[ RadSafe ] Mutual Effects of U and T factors- Linac Room
Moshe Levita
mlevita at tasmc.health.gov.il
Sun Feb 3 10:45:02 CST 2008
Dear Colleagues,
In designing Linear Accelerator rooms one is considering the Use factor U
and Occupancy factor T .
Under certain conditions the multiplication of these two factors can be
very small.
Imagine 2 energies machine and very high leakage when the machine is operating in its
high energy mode AND maximal field size AND pointing at specific direction.
If:
The high energy fraction is : 40 % of total treatments
Direction Factor is : 10 % of all directions
Maximal field size fraction is : 20 % of all treatments
Then, Total (Use Factor) = 1/125
If the relevant Occupancy Factor is : 1/16 at uncontrolled areas - partial time
Then Use x Occ. Factors = 0.0005
These small factors might allow very high I.D.R (Instantaneous Dose Rate).
Though many experts doesn't care about limiting the I.D.R, I would like to
ask your opinion about any known limitation on the Use x Occ. Factors ?
e.g why not limiting the Use x Occ. Factors to be > 1/64 or other value ?
Thank you,
Moshe Levita
Chief Physicist
Tel Aviv Medical Center
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