Radioactive Sources

Question 1

Low dose rates (LDR) range from

Answer 1

40 to 80 cGy/h

Question 2

High dose rates (HDR) start at

Answer 2

20 cGy/min

Question 3

Sources for permanent implants should have

Answer 3

a short half-life to minimized radiation to public.

Question 4

Sources for permanent implants should have

Answer 4

low energy radiation so that radiation does not easily escape patients.

Question 5

Most sources used for brachytherapy are

Answer 5

sealed sources.

Question 6

Activities for LDR sources range

Answer 6

0.1 to 100 mCi.

Question 7

Activities for HDR afterloaders units can be as high as

Answer 7

10 Ci.

Question 8

Radium-226 is difficult to

Answer 8

shield due to its high mean energy.

Question 9

The disadvantages of using radium are:

Answer 9

Hard to shield due to its high mean energy of 0.83 MeV and radon gas leak.

Question 10

One gram of radium has an activity of

Answer 10

1 Ci.

Question 11

Cesium-137 is a HDR or LDR source?

Answer 11

LDR

Question 12

Cesium-137 is predominantly used for

Answer 12

cervical cancer.

Question 13

Cs-137 advantages over Radium-226 are

Answer 13

Uses less shielding and has no radon hazard.

Question 14

What are Cs-137 Half-life, mean energy, and HVL?

Answer 14

30 years, 0.662 MeV, and 5.5 mm

Question 15

High energy sources have identical dose distribution within 10 cm because

Answer 15

absorption and out scattering is compensated by in scattering, which leads to dominating inverse square effect.

Question 16

What are Ra-226 Half-life, Mean energy, and HVL?

Answer 16

1600, 0.83 MeV, and 16 mm.

Question 17

Iodine-125 is used for permanent implants of

Answer 17

the brain and prostate.

Question 18

Additionally, I-125 can be used on the eye as

Answer 18

temporary eye plaques.

Question 19

What are I-125 Half-life, mean energy, and HVL?

Answer 19

60.2 days, 28 keV, 0.025 mm.

Question 20

The dose distribution of I-125 is highly anisotropic due to

Answer 20

its low energy of radiation.

Question 21

Iridium-192 is a HDR or LDR source?

Answer 21

HDR

Question 22

Ir-192 is commonly used for

Answer 22

temporary interstitial transplants.

Question 23

What are Ir-192 Half-life, mean energy, and HVL?

Answer 23

73.8 days, 0.38 MeV, and 2.5 mm.

Question 24

Ir-192 specific activity is

Answer 24

450 Ci/g

Question 25

Ir-192 is well suited for

Answer 25

HDR afterloaders.

Question 26

When patients are treated with Cs-137 brachytherapy sources, the dose deposited at 1 cm in tissue is from

Answer 26

Gamma only

Question 27

What are the photon energy for the following sources:

Cs-137

I-125

Ir-192

Co-60

Answer 27

0.662 keV

30 keV

0. 380 keV
1. 25 MeV

Question 28

The dose distribution in tissue up to 5 cm from an Ir-192 seed can be predicted from inverse square alone because:

Answer 28

Absorbed and out scattered photons are compensated by in scattered photons at a given point P

Question 29

I-125 seed are used in brachytherapy for their

Answer 29

x-ray and gamma rays.

Question 30

Half-life for radioisotopes:

I-125

Cs-137

Co-60

Palladium-103

Answer 30

60 days

30 years

5.26 years

17 days

Question 31

Radionuclide which emits photons of average energy of 21 keV and has a 17 day half-life is:

Answer 31

Pd-103