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Brachytherapy

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Characterized by dose rates as high as 400 cGy/min
HDR
Characterized by dose rates of 40 - 200 cGy/hr
LDR
Which surgical brachytherapy implant technique may include permanent seeding?
Interstitial
Name the two commonly used sealed LDR sources.
Cesium 137 and Iridium 192
Name commonly used sealed source for HDR.
Iridium 192
Name the three sources used for permanent seeding in brachytherapy.
Iodine-125, Pd-103, Gold-198
Which system of interstitial implants is characterized by a uniform distribution of sources with intersource spacing of 1 cm?
Quimby
Which system of interstitial implants defines the stated dose as the maximum dose in the specified plane?
Quimby
Which system of interstitial implants defines the specified dose in a plane 0.5 cm from the implant plane and 10% higher than the minimum dose in the implant plane?
Manchester or PP
The philosophy of this implant system is to achieve a +/- 10% dose uniformity in the specified plane.
Manchester or PP
Which system of interstitial implants is characterized by constant linear activity of the implant sources?
Quimby and Paris
Which system of interstitial implants does not use crossing needles and why?
Paris. System uses active needle lengths 40% longer than target tissue.
Which system of interstitial implants is characterized by a spacing ratio of planar implants depending on target size?
Manchester Or PP
Which system of interstitial implants was developed for removable implants of long lines of sources?
Paris
Which system of interstitial implants technically works well for small implants such as Ra needles?
Manchester or Quimby
Why can't Quimby tables be applied to Ir-192 implants, even though they are equal intensity sources?
Differing geometrical shapes
Define the basal dose used to calculate the reference isodose for the Paris system.
(85% of ...) The average of minimum doses between all sources.
Define point B as used in the Manchester system for cancer of the uterus and its anatomical significance.
3 cm lateral to point A, represents level obdurator nodes
What reference points are used for calculation dose in the ICRU system for intercavitary brachytherapy?
Bladder and rectal wall points, lymphatic trapezoid, and pelvic wall points
How is total source strength defined in the ICRU system for intercavitary brachytherapy?
As total reference air kerma as a 1-m distance.
Dose distribution in tissue for brachytherapy sources follow the inverse square law because...
scatter dose build up and attenuation cancel each other out
radioactive sources used in tandem and ovoids are in this shape
tubes
radiactive sources used in tandems and ovoids
Cesium 137
Define point A for gyno implants
2 cm cephalad of external cervical os and 2 cm lateral uterine tandem
Isotope most frequently used in nasopharyngeal implants
Cesium 137
Radionuclide w energy 370 keV
Ir - 192
Radionuclide with energy 410 keV
Gold 198
Energy Pd 103
21 keV
Energy gold 198
410 keV
Radionuclide w energy 29 keV
I-125
I 125 used as what?
Perm implant
Cs 137 used for what?
tandem and ovoids, LDR
Ir 192 used for what?
LDR HDR
What kind of specific activity is needed by sources in HDR?
High specific activity
Typical initial dose rate in Pd 103
20 cGy/min
How is Sr 90 made
fission by-product nuclear reactor
Typical volume for dose chamber used to calibrate brachy source
100 cm3
Typical source length for pellet in vascular brachy
3 mm
How is a batch of seeds calibrated?
Average activity is taken to find activity per seed
Half life Sm 145
1 year
define apparent activity
activity source, taking into account abs and atten in encapsulated material
Sr 89 is used even as an unsealed source because...
electrons have max energy 1.5 MeV
What type of emitters in vascaular brachy?
beta or gamma
End result of Ra 226 decay series is stable:
Lead 206
Typical activity of C0 60 used in remote afterloaders
1 - 10 Ci
How is Gold 198 made?
Gold 197 bombarded w neutrons in reactor
Periodicity for autoradiographing source in remote afterloader
quarterly
Typical activity Cs 137 used for remote afterloaders
40 mCi
When can a patient with seeds leave hospital?
Dose at 1 meter less than 5 mR/hr
How is effective half life of source determined?
function of physical and biological half life
How is Pd 103 made?
Bombard Rh 103 with proton in cyclotron
Which radiopharmaceutical consists of tiny spheres in a liquid
Y 90

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