I need to know an idea to calculate the dose rate with MCNP5 in external radiation therapy when I haven't activity and total NPS thanks in advance ?

Hello;

I am using MCNP5 to calculate the dose for some luminescent radiation detector such as RPL , TLD- or OSL in radiotherapy (Mega-voltage and electron beam) use F6 tally, so it becomes dose/(particle source)

I found a difficult to calc