Nuclear Med Flashcards
what are the types of targeted radionuclide therapy
radionuclide itself
radioimmunotherapy: monoclonal antibodies
radio labelled microspheres: introduced into arterial circulation od tumours and provides localised radiation
small molecules which carry radionuclide
malignant pheochromocytoma
highest incidence 30-50
hereditary diagnosis: 24.9 years
sporadic diagnosis: 43.9 years
25% is hereditary
what are the symptoms for malignant pheochromocytoma
high blood pressure
headaches
sweating
forceful palaptations
temor
facial pallor
MP, NETS have:
specific receptors at membrane
specialist neuroamine uptake mechanisms
In the adrenal medulla, some cells produce catecholamines. MIBG concentrates in the secretory granulose of the cells. Tumours which produce catecholamines are eager to metabolise this
High doses of I-131, MIBG are used
what does PRRT used
radioactive labelled analogue therapy
what is the physiology of the RSAT
somatostatin is a hormone in the body, which binds to receptors which slows down hormone production, controls gastric and bowel emptying
if there is an abnormal increase treatment might be suitable
must be symptomatic with unresectable or met progressive disease
what is the treatment for PRRT
as some NETS overexposes surface receptors, the somatostatin analogue is taken, the radionuclide with a beta radionuclide. A therapeutic dose must be delivered to the tumour
Yttitrium-90 and Lu-177 most common
what does SIRT stand for
selective internal radiation therapy
SIRT
for primary and secondary inoperable tumours in the liver
last resort
normal liver draws 80% of blood from portal vein
tumours draw more than 80% of their blood from the hepatic artery
what is TARE
Trans-arterial Radioemoblisation
who is TARE for
functioning live with a primary unresectable tumour, HCC
not suitable for TACE
secondary liver tumour with colorectal injury
options discussed in MDT
selected by hepatobillary cancer MDT
what happens during the planning angiogram for SIRT
takes 1-2hours
identify blood supply to the liver
local anaesthetic
contrast injected
small blood vessels are blocked so the microspheres can be located
150MBq radioactive tracer [Tc-99] injected into the catheter
SPECT-CT picks up the radioactive tracer, locating the liver
recover overnight in hospital
what happens after the planning angiogram
1-2 weeks after it is repeated
when the catheter is in the liver the microspheres are injected in which takes approx 1 hour
catheter is removed and wound is dressed
pain meds and antiemetics
scan checks the beads
what are the SE for SIRT
nausea
abdominal discomfort
chills
raised temp
stomach pain
diarrhoea
fatigue
cholecystitis: pain, nausea, fever
microspheres in lung = cough and SOB
microspheres in GI tract = nausea, pain, pancreatitis, stomach ulcer and bleeding
hazards with SIRT
wash hands thoroughly
avoid contact with pregnant women and children for the first week after
sleep alone for first 1-2 nights
microspheres remain in the liver
CT scan 2-3 months post treatment
regular liver and kidney tests
what is refractory myeloproliferative disease/ PRV
over production of RBC, uncommon in bone marrow
what are the symptoms of PRV
hyper viscosity
headaches
dysponea
blurred vision
sweating
weightloss
2/3 have enlarged spleen
pruritis
flushed complexion
anaemia due to poor flow
where is PRV seen
50-60
male
main cause of death is haemorrhage, or thrombosis, due to increased blood flow
raised RBC increases WBC and platelets
median survival: 9-13 years
if not treated 50% die within 18 months
what is the treatment for PRV
venesection: one pint of blood is taken at regular intervals, repeated at 24 hours and then 48 until packed cell volume <0.5 [temporary solution]
Chemo- chlorambucil or busulphan (every 4-6 weeks)
P32: sodium phosphate
describe P-32 as a treatment option
neutron irradiation of P-31
half life = 14.3 days
emits beta particle: 3-8mm range
decays to non radioactive sulphur
usual dose = 150-250MBq
initial dose = 74-111 MBq
further treatments = max 260MBq
where is there rapid uptake of P-32
in rapidly dividing cells
it is selectively uptakes into haemopietic tissue
it is incorporated into DNA of rapidly dividing cells
what does P-32 inhibit
marrow, therefore blood production
highest conc is in bone marrow and trabecular
administration of P-32
oral or IV
syringe has perspex casing for shielding
20 minutes through butterfly to avoid extravasations
check circulation
average response time is 7 days
administrator must wear film badge, gloves, mask etc
caution with taking a blood sample as it will be radioactive
effective dose is 465mSv
what are the hazards of P-32 sodium phosphate
long term will cause leukaemia in 10-15%
GI absorption causes symptoms similar to irritable bowel
don’t give to pregnant, breast feeding women and children
clinical applications for unsealed sources
orally via capsule
radioactive gas
IV
nuclear med
diagnostic imaging: diagnosis or localisation
in vivo studies: patient injected with radioactivity samples taken to measure the level in blood, urine and faeces
in vitro: in glass, radioactivity is injected into blood, faeces and urine outside the body i.e radioimmunoassay uses antibodies to detect and quantitate the amount of an antigen
treatment: molecular RT or radio-immunotherapy
how is a tumour localised
- a pharmaceutical is elected which will seek out the tumour
- label the pharamacuetical use a radionuclide which won’t interfere with the uptake of the pharmaceutical but allows for easy detection
- detects the pattern of distribution of gamma rays emitted by the radiopharmaceutical with a gamma emitter
- use the smallest activity practicable to minimise hazard, as staff will be irradiated
advantages with localising
looks at function and position
disadvantages with localising the tumour
limited to small masses <10mm in diameter, if larger multiple treatments might be needed
location is hard to define
diagnostic: gastric
looks at motion of food through the oesophagus into the stomach and its transit time
water, eggs, toast and Tc-99M
ant and post dynamic images at regular intervals for up to 4 hours (stomach emptying takes 3/4 hours)
draws ROI around stomach, GI tract and creates decay corrected curves for activity
diagnostic: gall bladder ejection function
Tc-99m hydroxy iminodiacetic acid
after excretion by the liver into bile which travels through the gall bladder + bile duct
GB contrast and empties due to the cholecystokinin injection
images are taken at intervals
IN VIVO
CR51 EDTA = radioactive substance
doesn’t break down by body components/processes
GFR is recorded to indicate whether the kidneys can filter and process chemo so won’t experience renal failure
a curve is plotted for GFR
allows the function to be visible rather than the anatomical definition it detects issues early
principles of radionuclide therapy
RP are chosen for their selective uptake
doses are delivered internally via physiological processes
aim: deliver high doses to specific organs and tissues to deliver sufficient dose internally but spare normal tissue, resulting in cell damage
what is the radionuclide criteria
physical properties: sufficient dose to TV
type and energy of radiation emitted
range of emission
physical half life
chemical characteristics:
viability of tumour cell
radiosensitivty
proliferation rate
specificity of targeting - preferential uptake
binding to the radioactive label to pharmaceutical
effective half life
what cells are radiosensitive
spermatogonia
erthyroblasts
lymphocytes
what cells are radioresistant
muscle cells
neural cells
what is T-90 used for
treating benign tumours
what increases biological effectiveness
high dose rate
what rate does radionuclide therapy have
variable
the initial dose rapidly decreases due to physical decay and biological clearance
LET
the amount of energy deposited for a given distance by a particle moving through an absorber
low dose =
low LET = SSB
high LET =
DSB
how much greater is alpha LET to beta
10-1000x
I-131
decays by beta particle emission
cheap and accessible
readily attaches to the MIBG pharmaceutical to form a stable, non toxic radiopharmaceutical, remains couples to the radionuclide and is not metabolised.
cells local to the site of despot achieve a higher dose so normal tissue is spared
prep for I-131
stop any drugs which might interfere
scan first = iodine -123m MIBG
block thyroid with potassium iodate at least three days prior continue for a period after treatment
improve hydration
consent
blood test
pregnancy test
antiemetics
procedure for I-131
6000-8000MBq via IV
isolated unit
infusion takes 2 hours
monitor signs
drink plenty
1-5 doses administered at 3-6 month intervals
hazards with I-131
remain in isolation for 4-7 days, to get to safe level
visiting restrictions
non children, breastfeeding or pregnant women
scanned before uptake
liver receives highest dose
avoid getting pregnant for the first 6 months or fathering a children for 4 months
nausea and vomiting first 2 days
bone marrow suppression (4-6 weeks)
hypothyroidism may occur
beta particle emitter
different range of energies, variable speed and ranges
must match what is needed
tumour size is important with the range
why is a medium range good
great therapeutic effect, delivers dose to the target, but can have less dose homogeneity to the tissue due to gaps in the tissue
higher dose =
high homogenous dose to large target
when should a long range not be used
if near healthy tissue
what should be considered when selecting a emitter for therapeutic effect
effective range
relative biological effectiveness to tumour mass
size
radiosensitivity
homogeneity
what are the ideal therapeutic properties
high localised dose to TV
minimal uptake to distant tissues
remain attaches to parent carrier drug and excreted by a simple route
half life long enough to accumulate in TV for effective treatment but short enough to avoid non beneficial radiation dose
phosphorous - 32
high local dose
long range
no gamma rays
P-31 (n, gamma) -> P-32
neutron bombardment, making it more unstable so it is radioactive
ideal §
Yttritium-90
high beta emitter
64 hour half life
0.94 MeV
3.6mm range
can affect tumour cells up to 11mm length in soft tissue
Iodine-131
emits a low beta particle
only for small tumours
364 and 606 KeV energy
gamma ray emitted so significant irradiation to surrounding tissues
what is planned during radiation uptake
the organ which will receive the uptake, so that it complies
the dose received from the RP depends on amount of energy deposited by the radiation.
what is the cumulative activity dependent on
radiopharmaceutical, the patient and the half life
what must be known
the targeting organs, uptake and clearance
absorbed dose depends on…
organ involvement, distance apart, how long it remains in the blood stream and the individual
dose equivalent =
absorbed dose X factor
takes into account the energy distribution in the tissues
1Gy of alpha is more harmful than 1Gy of beta
what does dose equivalent enable
comparison of all ionising radiations regarding the potential cause of harm
what have a factor of 1
gamma, x-rays and beta
what is the factor for alpha particles
20
what LET does alpha have
high, so effective but needs to be bonded to the cell due to the short range
alpha emitter
hard to dispose safely
pure emitters don’t have an external hazard risk
negative effects: cancer induction, genetic diseases, congenital malformations and degenerative changes
what are the target tissues for alpha
respiratory tract, bone, liver, reticuloendothelial
what treats hormone relapsed prostate cancer with bone mets
Ra-223 dichloride
delivers alpha radiation without affecting normal bone marrow
I-131
half life: 8 days
beta kev: 182
range: 3mm max
gamma kev: 364, 606
uses: thyrotoxicosis
T-90
half life: 2.7 days
beta kev: 935
range: 3.6mm avg
gamma kev: -
uses: arthritis, functioning NET
P-32
half life: 14.3 days
beta kev: 695
range: 8mm max
gamma kev: -
uses: PRV
Lu-177
half life: 6.6 days
beta kev: 497
range: 1.7mm max
gamma kev: 208 max
uses: functioning NETs, advanced prostate cancer
Sr-89
half life: 50-55 days
beta kev: 580
range: 2.4mm avg
gamma kev: 909
uses: bone mets
Sm- 153
half life: 1.9 days
beta kev: 220
range: 0.6mm avg
gamma kev: 103
uses: bone mets
Ra-223
half life: 11.4 days
alpha 5-7.5 MeV
range: <1mm
gamma kev: -
uses: bone mets CRPC
