Brachytherapy Flashcards
four types of BT
interstitial
intra-cavity
intra-luminal
surface applicators
intra-cavity
most common
placed in pre-exisiting body cavity
temp implant
images are captured to make sure implant is positioned correctly
interstitial
positioned surgically into tissue
sources must have small diameter
breast, tongue, anus, prostate
temp or permanent
positioned via remote after loading equipment returned to the source safe afterwards
surface applicators
treats the body surface
maintained at a short distance
useful in malignancies overlay sensitive tissue
superficial malignancies
temp
intra-luminal
positioned in the lumen
only HDR
bronchus and oesophagus
temp
properties of an ideal source
high specific activity
gamma energy approx 0.5MeV
small and flexible
half life is long enough correction for decay is minimal
what is temp source
when the radioactive source is placed in the body for a period of time which is then removed, only for treatment.
energy of the sources is normally over 0.5MeV
what is permanent source
placed inside or near the tumour which is not removed.
short half life and low energy
implantation pattern is specific to the tumour
more limited with the type of BT
what is a sealed source
radioactive material which is either permanently sealed in a capsule or bonded closely in solid form
EITHER PARTICLES OR GAMMA RAYS NOT BOTH
when can a gamma ray source be used
if the particles are removed capitulating the source removes the beta particles
what does a metal encasement do
prevent escape of the material, particularly any gaseous daughter products
absorb alpha and beta particles formed in the decay process
what is the only source which is not sealed
IRIDIUM-192
SOURCE IS RELEASED WHEN WIRES ARE CUT
describe BT for prostate gland
reached via the perineum, it is confided to this area, to reduce effects . Guide needles are placed into the prostate via a template which is attached to the perineum, once in the right position plastic applicators are threaded through the guide needed, imaging checks position
what is used for pelvic regions
gamma rays
what is the role of the capsule in pelvic regions
removes the gamma rays which shields the patient, gamma rays are emitted from the nucleus. The energy is dependent on the source
what is the energy that radiation protection has to be provided for
1.33 MeV
what are orphan sources
not managed by an authorised body
high activity sealed sources
controlled by right laws
high radiation output
potentially hazardous
BSSD have requirements for maintaining accurate and up to date records of location, composition and activity level of HASS
cat 1
death or severe injury if in close contact for a short period of time
cat 2
in contact longer than cat 1: industrial gamma radiography, HDR brachytherapy
cat 4
temp injury, longer period than cat 3, permanent injuries are unlikely
LDR brachytherapy
loading
describes how sources are loaded into their applicators and placed in the body
pre loading
positioning applicators into the body with rs loaded, no imaging
after loading
empty applicators are loaded into the body, image to check position before active sources are placed into the patient
what are the types of AL
remote
manual
loaded by hand
loaded under computer control
what is a LDR dose rate
0.4-1/2 Gy/hour (Caesium-137 and iridium- 192)
what is a medium dose rate
2-12Gy/ hour
what is a HDR
> 12Gy/hour (iridium-192 and cobalt-60)
PDR
it is a combination of HDR & LDR
LDR has long treatment time and uncomfortable whereas HDR is quicker
it is a LDR treatment which is stimulated by pulses each pulse in 10 minutes with an hour interval
higher number of fractions than HDR, lower risk of overdosing
in-between pulses restrictions are lifted
temp has what dose rate
high
describe the use of stable iridium
it is placed in a neutron influx, the longer its left the more stable neutrons are able to become unstable
increasing specific activity means less source is required
higher number of iridium converted means a higher activity to the source as the concentration of unstable atoms is higher
HDR has more or less half life
less
LDR has more or less half lives
more
shielding
room design, observation via camera, temp safe for short term storage and emergency
time: temporary
ensure no overdose
dependent on DR
individual calculation
if staff needs to enter it is timed
procedure:
source leaves AL equipment, moving into the body, remains for the calculated period of time
radiographer never handles the source
safe unless source gets stick
time: permanent
RS remains in situ: not removed
isolation, emitting gamma rays constantly
isolated period is calculated
time limits are set for contact
gamma rays are low energy measured in Kev
distance
achieved by forceps, never handle applicators of transfer tubes
remote AL
confirmation of source position
inserted into applicator system
no exposure to staff
manual AL
confirmation of source position
operator inserts onto position
staff will receive a measurable dose
regular updates
equipment for protection
min exposure to staff
requirements for remote
accurate control of source position
source positon indicator
small physical size source
flexible short source transit tubes [source-transit system, gets source from safe to applicator]
automated return of source
backup power supply
exposure warning system
low transit dose
automated computerised correction for source decay
computerised controlled planning
safe
AL components
source safe
source transit system
applicator system
safety system
HDR advantages
minimal discomfort
treatment time is in minutes
all four types can be used
high number of treatments can be completed in a day
source replacement is infrequent Co-60 every 4 years
cost per patient is low
day case patients
radiation safety improved
no visiting restrictions
HDR disadvantages
if an issue exposure is> than LDR
shielding requirements if Co-60 is used
regular source replacement for iridium- 192
radiobiology
LDR advantages
low levels of discomfort
radiobiologically
range of applicators for intracavity
low staff exposure
dual channel equipment, can treat two patients at the same time
tissue exposure< HDR
caesium working life is 20+ years
shielding requirements are less than Co-60
LDR disadvantages
less patients through each day
treatment is measured in hours
doesn’t treat intra-luminally
cost per treatment is high
iridium-192 regular replacements
discomfort
visiting is required
HDR: microelectron
heavy safe used, depends on the source type
mobile unit: transports machine
source travels from source safe to temp safe = holding part
end part: source leaves the machine
separate control panel
curation
6 channels
fewer patients can be treated
stepping sources
remote AL equipment = IRS
source is programmed to travel through the prescribed applicators
sources move in steps inside the applicator delivering dose as it moves
for every step, the source is programmed to remain in position for a period of time DWELL position
source is found at the wire tip
flexitron: elekta
mobile unit: motor controlled
RS leaves the top
tungsten safe: protects up to 20Ci source to max 22Ci source
20 treatment channels, each channel takes the source out of the machine into the patient
each channel has an interlock
iridium-192, Yttritum-169 dual or single source
used for HDR, LDR
radiobiology
very steep dose rates around implanted sources
normal tissues receive lower doses than EBRT
LDR provides sub-lethal damage, allowing for recovery
treatment distance is 1-2cm, doubling distance quarters the intensity
LDR= more cells survive than oxygenated tumours as they repair more easily
HDR = better at killing oxygenated tumour cells, therefore better at killing tumours
where is recurrence likely
hypoxic región, more cells survive in HDR, due to sub lethal damage being continuous, overtime this accumulation causes damage
what does PDR mimic
LDR and HDR
