Treatment planning

Question 1

What is the relationship between and intensity and distance?

Answer 1

Inversely proportional

Effect of a torch as you go further away field size becomes larger

Question 2

What are some interactions with matter?

Answer 2

Photoelectric effect
Compton scatter
Pair production

Question 3

What are isodose curves?

Answer 3

Lines passing through points of equal dose

Question 4

Lower energy beams do what?

Answer 4

All dose on the surface and bulging isodose curves

Question 5

Higher energies do what?

Answer 5

Travel further and deposit energy further in the patient

Question 6

What is dmax?

Answer 6

Maximum absorbed dose occurs for single field photon beams

Question 7

Dmax depths?

Answer 7

200kv -0
4mv-1
6mv-1.5
10Mv-2.5
18Mv-3.5

Question 8

As the energy of electrons increases their range does what?

Answer 8

It increases

Question 9

What can a bolus be made out of?

Answer 9

Wax jelly vas gauze

Anything tissue equivalent

Question 10

What is field size defined as?

Answer 10

Lateral distance between the 50% isodose curves at a reference point

Question 11

What are minimum and maximum field sizes?

Answer 11

4x4

And 40x40

Question 12

How do you increase field size?

Answer 12

By increasing distance

Question 13

Low energy beams have what?

Answer 13

Greater lateral scatter

Question 14

Orthovoltage beams have increased scattered dose to what?

Answer 14

Surrounding tissue

Question 15

What is penumbra?

Answer 15

Edge of radiation beam where dose rate changes rapidly

Area of unsharpness

Question 16

What does a larger source size do to penumbra?

Answer 16

Larger penumbra

Question 17

Factors of penumbra?

Answer 17

Source size
SSD
Position of collimators closer the collimator less penumbra
Effects of scatter in the patient

Question 18

To reduce penumbra for subclav fields what can you do?

Answer 18

Create a zero jaw

Question 19

What is the penumbra defined as?

Answer 19

Between 20 and 90 % isodose curves

Question 20

What is transmission penumbra?

Answer 20

Occurs as radiation passes through the edge of primary collimators therefore secondary collimators are used?

Question 21

What is exit dose?

Answer 21

Amount of absorbed dose emerging from phantom or patient

Question 22

Dmax occurs where for lower energies?

Answer 22

Closer to skin

Deeper for higher energies

Question 23

Orthovoltage causes what?

Answer 23

Increased scattered dose to tissue around treatment site