Help with F4 Fm4 dose calculation in MCNP simulation

[alinegranja]

TL;DR Summary

Struggling with dose calculation in MCNP for brachytherapy using Ho-166. Using Fm -1 0 -5 -6 for photons results in zero, unlike F6/F8. Need help configuring F4:e,p with Fm4 to accurately calculate deposited dose for both photons and electrons.

Hello everyone,

I am facing difficulties while trying to calculate the dose in the tibia due to brachytherapy in an MCNP simulation. We are working with the radionuclide Ho-166, and therefore, we need to account for both photon and electron contributions to the deposited dose.

Initially, I used the card Fm -1 0 -5 -6 for photons, but the result was zero, compared to the results obtained with the F6 and F8 cards. I would like to better understand the correct way to configure the dose calculation in the region of interest (tibia). Additionally, I have not found a clear reference for how to use the F4(FMESH4) card with the :e,p specification to properly calculate the dose with the Fm4 card.

Could someone help me understand the correct configuration to obtain the expected results for deposited dose in MCNP, considering both photon and electron contributions?

Thank you in advance for your help!

 

[Alex A]

Welcome to Physics Forums @alinegranja,

It is my current understanding that...

If the target is not modeled in the input file, DE/DF cards can be used to get the expected dose from the flux. Prior to 6.3 there are even built in functions. This would be expected full body dose and not what you want I think, but it might be worth double checking the answers with these numbers. They should be close.

If the target is present and accurately modeled (the shape need not be exact), the density is right, the total masses are right then an F6 tally would report how much energy is deposited in the cell. Using *F6 would give the answer in jerks per gram (per source particle), multiplying that by 10^12 should then give you Joules per kg (per source particle). Taking that value and multiplying by the activity and the exposure length should then give a dose in Grays.

The FM card is usually used to multiply the flux in a tally by a cross section and integrate, for example to find the rate a reaction happens. I don't understand why it would be used here.

I hope this helps, and best of luck working it all out!