Introduction to Brachytherapy Flashcards
(36 cards)
What is brachytherapy?
The use of radioactive sources at close distances to treat various tumours.
Name the 3 most common types of brachytherapy
1) Surface moulds
2) Interstitial
3) Intracavity
Name 1 tumour type that surface mould brachytherapy treats
Skin cancer
Name 1 tumour type that interstitial brachytherapy treats
Prostate
Name 1 tumour type that intracavity brachytherapy treats
Cervical
Why is brachytherapy beneficial?
Because it is a localised treatment that gives a high dose near to the radioactive source but has a rapid fall off further away, meaning that it is suited to tumours surrounded by many OAR.
State 9 properties of an ‘ideal’ brachytherapy source
1) 0.2-0.4 MeV Energy range
2) Suitable half-life
3) No (or easily screened) charged particle emission
4) No gaseous decay
5) High specific activity
6) Chemically non-toxic and insoluble
7) Mechanically stable
8) Easily moulded and formed into different shapes
9) Sterilisable
Should a temporary brachytherapy implant have a short or long half-life? Why?
Short with high activity as it will be removed before the patient is discharged, so it needs to deliver enough dose.
Should a permanent brachytherapy implant have a short or long half-life? Why?
Long with low activity so that the patient can leave without irradiating others.
Which radioisotope is most commonly used for LDR brachytherapy?
Caesium-137
Which radioisotope is most commonly used for HDR brachytherapy?
Iridium-192
Which radioisotope is most commonly used for brachytherapy prostate seeds?
Iodine-125
Which radioisotope is most commonly used for brachytherapy eye plaques?
Ruthenium-106
Why is Ir-192 suitable for HDR treatments?
1) Long half-life
2) High specific activity
3) Decay mode = 95% beta minus and 5% electron capture with gamma emission
4) Average decay energy of 380 keV
Define afterloading
The ability to deliver a radioactive source into a catherter or applicator after it has been correctly positioned for treatment.
How does manual afterloading work?
The applicator is positioned correctly then the sources are manually loaded into the applicator, minimising the radiation exposure to staff.
What are the 2 types of remote afterloading?
Low dose rate
High dose rate
How does remote LDR afterloading work?
The applicators and the after-loading machine form a closed system when they are attached. A pressure system forces the pellets from the safe into the applicators in trains, often under positive air pressure.
True or false: LDR treatments no longer use afterloaders in the UK.
True
How does remote HDR afterloading work?
A single stepping source system moves the source to pre-determined positions using a stepper motor/cable system.
State the 5 HDR treatments that use afterloaders
- Intracavitary
- Interstitial
- Intraluminal
- Intravascular
- Intraoperative
State 8 safety features of a HDR afterloader
1) Back-up secondary timer system
2) Automatic check of the transfer tube/catheter system before the source is exposed
3) Distance check
4) Operating system to check that the source has returned properly
5) Back-up power supply
6) Manual source return in the event of complete power failure
7) Automatic retention of treatment data and history in the event of power failure
8) Alarm and status code system to alert user to faults
State 8 safety features of a HDR treatment room
- A dedicated, protected room suitable for the energy of the source used
- Thick concrete walls, maze entrance
- Careful maze design (as radiation is not collimated)
- Control desk outside treatment room
- Will be a ‘controlled area’ under IRR regulations
- Radiation warning lights (independent of the machine)
- Interlock barrier at room entrance(s)
- Audible alarm when the source is exposed
How often are HDR sources calibrated?
When there is a new source and during routine quarterly services
