Monitor Unit Calculation Practice Problem
A patient is being treated with radiation therapy using a SSD of 98 cm and
a rectangular field size of 13.4 cm by 16.8 cm at the surface. The SAD for this machine is 100 cm. The medical linear accelerator is calibrated to deliver 1 cGy/MU at a depth
t0 = dmax = 1.5 cm, using a setup SSD of 100 cm and a field size
of 10 cm x 10 cm. What is the number of monitor units (MU) required to deliver an absorbed
dose of 200 cGy to a depth of 18.6 cm, on the central axis of the beam?
**Use the data provided below for square field sizes. (You will not need all the data provided, and some data may need to be derived using the F factor or the TMR/PDD conversion equation.)
|Field Size (cm)||S_c||S_p||PDD(d = 18.6 \: cm, SSD = 100 \: cm)|