Evaluate only one CASE WHEN in a select

Hi everybody,

I'm implementing something like this:

SELECT
CASE WHEN add_numbers(t1.main_number,t2.main_number)>100
THEN t1.description1
ELSE t2.description1
END AS number_description1,
CASE WHEN add_numbers(t1.main_number,t2.main_number)>100
THEN t1.description2
ELSE t2.description2
END AS number_description2
FROM table1 t1, table2 t2;

Is there a way to evaluate the 'CASE WHEN' only once?

Thanks

Daniel