Radioactive Sources Flashcards
Low dose rates (LDR) range from
40 to 80 cGy/h
High dose rates (HDR) start at
20 cGy/min
Sources for permanent implants should have
a short half-life to minimized radiation to public.
Sources for permanent implants should have
low energy radiation so that radiation does not easily escape patients.
Most sources used for brachytherapy are
sealed sources.
Activities for LDR sources range
0.1 to 100 mCi.
Activities for HDR afterloaders units can be as high as
10 Ci.
Radium-226 is difficult to
shield due to its high mean energy.
The disadvantages of using radium are:
Hard to shield due to its high mean energy of 0.83 MeV and radon gas leak.
One gram of radium has an activity of
1 Ci.
Cesium-137 is a HDR or LDR source?
LDR
Cesium-137 is predominantly used for
cervical cancer.
Cs-137 advantages over Radium-226 are
Uses less shielding and has no radon hazard.
What are Cs-137 Half-life, mean energy, and HVL?
30 years, 0.662 MeV, and 5.5 mm
High energy sources have identical dose distribution within 10 cm because
absorption and out scattering is compensated by in scattering, which leads to dominating inverse square effect.
What are Ra-226 Half-life, Mean energy, and HVL?
1600, 0.83 MeV, and 16 mm.
Iodine-125 is used for permanent implants of
the brain and prostate.
Additionally, I-125 can be used on the eye as
temporary eye plaques.
What are I-125 Half-life, mean energy, and HVL?
60.2 days, 28 keV, 0.025 mm.
The dose distribution of I-125 is highly anisotropic due to
its low energy of radiation.
Iridium-192 is a HDR or LDR source?
HDR
Ir-192 is commonly used for
temporary interstitial transplants.
What are Ir-192 Half-life, mean energy, and HVL?
73.8 days, 0.38 MeV, and 2.5 mm.
Ir-192 specific activity is
450 Ci/g
Ir-192 is well suited for
HDR afterloaders.
When patients are treated with Cs-137 brachytherapy sources, the dose deposited at 1 cm in tissue is from
Gamma only
What are the photon energy for the following sources:
Cs-137
I-125
Ir-192
Co-60
0.662 keV
30 keV
- 380 keV
- 25 MeV
The dose distribution in tissue up to 5 cm from an Ir-192 seed can be predicted from inverse square alone because:
Absorbed and out scattered photons are compensated by in scattered photons at a given point P
I-125 seed are used in brachytherapy for their
x-ray and gamma rays.
Half-life for radioisotopes:
I-125
Cs-137
Co-60
Palladium-103
60 days
30 years
5.26 years
17 days
Radionuclide which emits photons of average energy of 21 keV and has a 17 day half-life is:
Pd-103
