[ 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.


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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