Brachytherapy Exam 1 Practice Questions
The placement of a sealed radioactive source into or immediately adjacent to a tumor is known as
"brachytherapy"
Two gamma-rays in each disintegration.
(1.17MeV and 1.33MeV) giving average energy of 1.25 MeV.
Depending on the half-life of the material, the sources may be removed after a few minutes
(HDR)
Depending on the half-life of the material, the sources may be removed after days
(LDR) or permanent implants.
Iodine-125 average energy
0.028 MeV.
Iridium-192 Gamma ray emitted with an average energy of
0.38 MeV.
Cesium-137 has an Average energy and half-life of:
0.662MeV, half-life of 30 years.
The gamma rays that are emitted when Radium decays have an energy of what?
0.83MeV.
The curie (Ci) is defined as
1 Ci = 3.7 x 1010 disintegrations/sec.
What is the energy of the two gamma rays emitted from the decay of Cobalt 60?
1.17 & 1.33 MeV
Radium-226 Extremely long half-life of
1600 years.
Half life of Palladium-103
17 days
Gold-198 half-life
2.7 days
Iridium-192 is Also used in HDR units with an approximate length of
3 mm and 0.5 mm in diameter.
Cobalt-60 half-life
5.26 years.
Iodine-125 half-life
59.4 days
Iridium-192 half-life of
73.83 days
For radium the exposure rate constant is
8.25 Rcm2 /mg-hr
Cesium-131 half-life is
9.7 days.
When doing calculations to find activity remaining after some time has elapsed uses the following formula.
A==A0 e-λt
____________uses the rapid falloff of radiation intensity produced by the inverse square law.
Brachytherapy
can be a single mode of treatment or used in combination with external beam as a boost.
Brachytherapy
keeps the doses high to the tumor and low to critical structures and the healthy tissues.
Brachytherapy
Which isotope has an average energy of 662 keV?
Cesium 137
Available as seeds and comparable to I-125.
Cesium-131
Newest seed for permanent implants.
Cesium-131
Emits gamma rays, is double encapsulated in stainless steel needles and tubes.
Cesium-137
Has no decay product, therefore safer to use in clinic.
Cesium-137
What is a radium substitute used in interstitial and intracavitary implants?
Cesium-137
Also for some reusable eye plaques, and for the gamma knife.
Cobalt-60
At one time used in a unit called a Cathetron, which was a remote afterloader.
Cobalt-60
Excellent for teletherapy, due to the penetrating power.
Cobalt-60
Usually in the form of a wire, but more expensive than Cesium.
Cobalt-60
Was used at one time for brachytherapy, but rarely used now.
Cobalt-60
The ____________ is the historical measure of radioactivity.
Curie
Who were involved in the first uses of Radium.
Edison and Curie
Cesium-137 is Used mainly in
GYN malignancies.
Which isotope has the shortest half-life?
Gold 198
All activity is gone in approximately 1 month.
Gold-198
Form of seeds or grains, produced in a cyclotron.
Gold-198
Replaced radon-222 seeds, half life of 3.83 days
Gold-198
Used for interstitial implants.
Gold-198
Used in lung, bladder, prostate or brain implants.
Gold-198
Available as seeds and has advantages over radon and gold
Iodine-125
Dosimetry varies between manufacturers and need to have cross comparisons based on the seed design.
Iodine-125
For permanent implants of prostate and temporary implants such as eye plaques.
Iodine-125
Has an x-ray marker embedded to help with filming.
Iodine-125
Has a fairly short half-life, but still not suitable for permanent implants.
Iridium-192
Requires less shielding due to the lower energy.
Iridium-192
Very popular in temporary implants
Iridium-192
is Reactor produced and sent back to company.
Iridium-192
An advantage of brachytherapy over external beam is:
It spares normal tissues It delivers doses to a shorter distance It can give high doses to the tumor
There are 3 classifications of dose rate.
Low, Medium and High Dose Rate
Gold-198 is a gamma ray emitter with an energy of
Monoenergetic / 0.412 MeV.
Available as seeds
Palladium-103
For permanent implants of prostate.
Palladium-103
Has a shorter half-life than Iodine-125, therefore sometimes preferred in more aggressive cancers
Palladium-103
Has an x-ray marker embedded in between the two pellets to help with filming.
Palladium-103
Has two graphite pellets plated with in the source.
Palladium-103
The constant is expressed in terms of
R/hr at a point 1 cm from a 1 mCi point source.
It was placed in direct contact with the tumor.
Radium
Radon gas is a hazard of a broken ______________ source.
Radium 226
Which isotope has the highest energy?
Radium 226
Beta-ray emitter, that has a daughter product, yttrium-90.
Strontium-90
Foil bonded in silver, prevents the low energy particles from exiting.
Strontium-90
Used for treatment of pterygium.
Strontium-90
Radium-226 is Found in
Uranium deposits and is a decay product of U238
As Radium decays through a series it eventually becomes
a stable form of Pb-206
Patterson-Parker implant techniques were known by their:
crossing of the needles at the end of the implants
Lambda is defined as the:
decay constant
Where λ is the decay constant. The negative indicates
decreasing activity.
The Becquerel (Bq) is the unit of
disintegration. 1Bq = 1 disintegration/s
Radioactivity is usually
double encapsulated in the form of a needle, seed, wire, sphere or a source train
If the source is broken a hazard of Radium is Radon gas. To prevent this the sources are
double encapsulated.
An advantage of brachytherapy is that
high doses can be delivered in a short amount of time.
Due to the titanium end welds the distribution around Iodine-125 is
highly anisotropic.
The curie (Ci) is the
historical measure of radioactivity.
Low dose rate -
in hours and defined by dose rates between 0.4 and 2 Gy/hr
High dose rate -
in minutes, > 12Gy/hr ***note: these rates vary slightly in the textbooks
We can deliver the radiation via
intracavitary, interstitial, interluminal or surface application.
Which isotope is also used in eye plaques?
iodine 125
Brachytherapy
is a treatment where sealed sources are used to deliver radiation to a short distance.
Medium dose rate -
is in hours, >2Gy/hr but < 12 Gy/hr
Also λ =
ln 2/half-life of isotope = 0.693/t1/2
For radium the exposure rate constant is in
mg
Radium is usually manufactured in
needles or tubes and comes in a variety of lengths
Cesium-137 is Produced in a
nuclear reactor.
Radium sources can be
placed directly on or inserted into the tumor.
Consisted of a salt,
radium sulfate and mixed with a filler, usually barium sulfate in cylindrical foil cells.
Almost directly after its discovery in 1898
radium was used to treat patients.
The radioactivity is sealed inside a
shell, that prevents the escape of the radioactivity.
0.5 mm of platinum of source casing provides
sufficient absorption of all the alpha and most of the beta particles emitted by the Radium.
These Radium sources or isotopes can be embedded into
surface applicators.
By 1905, centers all over the world were implanting Radium for
temporary implants.
We use Radium as the standard for the exposure rate constant or
the gamma factor.
Activity of an isotope is defined as
the number of disintegrations per time unit (seconds, minutes, or hours).
Activity is
the rate of decay of a radioactive material
The sources were described by the
total activity, physical length, active length, wall filtration material and thickness, and diameter.
Iridium-192 Can be in the form of
wires, ribbons or single source (HDR).
Beta from the is used to treat eye lesions.
yttrium-90
