Radiopharmacy Flashcards
what is nuclear medicine?
scans that give poor anatomical detail but do show functionality of the organs
what are radiopharmaceuticals made out of?
‘useful molecule’ that allows us to target desired organ
+
radioactive isotope that acts as tag for detection on imaging
Does nuclear medicine show anatomy or function?
function
Do XRAYS and CT show good anatomical detail or good indication of function?
anatomical detail/ anatomy
briefly describe how a gamma camera works? and outcome?
px given radioopharmaceutical + gamma photons detected by detector camera… gives pic of organ
why/how are only gamma photons detected by detector?
as dont interact with tissue= dont directly damage px, but are detected
whats a collimator? what does it detect/not detect?
sheet of lead with holes to allow certain gamma emissions to come out + be detected by detector of gamma camera,
so those at angle arent detected and plotted
what is the measurements used for radiation energy in tissue?
sievert (Sv)
how much is mSv?
1/1000
how much is a microSv?
1/1 000 000
how much bits of energy absorbed is NOT JUST influenced by how radioactive it is, but also by what else?
(what 2 factors affect Sv?)
how its been shielded (lead thickness)
how been stored
effect of shielding/ not shielded vial of radiation, on your abdorbed radiation dose after you sit next to it.
provided same amount of radioactivity in vial?
no shield: your absorbed radiation dose (sc/msv) increase
shield: amount of energy px absorbs lower (msv exposed to)
2 points to philosophy of radiation protection?
- all exposures shall be justified (benefit > risk)
- all exposures shall be kept ALARP
why is ALARP important?
as it means that the radiation given to a px is AS LOW AS REASONABLY POSSIBLE
4 sources of radiation that humans are exposed to in small amounts?
cosmic radiation, radon gas, buildings and food
average natural radiations for UK per year?
2.5mSv. but will inc if have scan etc
why does the soil in cornwall give off the most radon? thus inc mSv?
has the most granite which gives off radon gas
highest radiation workers?
airline staff
several mSv per year
what are effects of long exposure of radiation?
effects the bone marrow
skin reddening / burning
pelvis radiotherapy = diarrhoea
neck radiotherapy = vocal chord damage
what is the main concern of radiation?
carcinogenesis
(normal cells-> cancer cells)
assume risk whatever the dose
what is the radiation risk for 2mSv exposure of harm?
1 in 15 000
what is the inverse square rule?
strength of the X-ray beam is inversely proportional to the square of distance from the source (X)
i.e.
if you decrease the distance from radioactive source by 1 the area of exposure increases by 4
how to reduce and limit radiation exposure?
time
distance
shielding
… sops, staff training, monitoring and feedback
L2:
diagnostic use of radiopharmaceuticals? to get info on …
struc, function or degree of involvement with a disease process of organ/ body tissue
why might patients with breast or prostate cancer have radiopharmaceutical bone scans?
see if it is spread and there are bone lesions
why might the bladder come up as dark under gamma cameras?
radioactive substance in excess will go to bladder as it is excreted in the urine
how can low radiation dose be maintained for patients? 3 idealistic PK of radiopharmaceuticals
- use radionuclide with short physical half life
- short biological half life
-nature of radioactive decay
what’s the difference between physical and biological Half life?
physical- time to reduce radioactivity level to 1/2 original value due to radioactive decay.
biological- time for biological system to eliminate 1/2 of substance (such as a radioactive material) that has entered it.
how long should a radionuclide usually hang around for in the body?
2-3 hrs
which unit of radiation relates the rate of disintegration but does not tell you anything about the radiation dose to px/ workers?
becquerel
how many becquerels is equivalent to 1 distintegration per second?
1 d.p.s
why do nuclei disintegrate?
nuclei unstable, want become stable by disintegrating + getting rid of energy as gamma photons/a/b parts.
each time it disintegrates = 1dps = 1 becquerel
what do radioactive substances release in order to remain stable? 3 types of radioactive decay
gamma photons or alpha and beta particles
are beta and alpha particles useful for diagnostic imaging, yes or no?
no
if you have a vial of radioactive substance, what happens to the becquerels and sieverts if you place it in an appropriately lined lead container?
b stay the same and s decrease
alpha particles are essentially He nuclei with a +2 charge. Why are they not suitable for diagnostic testing in the body? 3
large, collide with tissue (dont go straight through) and give up energy, considerable damage in small area
alpha particles can be shielded easily but cause lots of damage if ingested or touch skin , true or false?
true, so must wear gloves
beta particles have a negative or positive charge and are smaller than alpha particles so have less damage and interaction with tissue. Why can they therefore not be used for diagnosis?
still interact with tissue and cause some damage
what does range (of several cm) of b particles depend on?
energy Emax and Emean
B+ particles aka positrons - antimatter interact with what and when?
b- particle immediately after emission form nucleus
Annihilation reaction: matter -> pure energy with 2 gamma photons emitted.
b+ + b- –> what? in an annihilation reaction
2y (gamma photons)
B+ particles aka positrons - antimatter - valuable in diagnostic procedures, yes or no?
yes
are gamma rays electromagnetic (EM) radiation or particulate?
EM radiation
why are gamma rays more suitable to be used in tissue?
less interaction, cause less damage and have greater range .. in tissue
valuable for diagnostic
is the energy of emitted gamma rays constant or variable for a given nucleotide?
constant
what are the 9 ideal diagnostic properties?
- gamma ray emission only
- for imaging studies, 100-250 Kev
- physical half life of approx. 1.5x(test duration)
- simple cheap, rapid production
- versatile chemistry
- chemical quantity
- radiochemically pure sample
- chemically stable
- predictable biodistribution
for diagnostics,
want gamma ray remission only in X abundance, and to Y radiation dose to px
high
reduce
for diagnostics: imaging studies, want gamma energy of 100-250kev. 3 reasons why?
high detection efficiency,
no significant body attenuation
easy to shield
what can be done to reduce body attenuation in overweight patients to obtain good imaging?
inject more radioactivity into them
physical half life of diagnostic radionuclide should be approx how many times the duration of the test?
1.5
for dianostics, want simple cheap and rapid production, why?
to reduce handling time and exposure.
- lack of radionuclidic impurities
- high specific activity (conc.ed)
- rapid prodn reduces operator dose
? for diagnostics, why do you want radiochemically pure radiopharmaceutical? (biodistribution profile)
radiopharm. made is mostly bound to ligand. = most of uptake in organ you want + not impurity = gets taken up elsewhere, doesnt contribute to pics
for diagnostics, why do you want predictable biodistribution?
so from pics you can tell whats normal/not
Technetium 99m (Tc) is a manufactured element with an atomic number of 43 and has 20 different isotopes, which are all…
radioactive with t1/2 of few secs - millions of years
what is the half life of Tc 99m?
and y energy?
6 hrs
140keV
explain what is meant by meta stable?
e held further from nucleus and energy being used to hold, spontaneously it drops down closer to nuc and energy emitted by nuc as a gamma photon
what does Tc decay to?
Ru 99
see Tc-99m diagrams p37,38
whats emitted in 99Mo -> 99Tcm reaction/ what does 99Mo split into?
b- and y
2) whats emitted in 99Tcm -> 99Tc reaction?
y
3) whats emitted in 99Tc -> 99Ru reaction?
b-
why dont we give 99Mo to patient? and how will it be changed to be able to be given?
high energy-> very high radiation dose :(
would have to react and change to 99Tcm -> 99Tc -> 99Ru
why can Molybdenum and Technitium (Mo and Tc) be separated?
they have different chemical properties
what is the source of 99Mo?
from fission of U-235 in nuclear reactor
U-235 bombarded with thermal neutrons
nuc splits -> 2 daughter nuclei
large range of nuclides produces
Mo99 can be separated rel. easily
how does a technetium generator work?
how is Tc99m obtained?
shielded glass column packed with alumina, Mo99 in solid form (molybdate) is strongly adsorbed onto column
column sealed, sterilised, packed into generator
depatched to hospital radiopharm dept
Mo99 on column decays to Tc99m, which is separated
how is Tc-99m separated from Mo-99 in Tc generator?
saline passed through column, Tc is soluble so left with radioactive solution
What happens on an Mo column to get 99mTc
99Mo (some) spontaneously decays -> 99mTc. after saline passed through to separate.
how long does it take for a technetium generator to re-establish an equilibrium? (graph p 47)
22.89hrs (to get almost all Tc in there out)
check back once a day.
Tc drops, then inc again, both Tc and Mo dec over time
the chemical form of Mo is Molybdate, MoO4-, which decays to form what?
pertechnetate TcO4-
what process elutes pertechnetate TcO4-? (and eqn + name of reaction?)
passage of saline through alumina
Na+Cl- + TcO4- = Na+TcO4- + Cl-
ion exchange
sodium pertechnetate is used for how many days?
1
what is the term given to the ratio expressed as a % of the radionucelide concerned when compared to the total radioactivity of the source?
radionuclidic purity
Mo can get through the thickness of lead therefore any detection of radioactivity outside of the shield can be attributed to this, true or false?
true
if mo is low on first elution you can be confident that generator is suitable for use, true or false?
true
99Tc/99Mo generator radionuclidic purity identification not done routinely, but can identify what?
unknown isotopes (e.g. if have a spill)
can be useful with unlicensed material
3 methods to identify radionuclidic purity
- molybdenum breakthrough test
- gamma spectroscopy (measure energies emitted)
- measure decayed sample (determine half life)
give 4 things that choice of generator is based on?
ease of operation, efficiency + safety profile and cost
what grade of environment should elution happen in?
A
should the collection vial reach atmospheric pressure before or after removal? and why?
before to prevent aerosol production
generator: whats required to protect operator?
shielding
as Mo has high radiation
sodium pertechnetate can be administered directly in that form and is most commonly used for what indication?
thyroid imaging
why is pertechnetate taken up by thyroid?
similar in size and charge to chloride and iodide ions, thyroid mistakes it for iodide and uptake happens
sodium (99mTc) pertechnetate is more commonly manipulated to make Tc in diff chemical form, why?
diff chemistry = diff biodistribution
get info from different parts of body
TcO4 - chemically stable and Tc has a valency of +7. in order to make Tc react, what must be altered? and how/why can this be done?
valency state of Tc.
has partically filled N and O orbitals (?) as has 43 e- (atomic no).
Tc can exist in valency states of +7 to -1 and form range of coordination complexes
L3.
99m TC is eluted in most stable ox state (+7) and surrounded by big oxygens therefore ligand cant near it. How is it made more reactive in kits?
kits have tin ions which are more reactive, bind with oxygens and leave tc highly reactive, to attach to ligand / water to give Tc colloid
what is most frequently used in kits as a reducing agent?
stannous chloride (Sn++)
how are Tc radiopharmaceuticals prepared?
simple, usually single addition of TcO4- to kit - freeze dired vial
draw up eluent
dilute it
add to kit
wait 10/15 mins
complex forms
are most kits single or multi dose?
multi dose containers
all Tc prep manipulations are performed aseptically true or false?
true
NEVER inject air into any Tc radiopharm. vial.
what is one consequence of injecting even 0.1ml of air into a technetium vial?
can oxidise stannous ion used as a reducing agent
why do vials contain nitrogen atomosphere?
prevent oxidation of tin Sn++ stannous chloride
radiopharm kits contain all the required ingredients for prep of Tc radiopharms such as? lsbs
ligand
Sn++
buffers
stabilisers
radiopharm kits are amde into a…
single, sterile freeze dried rubber capped vial
how does addition of TcO4 into kit cause chem reaction?
it dissolves freeze dried powder to -> reaction
why is choice of ligand in Tc radiopharm prep important?
structure of Tc-ligand determines biodistribution (in px)