Question 20 of 30

(demo test)

Product Demo for Clinical

For a 6 MV beam, ROF for field size 20x20 cm² is 1.055 and ROF for field size 15x15 cm² is 1.035. The equivalent square for your MU calculation is 18x18 cm² . What is the ROF value you need?

A. 1.063

B. 1.027

C. 1.047

D. 1.043

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Category:

Radiation Physics

Topic:

Dosimetry

High Yield:

Yes

Your Answer:

U

Correct Answer:

C

Explanation:

In order to find the ROF value we need to do a linear interpolation calculation. This assumes that the relationship can be appoximated as a straight line. However, when points are close, it is a valid appoximation.

If we are finding value (x,y) that is located between known values of (x₁,y₁) and (x₂,y₂)

y=y₁+((x-x₁)/(x₂-x₁))*((y₂-y₁)

ROF (18x18 cm²)=1.055+((18-20)/(15-20))*(1.035-1.055)=1.047

Reference: P. MacDermontt, C. Orton "The Physics and Technology of Radiation Therapy", section 10.8

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