Room: ePoster Forums
Purpose: To present a detailed Monte Carlo (MC) simulation and model sensitivity analysis of a passive double scattering compact proton therapy unit, known as Mevion S250.
Methods: All 24 beam configurations were modeled using the MCNPX MC code. The calculated physical dose for pristine peak, profiles, and spread out Bragg peak (SOBP) were benchmarked with the measured data. Then, for all the configurations, both track-averaged LET (LETt) and dose-averaged LET (LETd) distributions were calculated. For the sensitivity investigations, proton source parameters including Average Energy (AE), Energy Spread (ES), Spot Size (SS), Beam Angle (BA) and Offset from central Axis (OA) and also First Scatterer (FS) thickness were simulated in different stages to obtain the uncertainty of the derived results on the physical dose and LET distribution in a water phantom.
Results: For the physical dose distribution, the MCNPX MC model matched measurements data for all the options to within 2% or 2 mm. The Mevion S250 was found to have a LETt between 0.46 and 8.76 keV.Î¼mâ€“1 and a corresponding LETd between 0.84 and 15.91 keV.Î¼mâ€“1. The proton source parameters having the greatest effect on the resulting dose distributions were AE and BA, as high as 4% for a 0.5Â° deflection. The SS and ES were found to have a smaller impact. Variations in FS thickness were found to have a significant effect on pristine peak (depth of 90% dose). Small OA (>2 mm) of the source caused significant variation to the profiles. The LETs were sensitive to the affecting parameters on the resulting dose distributions.
Conclusion: In this work, distribution maps of the LETt and LETd of a tuned Mevion S250 MC model are presented for LET dose painting. Moreover, the tabulated results of sensitivity analysis can be a useful tool when commissioning and quality assurance of this system.