Abstract
PurposeThis study aimed to present guidance on the correlation between treatment nozzle and proton source parameters, and dose distribution of a passive double scattering compact proton therapy unit, known as Mevion S250.MethodsAll 24 beam options 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. Track‐averaged LET (LETt) and dose‐averaged LET (LETd) distributions were also calculated. For the sensitivity investigations, proton beam line parameters including Average Energy (AE), Energy Spread (ES), Spot Size (SS), Beam Angle (BA), Beam Offset (OA), and Second scatter Offset (SO) from central Axis, and also First Scatter (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.ResultsFor the physical dose distribution, the MCNPX MC model matched measurements data for all the options to within 2 mm and 2% criterion. The Mevion S250 was found to have a LETt between 0.46 and 8.76 keV.μm–1 and a corresponding LETd between 0.84 and 15.91 keV.μm–1. For all the options, the AE and ES had the greatest effect on the resulting depth of pristine peak and peak‐to‐plateau ratio respectively. BA, OA, and SO significantly decreased the flatness and symmetry of the profiles. The LETs were found to be sensitive to the AE, ES, and SS, especially in the peak region.ConclusionsThis study revealed the importance of considering detailed beam parameters, and identifying those that resulted in large effects on the physical dose distribution and LETs for a compact proton therapy machine.
Highlights
Proton therapy using compact passively scattered systems is undergoing a technological evolution as it eliminates the requirement for a complex beam transport system.[1]
With the number of simulated histories used, the uncertainty associated with statistical uncertainty in the Monte Carlo (MC)‐calculated results in air was less than 0.50% at all distances in the transverse plane
High precision was obtained in the results of the simulations, which was due to simulating large numbers of histories
Summary
Proton therapy using compact passively scattered systems is undergoing a technological evolution as it eliminates the requirement for a complex beam transport system.[1] additional absorbers are added to the gantry due to the lack of an energy selection system in a relatively short beamline. These absorbers significantly complicate the modeling of the system and justify careful characterization with precise and accurate methods to identify beam parameters, i.e. proton source that affect the uncertainty of calculated proton dose distributions.[2]. It is important to provide accurate proton LET distributions with rigorous sensitivity analysis, in addition to the physical dose, for clinical applications
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