Good morning,
I'm running an OpenTopas (v 4.0) simulation for a carbon ion source (250 MeV/u) on a water phantom using the RBE_TabulatedAlphaBeta scorer, not referencing any subscorer for physical dose.
Me and @wahln noticed underestimated values for the output LQ parameters. Upon closer look, the culprit seems to be the handling of secondary electrons and photons. Specifically, the subscorer TsScoreDoseAlpha_Tabulated filters out these secondaries (they have zero atomic number) so that their contribution to the "alphaDose" (at numerator) is disregarded. However, the default DoseToWater scorer (at denominator) used for averaging still accounts for the dose deposited by such secondaries, thus underestimating the LQ parameters.
The effect is clear when a dummy alpha table is used, with all alpha values set to unity for any energy and fragment. The dose averaged prediction should be a constant profile at 1 /Gy, but the obtained profile (black) is up to 10% lower at entrance.
The amount of long range secondary electrons produced decreases approaching the beam range and the profile gets closer to the expected unity. As a double check, the profile gets close to one once the cut for electrons is set to very high values and all electrons are deposited locally (red profile).
As a proposed fix, we implemented a small correction to return the reference alphaX and betaX values for the cell line when the particle atomic number is zero or not available in the input alpha/beta table.
I'll be happy to further discuss this aspect and contribute to the implementation of a permanent solution.
Thank you for your help,
Best
Remo
Good morning,
I'm running an OpenTopas (v 4.0) simulation for a carbon ion source (250 MeV/u) on a water phantom using the
RBE_TabulatedAlphaBetascorer, not referencing any subscorer for physical dose.Me and @wahln noticed underestimated values for the output LQ parameters. Upon closer look, the culprit seems to be the handling of secondary electrons and photons. Specifically, the subscorer
TsScoreDoseAlpha_Tabulatedfilters out these secondaries (they have zero atomic number) so that their contribution to the "alphaDose" (at numerator) is disregarded. However, the defaultDoseToWaterscorer (at denominator) used for averaging still accounts for the dose deposited by such secondaries, thus underestimating the LQ parameters.The effect is clear when a dummy alpha table is used, with all alpha values set to unity for any energy and fragment. The dose averaged prediction should be a constant profile at 1 /Gy, but the obtained profile (black) is up to 10% lower at entrance.
The amount of long range secondary electrons produced decreases approaching the beam range and the profile gets closer to the expected unity. As a double check, the profile gets close to one once the cut for electrons is set to very high values and all electrons are deposited locally (red profile).
As a proposed fix, we implemented a small correction to return the reference
alphaXandbetaXvalues for the cell line when the particle atomic number is zero or not available in the input alpha/beta table.I'll be happy to further discuss this aspect and contribute to the implementation of a permanent solution.
Thank you for your help,
Best
Remo