USRBDX results for SOBP

Dear FLUKA experts,
I’m performing calculations for proton therapy. When calculating the beam utilization at SOBP, I chose to use the USRBDX card to calculate 90% of the maximum value of the front end as the number of particles that just entered the SOBP region.

From the instructions I learned the difference between fluence and currents, I chose l2,linE,linΩ to calculate the number of protons on this plane, and then divided by the calculated number of particles to get the beam utilization rate.

I wonder if there is any problem with calculating the beam utilization in this way.

Thank you for your guidance.

Kind regards,
Niko