Question 22 of 30

(demo test)

Product Demo for Clinical

A patient is to be treated with a single isocentric field at 100 cm SSD. The dose per fraction is 300 cGy with 6MV photons to a depth of 8cm with a 12x12 cm² field. The PDD is 0.760, ROF is 1.017 and the dose rate at central axis for a 10x10 cm² field at 100 cm SAD at dmax is 0.967 cGy/MU. What is the MU setting needed to treat this field?

A. 401

B. 415

C. 358

D. 374

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Category:

Radiation Physics

Topic:

Dosimetry

High Yield:

Yes

Your Answer:

U

Correct Answer:

A

Explanation:

For fixed distance setup on central axis, assuming that tray factor is 1.0 

MU= dose/(PDD*ROF*InvSq*Dose Rate)

Since the problem states that the field was setup at 100 cm SAD, InvSq=1.0 

Then

MU=300 cGy / (0.760*1.017*1.0*0.967 cGy/MU) = 401 MU

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