Program Information
Establishing MicroCT Imaging Dose to Mouse Organs Using a Validated Monte Carlo Model of the Small Animal Radiation Research Platform
CD Johnstone* and M Bazalova-Carter, University of Victoria, Victoria, BC, Canada
Presentations
SU-E-FS1-4 (Sunday, July 30, 2017) 1:00 PM - 1:55 PM Room: Four Seasons 1
Purpose: Validation of Monte Carlo(MC) model of the Small Animal Radiation Research Platform(SARRP) to determine imaging dose to mouse organs for various imaging protocols, and scatter contributions to half-value-layer(HVL).
Methods: Depth dose and profile measurements using Gafchromic EBT3 film in solid water were conducted at 0-72mm depths at three source-to-surface distances for the 220kVp therapy beam of the SARRP, using 10x10-3x3mm2 square and 1 and 0.5mm diameter circular collimated fields. Dose output measurements at 2cm depth in solid water, and HVL, were obtained for the 220kVp therapy beam and 40-80kVp imaging beams with a Farmer-type ionization chamber. Depth dose curves, dose profiles, and wall-scatter contributions to HVL from the SARRP walls were modeled with EGSnrc MC code. A microCT scan of a mouse was segmented into organs for imaging dose calculations using our SARRP MC model.
Results: The mean and maximum depth dose difference between measurements and MC data was 2.6% and 9.1%, respectively. Dose profiles within penumbra for square fields were within 2.1% with a maximum difference of 7.2%. Absolute dose output differences were 2.2% and 2.9% for the therapy and imaging beams, respectively. Experimental and MC calculated HVL values were within 2% for all energies. Mean organ imaging doses for a typical 60kVp 1-minute scan ranged from 3.5-17.4cGy and 2.6-16.1cGy in the standard and pancake geometries, respectively. Mean body and organ doses were 20% and 8-38% higher, respectively, in the standard geometry compared to pancake geometry. Finally, HVL measurement in the confined SARRP cabinet resulted in less than a 0.5% difference from MC simulations modeling a scatter-free geometry.
Conclusion: Our MC model was validated with measurement and used to determine imaging dose to mouse organs using the SARRP pancake(rotating couch) and standard(rotating source and detector) imaging geometries, as well as determined scatter-free conditions for HVL measurements.
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