Beam Geometry Part 2

Question 1

Inverse square law

Answer 1

The ISL states that the intensity of the beam (from a point source) varies inversely with the square of the distance from the source

Question 2

Fluence

Answer 2

Number of photons per cross sectional area

Question 3

Dose rate is related to the intensity of the beam

Answer 3

Dose rate is inversely proportional to the square of the distance

Question 4

Penumbra

Answer 4

A partial shadow
Area of fuzziness from the beam axis

There is
Geometric penumbra
Transmission
Physical

Question 5

Geometric penumbra

Answer 5

Caused by the size of radiation

Depends on size of source and diaphragm distance (SDD)

Question 6

Transmission penumbra

Answer 6

Region irradiated by photons that are transmitted through the edge of collimator block

Question 7

Physical penumbra

Answer 7

Fuzziness at edge of the beam that is actually measured in the patient