dual isotope SPECT allows simultaneous measurement of two different tracers in vivo. With In111 (emission energies of 171keV and 245keV) and Tc99m (140keV), quantification of Tc99m is degraded by cross talk from the In111 photons that scatter and are detected at an energy corresponding to Tc99m. The Triple Energy Window (TEW) uses counts recorded in two narrow windows surrounding the Tc99m primary window to estimate scatter. Iterative TEW corrects for the bias introduced into the TEW estimate resulting from un-scattered counts detected in the scatter windows. The contamination in the scatter windows is iteratively estimated and subtracted as a fraction of the scatter-corrected primary window counts. The iterative TEW approach was validated with a small-animal SPECT/CT camera using a 2.5mL plastic container holding thoroughly mixed Tc99m/In111 activity fractions of 0.15, 0.28, 0.52, 0.99, 2.47 and 6.90.  Dose calibrator measurements were the gold standard. Uncorrected for scatter, the Tc99m activity was over-estimated by as much as 80%. Unmodified TEW underestimated the Tc99m activity by 13%.  With iterative TEW corrections applied in projection space, the Tc99m activity was estimated within 5% of truth across all activity fractions above 0.15. This is an improvement over the non-iterative TEW, which could not sufficiently correct for scatter in the 0.15 and 0.28 phantoms.

2. "Astronaut Biodosimetry"
Lindsay Beaton - Health Canada

Abstract: Radiation induces damage to DNA which can be measured using cytogenetic endpoints to determine the level of exposure of an individual based on biological markers.  This method is termed biodosimetry and is essential for triage in the case of a large scale radiological/nuclear emergency.  Cytogenetic endpoints are also routinely used in other research projects, such as the identification of individual radiation sensitivity biomarkers, as well as the cytogenetic analysis of blood samples from astronauts. The biodosimetry of these astronaut samples provides an in vivo measurement of the biological damage from space radiation. This talk will focus on the biodosimetry methods used by Health Canada with a focus on the analysis of Canadian and European astronaut lymphocytes prior to- and post-flight, and will include some of our recent results.