Brachy Flashcards
is a method of treatment in which sealed radioactive sources are used to deliver radiation at a short distance by interstitial, intracavitary, or surface application.
Brachytherapy
With this mode of therapy, a high radiation dose can be delivered locally to the tumor with rapid dose falloff in the surrounding normal tissue.
Brachytherapy
In the past, brachytherapy was carried out mostly with ____ or ___ sources.
radium, radon
Currently, use of artificially produced radionuclides in brachytherapy such as _______ is rapidly increasing
137Cs, 192Ir, 198Au, 125I, and 103Pd
New technical developments have stimulated increased interest in brachytherapy: the introduction of _____ to reduce personnel exposure, and automatic devices with remote control to deliver controlled radiation exposure from high-activity sources.
artificial isotopes, afterloading devices
is the sixth member of the uranium series, which starts with 238U-92 and ends with stable 206Pb-82.
Radium
Radium disintegrates with a half-life of about ____ to form radon
1,600 years
As a result of the decay process from radium to stable lead, at least 49 γ rays are produced with energies ranging from _____ MeV.
0.184 to 2.45
The average energy of the γ rays from radium in equilibrium with its daughter products and filtered by 0.5 mm of platinum is ____ MeV.
0.83
The radium is supplied mostly in the form of _____ that is mixed with an inert filler and loaded into cells about 1 cm long and 1 mm in diameter.
radium sulfate or radium chloride
The radium is supplied mostly in the form of radium sulfate or radium chloride that is mixed with an inert filler and loaded into cells about _____
1 cm long and 1 mm in diameter.
These radium cells are made of ____ and are sealed to prevent leakage of radon gas.
0.1- to 0.2-mm-thick gold foil
Radium sources are specified by
Active length
Physical length
Activity or strength of source
Filtration
Three types of radium needles used for implants:
Needles of uniform linear activity, needles with higher activity at one end (Indian club), and needles with high activity at both ends (dumbbell).
is a γ-ray–emitting radioisotope that is used as a radium substitute in both interstitial and intracavitary brachytherapy.
Cesium-137
The main advantages of 60Co is its ____, which allows fabrication of small sources required for some special applicators.
high specific activity
Cesium-137 is supplied in the form of _____, labeled with 137Cs, and doubly encapsulated in stainless steel needles and tubes.
insoluble powders or ceramic microspheres
The advantages of 137Cs over radium are
it requires less shielding and is less hazardous in the microsphere form
With a long half-life of about 30 years, these sources can be used clinically for about 7 years without replacement, although the treatment times have to be adjusted to allow for radioactive decay (2% per year).
Cesium-137
137Cs emits γ rays of energy____ MeV
0.662
has been used for brachytherapy but is rarely used now
60Co
Disadvantages of Cobalt-60
more expensive than 137Cs and has a short half-life (5.26 years)
Cobalt brachytherapy sources are usually fabricated in the form of a ___ that is encapsulated in a _____.
wire, sheath of platinum iridium or stainless steel
Curie-sized cobalt sources have also been used in a unit called the ____
Cathetron (11,12,13)
This is a remote-loading device and provides high dose rates for intracavitary therapy, for example, 250 to 300 cGy/min at point “A”
Cathetron
sources are fabricated in the form of thin flexible wires that can be cut to desired lengths.
Iridium-192
192Ir has a complicated γ -ray spectrum with an average energy of ____
0.38 MeV
192Ir has the disadvantage of a short half-life ____
73.8 days
198Au has a half-life of ____ and emits a monoenergetic γ ray of energy _____
2.7 days, 0.412 MeV
has gained a wide use for permanent implants in radiation therapy.
125I
Advantages of 125I
long half-life (59.4 days)
low photon energy which requires less shielding
seeds have recently become available for use in brachytherapy.
103Pd
Half-life of Palladium-103
17 days
was developed to deliver uniform dose (within ±10%) to a plane or volume.
Paterson-Parker or Manchester system
The system specified rules of source distribution to achieve the dose uniformity and provided dosage tables for these idealized implants.
Paterson-Parker or Manchester system
In the case of planar implants the uniformity of dose is achieved in parallel planes at ____ from the implanted plane and within the area bounded by the projection of the peripheral needles on that plane.
0.5 cm
The spacing of the needles ____ from each other or from the crossing ends.
should not be more than 1 cm
is composed of belt, four parts; core, two parts; and each end, one part
Cylinder
is made up of shell, six parts, and core, two parts
Sphere
consists of each side, one part; each end, one part; and core, two parts.
Cuboid
•Uses sources of uniform linear activity
•Sources distributed uniformly over the area or volume
•Result is non-uniform dose distribution, higher in the central region
Quimby System
is an extension of Quimby system.
Memorial system
was used for manual intra-operative planning of I-125 implantation
Memorial Nomogram
Developed based on experience with Ir-192 interstitial implants by afterloading techniques
Paris System
forms the basis for dosimetry
BASAL DOSE (BD)
Similar to Paris and Quimby techniques
Computer System
Brachytherapy sources are applied in three ways:
1.External applicators or molds
2.Interstitial implantation
3.Intracavitary therapy
are used to treat small superficial areas, such as the ear or the lip.
Surface molds
is indicated when the tumor is well localized and can be implanted directly according to accepted rules of distribution;
Interstitial therapy
is used when applicators containing radioactive sources can be introduced into body cavities. In all these cases, owing to the short treatment distance, the geometry of source distribution is critical.
Intracavitary therapy
two types of interstitial implants:
1.Temporary
2.Permanent
–The sources are removed after the desired dose has been delivered (e.g., radium needles, iridium wires, or iridium seeds).
–Provides better control of source distribution and dosimetry than a permanent implant
Temporary implant
–The sources are left permanently in the implanted tissues (e.g., 198Au and 125I seeds).
–A one-time procedure and is a preferred method for some tumors such as those in the abdominal and thoracic cavities.
Permanent implant
This procedure eliminates exposure in the operating room, the x-ray room, and the areas through which the patient is transported. “Dummy” sources are used for radiographic localization and dosimetry.
Interstitial Therapy
is mostly used for cancers of the uterine cervix, uterine body, and vagina. A variety of applicators have been designed to hold the sources in a fixed configuration.
Intracavitary therapy
–Applicator is pre-loaded and contains radioactive sources at time of placement into the patient.
Hot loading
–Applicator is placed first into the patient and the radioactive sources are loaded later
–Either by hand (manual afterloading)
–Or by machine (automatic remote afterloading)
Afterloading
Radium is the sixth member of the uranium series, which starts with ____ and ends with stable ____
238U-92
206Pb-82
The product nucleus ___ is a heavy inert gas that in turn disintegrates into its daughter products.
radon
○ The distance between the ends of the radioactive material
Active length
○ The distance between the actual ends of the source
Physical length
○ Milligrams of radium content
Activity or strength of source
○ Transverse thickness of the capsule wall, usually expressed in terms of millimeters of platinum
Filtration
Linear activity of a source can be determined by
dividing the activity by the active length
○ needles with higher activity at one end
INDIAN CLUB
○ needles with high activity at both ends
DUMBBELL
Uniform linear activity needles may be
_____
Needles also are constructed with linear activities of ____
0.5 and 0.25 mg/cm
