Program Information
Cavity Theory Applications for Kilovoltage Cellular Dosimetry
P Oliver*, R Thomson , Carleton Univ, Ottawa, ON
Presentations
SU-F-108-3 (Sunday, July 30, 2017) 2:05 PM - 3:00 PM Room: 108
Purpose: To investigate the relationships between macroscopic (bulk tissue) and microscopic (cellular) dose descriptors for 20 to 370 keV incident photons. Cavity theory predictions are compared with the results of Monte Carlo (MC) simulations involving detailed, multicellular models of human soft tissues.
Methods: Small, large, and multiple intermediate cavity theory (SCT, LCT, and ICT, respectively) approaches are considered; ICT is a sum of SCT and LCT contributions weighted by parameter d. The cavity theory approach having the best overall agreement with MC results is determined via comparison of Dw,m/Dm,m values (where Dw,m is dose-to-water-in-medium and Dm,m is dose-to-medium-in-medium, considering μm-sized cavities). This approach is then used to estimate cell nucleus doses, Dnuc, comparing with results from MC simulations involving multicellular soft tissue models for a range of cell/nucleus sizes and elemental compositions.
Results: The best agreement (minimum root mean square error) with MC results for Dw,m/Dm,m is achieved with an ICT approach in which d=(1–exp(–βL))/(βL), where L is the cavity’s mean chord length and β is given by exp(-β*RCSDA)=0.04 (RCSDA is the continuous slowing down approximation range of an electron of energy equal to that of incident photons). In 91% of cases, ICT and MC predictions of Dnuc/Dm,m agree within 3%; disagreement is at most 8.8%. If MC simulations model only a single nuclear cavity in an otherwise homogeneous bulk tissue phantom instead of multicellular tissue structure, agreement improves to within 6.5%; cavity theory does not account for heterogeneities in cavity surroundings, hence the smaller discrepancy in the simplified case.
Conclusion: This work suggests that cavity theory is useful for linking doses from model-based dose calculation algorithms with energy deposition in cellular targets. Sensitivity of results with respect to the microscopic tissue structure demonstrates the importance of accurate knowledge of cellular compartment sizes and elemental compositions.
Funding Support, Disclosures, and Conflict of Interest: The authors would like to thank the Natural Science and Engineering Research Council of Canada (NSERC), the Canada Research Chairs (CRC) Program, and the Ontario Graduate Scholarship (OGS) for providing funding. Compute Canada and the Shared Hierarchical Academic Research Computing Network (SHARCNET) provided computing resources.
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