Brachy Flashcards
Are sources sealed or unsealed?
sealed
What is dose homogeneity
Some parts of tumour will receive much high dose than other parts.
4 Methods of classifying Brachy
Treatment Duration
Dose rate
Radioactive source placement
Loading method
What dose rate is used for permanent brachy seeds?
Low Dose Rate
LDR
Which dose rates would the radioactive source have a long half life and why?
HDR as the dose rate would be more ‘steady’ due to the longer falloff times for radioactive decay.
Remember that in HDR the source will be removed afterwards.
Which LDR radioactive source is traditionally used ? and which has better radiobiology?
Traditionally used: Iodine - 125
Radiobiology: Cesium 131
Commonly used HDR source?
Iridium 192
What type of decay is preferable for Brachy?
No charged particle emission
( beta particle emission can however be filtered out).
no radioactive daughter product
Approximately what is the decay energy of Ir-192
0.4 meV
What is the approximate energy of the isotopes commonly used in low dose rate
(LDR) brachytherapy?
30 keV
What is the SI unit for source strength?
Air kerma rate (μGy h-1 m2)
Why is the source measured in radioactive per gram?
Amount of radiation given out per gram.
This is because we need a high level of radioactive in a small substance so it can fit in the needle.
It also needs to be non toxic and easily shaped.
Where is permanent brahy treatments traditionally placed?
interstitial
intraluminal
Into oesophagus, bronchus.
vascular
Into blood vessels
What type of loading is used in LDR?
Manual Afterloading
Which term SHOULD be used in Brachy when referring to radioactive decay of the source?
Source strength as it uses the air kerma rate as its SI
H 1/2 of Iodine 125
60 days
H1/2 of most LDR isotopes
74.2 days
Is a mono or poly energetic source preferred?
mono
SI of activity
Bq
SI of Source strength
Kerma
Why is HVL more useful in BRachy than EBRT?
Because source is mm from surrounding tissue.
Do sources emitt radiation equally in all directions?
no
