# Monitor Unit Calculation Practice Problem

A patient is being treated with radiation therapy using a SAD of 100 cm and
a square field size of 8.9 cm^{2} at the isocenter. 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 10.5 cm (at the isocenter), 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 = 10.5 \: cm, SSD = 100 \: cm) |

8.0 | 0.992 | 0.996 | 64.2 |

8.9 | 0.996 | 0.998 | 65.0 |

9.0 | 0.996 | 0.998 | 65.1 |

10.0 | 1.000 | 1.000 | 66.1 |