# 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
t_{0} = d_{max} = 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) |

13.4 | 1.014 | 1.007 | 43.9 |

14.9 | 1.020 | 1.010 | 44.5 |

15.2 | 1.021 | 1.010 | 44.6 |

17.7 | 1.031 | 1.015 | 45.6 |