Radiopharmaceuticals Flashcards
(164 cards)
1
Q
X-rays give a good image of anatomy but a poor image of that?
A
Function.
2
Q
Nuclear medicine scans give a good image of function but a poor image of what?
A
Anatomy.
3
Q
What is a gamma camera?
A
This is the piece of technology used to image the radiation given off by the radioisotopes used in nuclear medicine imaging.
4
Q
The philosophy of radiation protection follows which two basic tenants?
A
• All exposures shall be justified.
o The benefit gained outweighs the risk involved.
• All exposures shall be kept as low as reasonably practicable (ALARP).
5
Q
We are constantly being exposed to radiation. Give some sources.
A
Radiation comes from cosmic radiation, radon gas coming from the ground, buildings, and foodstuffs to name a few.
6
Q
What is a Sievert (Sv)?
A
This is the unit used to measure radiation energy in the tissue. Sievert is the unit quoted when looking at rules governing exposure.
7
Q
What is the average radiation exposure for a member of the public in Sievert?
A
The average exposure for a member of the general public in the UK is 2.5 mSv per year.
8
Q
In practice, what is the range of energy used, measured in sievert?
A
In practice, the levels of energy used, measured in Sievert, are often in the range of milliSievert (mSv) or microSievert (µSv).
9
Q
How can sievert be calculated?
A
Sievert can be calculated by multiplying Gray by the quality factor (QF). For beta and gamma emitters, the quality factor is one.
10
Q
Define the unit Gray (Gy).
A
This is the S.I. unit of absorbed radiation dose. It is one joule of energy absorbed per kg tissue.
11
Q
Define the unit Bequerel.
A
This is the rate of degradation of radioisotopes (1 nucleus d.p.s). This unit or radiation measure says nothing about the radiation dose that patients or workers are exposed to, however.
12
Q
In the US the equivalent of the Becquerel (Bq) is the Curie, what is one millicurie equivalent to?
A
In the US this unit is the Curie, with one millicurie being equivalent to 37MBq.
13
Q
What is the main concern with radiation exposure?
A
The main concern with radiation exposure is carcinogenesis (formation of cancerous tumours).
14
Q
What is the general rule of thumb when it comes to the effects of radiation exposure?
A
The general rule of thumb is that one should assume a risk, whatever the dose of radiation may be.
15
Q
What is the risk of having serious side effects from exposure to a radiation dose of 2mSv?
A
1 in 15,000.
16
Q
How can radiation exposure be limited?
A
- Increasing the distance between the radioisotope and the operator.
- Reducing the length of time that the operator/patient is exposed to radiation.
- Using shielding (usually lead).
17
Q
In an effort to reduce radiation exposure, what must SOPs include?
A
- Staff training.
- Monitoring.
- Feedback (usually monthly).
18
Q
Describe alpha particles.
A
These are He nuclei, with a charge of +2. They are comparatively large so collide with tissue, giving up their energy, and cause ion pairs. This leads to considerable damage in a small area.
Their range through tissue is a few mm. They can be easily shielded as they are ‘big’ molecules.
These particles have no use as diagnostic agents however they can be used as therapeutic agents (e.g. Ra-223).
19
Q
What two types of beta particles are there?
A
Negative and positive beta particles.
20
Q
Describe negative beta particles.
A
These are smaller than alpha particles so have less interactions with tissues (50 ion pairs per cm). Because they are smaller, they also have a greater range of penetration in tissues; this range can be up to several cm depending on energy max and energy mean.
These particles are also not used for diagnosis but are valuable for therapy.
21
Q
Describe positive beta particles.
A
These are also known as positrons or antimatter. Immediately after emission from a nucleus, they collide with a negative beta particle. This leads to an annihilation reaction where matter is converted into energy (2 gamma particles/waves are formed).
22
Q
Describe gamma rays.
A
Gamma rays are a form of electromagnetic radiation, not particles. They have less interaction with tissue so cause less damage and have a greater penetrative range in tissues.
The energy is emitted gamma rays is constant for a given radionuclide. They are valuable for diagnostic use, especially when radiation can be detected externally.
23
Q
Describe the ideal properties for diagnostic radionuclides.
A
• Gamma ray emission only. o High abundance. o Reduced radiation dose to the patient. • For imaging studies, gamma energy 100 - 250 keV. o High detection efficiency. o No significant body attenuation. o Easy to shield. • Physical half-life approx. 1.5 times duration of test. • Simple, cheap and rapid production o Lack of radionuclidic impurities. o High specific activity. o Rapid production reduces operator dose. • Versatile chemistry. o To allow a range of labelling applications. • Chemical quantity – no pharmacological effect. • Radiochemically pure. o Biodistribution profile. o So only one energy is emitted. • Chemically stable. o Doesn’t break down in vivo. • Predictable biodistribution.
24
Q
What is the most commonly used radioisotope for diagnostic radiopharmacy?
A
Technetium 99m.
25
How many different isotopes of technetium are there?
20.
26
What is the energy of the gamma ray emitted when 99Tcm degrades to 99Tc?
140 keV.
27
What is the half-life of technetium 99m?
6 hours.
28
What makes molybdenum and technetium seperatable?
Different physiochemical properties.
29
Where is the Mo99 used in Tc99 generators derived from?
The fission of U-235 in nuclear reactors.
30
Where are the main sites for Mo99 production found? Are there any sites in the UK?
The main sites for the production of Mo-99 are in Holland and South Africa, there are none in the UK.
31
Explain the technetium generator and how it is used.
This device contains a shielded glass column packed with alumna, to which Mo-99 (as its chemical form molybdate MoO4--) is strongly adsorbed.
This molybdate slowly decays to produce pertechnetate (TcO4-). Passage of saline through the alumina elutes pertechnetate and the sodium pertechnetate is used for one day.
32
How many Tc generators may be received by a site each week?
2.
33
What factors are taken into account when it comes to the choice of Tc generator?
This is based upon ease of operation, efficiency, safety profile, and cost.
34
List some practical points for the use of a Tc generator.
* Must swab collection vial’s rubber bung.
* Should elute in a grade A environment.
* Make sure collection vial has reached atmospheric pressure before removal - try to prevent aerosol production.
* Require shielding to protect the operator.
35
Can sodium pertechnetate be administered directly in this form?
Yes.
36
What is the most common indication for sodium pertechnetate?
Its most common indication is thyroid imaging; this is because it is preferentially taken up by the thyroid as molecules of sodium pertechnetate have a similar size and shape to iodide.
37
What can different chemistry of Tc lead to?
Different chemistry leads to different biodistribution so one can get different information from different parts of the body.
38
Pertechnetate is chemically stable, with Tc having a valency of +7. In order to make it react, what is needed?
One needs to alter the valency state of Tc. Oxidation states of -1 to +7 are known.
39
How does the BP define radionuclide purity?
‘The ratio, expressed as a percentage, of the radioactivity of the radionuclide concerned to the total radioactivity of the source’
40
What methods can be used to test the purity/identity of nuclides in the Tc generator?
* Molybdenum Breakthrough Test.
* Gamma Spectroscopy.
* Measurement of energies emitted.
* Measurement of the decayed sample.
* Determination of half-life.
41
Why is it hard to bind ligands to pertechnetate?
Here, all 7 electrons are shared with 4 oxygens; these oxygens are ‘big’, so a ligand is unable to get near to the Tc to bind.
42
Explain how tin ions in a radiopharmaceutical kit are used.
Tin ions in the kit are more reactive to oxygens, which take them from the TC, leaving it highly reactive (reduction). In this state one can attach to a ligand or the Tc may react with water to give Tc-colloid which is an impurity.
43
To prevent the Tc from reacting with oxygen in the air and reverting to pertechnetate, what is used?
Nitrogen-rich vials.
44
Outline the simple technique for the preparation of Tc radiopharmaceuticals?
The simple technique for preparation of Tc radiopharmaceuticals usually involves single addition of TcO4- to a kit which is a freeze-dried rubber capped vial containing all the required components. Addition of TcO4 dissolves the freeze-dried powder and a chemical reaction occurs.
45
What do simple Tc radiopharmaceutical kits include?
This includes ligand, reducing agent, buffers and stabilisers. In these kits, the most frequently used reducing agent is stannous chloride.
46
All manipulations of Tc radiopharmaceutical kits must be performed how?
Aseptically.
47
Why should preparation of radiopharmaceutical kits be kept as simple as possible?
Preparation should be kept as simple as possible so there is a little handling as possible leading to lower radiation exposure to staff and less change of microbial contamination.
48
To image the bones, what ligand is used?
To image bones, the methylene diphosphonate (medronate, MDP) ligand is used.
49
How does the MDP ligand work to image bones?
This ligand binds to hydroxyapatite Ca10(PO4)6(OH)2 therefor the greater the bone turnover, the greater the uptake of the ligand. Hence, it shows osteoblast activity.
This can detect changes before there are any changes in bone density.
50
What methods are used to assess radionuclide purity?
Column chromatography (HPLC) and planar chromatography.
51
What should the percentage of Tc-ligand be to pass quality control?
>90%.
52
What should the percentage of free TcO4 and reduced Tc be to pass quality control?
<5%.
53
Which mobile phases are used for planar chromatography used to assess the purity of radionuclides?
* Butanone or acetone may be used to separate 99mTcO4 from the mixture.
* Saline used to separated 99mTcO4 and 99mTc-ligand from 99mTc-colloid.
54
Wy is QC needed with Tc radiopharmaceuticals?
Free TcO4- will be taken up in salivary glands, thyroid, and stomach. Reduced Tc goes to
liver and spleen - i.e. irradiation of unintended organs. This can also lead to sub-diagnostic images and possibly the need for more scans, increasing radiation dose.
55
What is lung perfusion imaging performed by?
Lung perfusion imaging is performed by IV injection of 99mTc MAA (macroaggregates of albumin - typically 30-50µm).
56
How does 99mTc MAA work?
These particles lodge in the terminal arterial-capillary bed of the lungs and this assesses blood supply.
57
Areas which show increased uptake of 99mTc MAA in lung perfusion imaging could be caused by?
* PE.
* Inflammation.
* Neoplasm.
* COPD.
58
Which other lung test is carried out at the same time as lung perfusion imaging?
Lung ventilation is also carried out in conjunction with perfusion.
59
Which radioisotope is often used for lung ventilation imaging?
81mKr.
60
Where does the 81mKr used in lung ventilation imaging come from?
This comes from a patient side generator from which the patient breathes to visualise the ventilation of the lungs. These generators have to be ordered in each day.
61
What alternative is there for 81mKr for lung ventilation imaging?
99mTc Technegas, which is expensive to buy but cheap to run.
62
If both the lung perfusion and ventilation imaging tests are done at the same time, what must be ensured?
That different isotopes are used to the two images can be differentiated.
63
Patchy uptake on perfusion and normal ventilation can be indicative of what?
PE.
64
What is the acquisition time for a lung scan?
20 mins.
65
What is the most common indication for a bone scan?
A most common indication for a bone scan is to assess bone metastases that are usually secondary to breast and prostate cancers.
66
As well as being used to assess bone metastasis, what else can bone scans be used for?
The bone scan also used for diagnosis of Paget's, osteomyelitis and stress fractures (often associated with sport).
67
What agent is used for a bone scan?
Medronate or oxidronate (500mBq).
68
How long after injecting the imaging agent is the scan carried out?
2-3 hours later.
69
Where is enhanced uptake seen in a bone scan?
Uptake is enhanced in active areas of bone growth and abnormal uptake is seen as hot spots.
70
How long is the acquisition time for a bone scan?
30 mins.
71
Nice guidelines 2003 state that MPI (myocardial perfusion imaging) scintigraphy using SPECT is recommended for use in what?
Diagnosis and management of coronary artery disease.
72
Patients undergo MPI in two parts, what are they?
* Heart stressed by exercise or pharmacologically using adenosine or dobutamine.
* Heart imaged at rest.
73
What does a MUGA scan provide information on?
Left ventricular ejection fraction.
74
For a 3D tomographic heart scan for ischaemia (poor blood supply to the heart muscle), what agent is used?
600 MBq of Tc99m-Tetrofosmin.
75
Where does the Tc99m-Tetrofosmin used in a 3D tomographic scan for ischaemia tend to bin?
The mitochondria in heart muscle.
76
How does a planar heart scan to assess LVEF work?
Stannous agent (tin) is injected into the blood. 800MBq od Tc99m-O4 is injected and this sticks to the stannous agent, labelling the blood. The scan is taken straight away.
77
What is the acquisition time for a planar heart scan to assess LVEF?
30 mins.
78
What was the first radiopharmaceutical, and the gold standard, for imaging cerebral blood flow imaging?
The first radiopharmaceutical was HMPAO Ceretec and this became the gold standard for cerebral blood flow imaging.
79
What agent is used to differentiate essential tremor from parkinsonian syndrome in patients with an unclear diagnosis?
123Ioflupane DaTSCAN is used to differentiate essential tremor from Parkinsonian syndrome in patients where diagnosis is uncertain.
80
Where does 123Ioflupane (DaTSCAN) accumulate in the brain?
In the striata of the brain, used to coordinate movement.
81
How long after the agent is injected in a DaTSCAN brain scan can the scan be done?
3 hours.
82
How long is the acquisition time for a DaTSCAN brain scan?
30 mins.
83
Why might some patients find the DaTSCAN brains can uncomfortable?
It can be quite claustrophobic when the scan is taking place.
84
What can nuclear medicine be used to image in the GIT?
* Salivary activity and secretion can be monitored using pertechnetate.
* Tc-colloid mixed with food or drink used for gastric emptying studies – pancake or scrambled egg.
* Oesophageal transit measured using Tc-colloid in tomato soup.
* GI bleeding assessed using Tc labelled RBC.
85
Nuclear medicine scans of the liver have declined as which scanning methods have increased in use?
Ultrasound and CT scans.
86
What are the three main types of renal nuclear medicine imaging?
* Study of GFR using 51Cr EDTA.
* Renal perfusion using MAG 3.
* Renal parenchymal function using DMSA.
87
With the addition of furosemide or captopril, renal scans can be used to assess what?
They can be used to identify renal vascular hypertension and renal obstruction.
88
What can white blood cells be labelled with?
White blood cells can be labelled using 99mTc or 111In.
89
Following reinjection, where do labelled RBCs migrate to?
Following re-injection WBC migrate to sites of infection and inflammation. This can be useful for diagnosis of infection of unknown origin.
90
Nanocolloid in sentinel node imaging can be used for which cancers? Why is this useful?
Nanocolloid in sentinel node imaging can be used in breast cancer and melanoma. This allows one to see the nodes which need removing instead of removing them all.
91
What is octreoscan used for?
Octreoscan used in somatostatin receptor tumours e.g. carcinoid.
92
What is FDG-PET scan used for?
FDG-PET scan used in lung cancer.
93
What does knowledge of radiopharmaceutical interactions rely on?
Knowledge of radiopharmaceutical interactions requires/relies on reporting, however, the number of reports made is small.
94
Into what four categories can radiopharmaceutical interactions be classified?
* Unusual handling of the radiopharmaceutical as a result of the pharmacological effect.
* In-vitro physiochemical interaction between the radiopharmaceutical and the patient’s medication.
* A drug-induced disease affecting the transport of radiopharmaceuticals.
* Drugs which interfere with the radiolabelling of white cells.
95
Define unusual handling of the radiopharmaceutical as a result of the pharmacological effect.
“A pharmacological interaction occurs when the intended effect of a drug at its usual dose alters the biodistribution of the radiopharmaceutical” This is where the pharmacological effect of a drug causes the organ to function differently.
96
WHich type of radiopharmaceutical interaction is the most common and makes up the largest proportion of reports?
Unusual handling of the radiopharmaceutical as a result of the pharmacological effect.
97
What drugs can interact with hepatobiliary imaging agents?
Opioid analgesics, enzyme inducers (e.g. phenobarbitones), anaesthetics.
98
How is hepatobiliary function investigated?
Hepatobiliary function is investigated using 99mTc labelled compounds of iminodiacetic acid (IDA) (e.g. mebrofenin). This is cleared from the circulation by the hepatic cells and secreted like bilirubin into the bile carrier mechanism.
99
How can opioid analgesics interact with hepatobiliary imaging agents?
Cause constriction of the sphincter of Oddi increasing pressure in the common bile duct; could increase the transit time of the radiopharmaceutical. (Class-specific).
100
How can enzyme inducers (e.g. phenobarbitone) interact with hepatobiliary imaging agents?
Enhance and accelerate biliary excretion of RP increasing accurate differentiation between extrahepatic biliary atresia and neonatal hepatitis. (Class-specific).
101
How can anaesthetics interact with hepatobiliary imaging agents?
Halothane has been shown to cause a marked decrease in hepatic blood flow, causing reduced uptake of RP in the liver. (Drug-specific).
102
Intense renal uptake of 99mTc PYP (blood pool imaging) was seen when what class of drugs were used at the same time as the imaging?
Cytotoxic drugs.
103
Intense renal uptake was seen when cytotoxic drugs were used in combination with 99mTc PYP (blood pool imaging). What was the suggested reason for this?
It was suggested that this was due to altered renal tubular function or reduced GFR. (Class-specific).
104
Which drugs may interfere with the uptake of tracer in thyroid scans, leading to a possible misdiagnosis?
Any drug which interferes with the uptake of iodine or blocks its release from the thyroid.
105
Give specific examples of drugs which can affect thyroid imaging with 123I.
* Thyroxine.
* Amiodarone.
* Iodine-containing contrast media.
* Vitamin preparations.
* Antihistamines.
* Steroids.
* Seafood containing high levels of iodine.
* Iodine-based cough medicine.
* Hair dye.
106
How can drugs used for hyperthyroidism affect the therapeutic effect of radioiodine?
Drugs used for hyperthyroidism (carbimazole and propylthiouracil) interfere with the organification of iodine so would prevent the therapeutic effect of radioiodine.
107
How can interactions between drugs used for hyperthyroidism and radioiodine be prevented?
To prevent this, this treatment should be withdrawn one week before therapy.
108
Drugs used for hypothyroidism (thyroxine and levothyroxine replacement therapy) can interfere with thyroid imaging. How should the drugs be stopped prior to imaging to prevent this?
Thyroxine (T4) has a biological half-life of 7 days and liothyronine (T3) has a biological half-life of 2 days. Therefore, one should stop T4 treatment 28 days before the test. T3 should be used for 14 days then stopped 14 days prior.
109
Which drugs may lead to false negative results with heart investigations with 99mTc Tetrofosmin/Adenosine?
• Beta blockers.
o May blunt the response to exercise-induced stress.
o Should be stopped for 5 half-lives (24-48 hours).
• Calcium channel blockers (e.g. diltiazem and verapamil).
• Dipyridamole.
o Blocks uptake of adenosine.
Patients are also instructed to abstain from caffeine for 12 hours as this can block the adenosine receptor.
110
What are the different monoamine transporters?
* The norepinephrine transporter (NET).
* The dopamine transporter (DAT).
* The serotonin transporter (SERT).
111
Describe mIBG (NET).
mIBG is meta-iodobenzylguanidine and is taken up by the norepinephrine transporter (NET). It is a catecholamine analogue which attaches to receptors in the body. Clinically, it is used to identify the location of tumours such as pheochromocytomas and neuroblastomas.
With I-131 it can be used to eradicate tumour cells that take up and metabolise norepinephrine.
112
What mechanisms of interaction are there which may impact the action of mIBG (NET)?
1. Inhibition of sodium-dependent uptake system – the NET transporter (e.g. TCAs, cocaine, labetolol).
2. Inhibition of uptake by active transport into vesicles – i.e. inhibition of granular uptake within the terminal (e.g. reserpine).
3. Competition for transport into vesicles (e.g. serotonin).
4. Depletion of content from storage vesicles (e.g. labetolol, reserpine).
5. Calcium channel-mediated inhibition (e.g. calcium channel blockers).
113
Which drugs may interact with the noradrenaline transporter hence impacting the activity of mIBG (NET)?
* Reserpine (no longer used in the UK).
* Tricyclic antidepressants.
* Sympathomimetics.
* Neuroleptics.
* Labetolol.
* IV phenoxybenzamine.
* Calcium channel blockers.
* Amiodarone (difficulty of long half-life).
114
WHich drugs should be stopped prior to DaTSCAN?
```
• CNS stimulants:
o Dexamfetamine.
o Methylphenidate.
o Modafinil.
• Antidepressants (Amoxipine).
• Anxiolytics (Buspirone).
• Sibutramine.
• Pimozide.
• Benzatropine.
• Possibly SSRI (sertraline – very weak DAT inhibitors).
• Cocaine.
```
115
What key steps should be followed when stopping medication prior to mIBG or DaTSCAN?
* Medication history taken when arranging mIBG or DaTSCAN.
* Stop interacting drugs for 5 biological half-lives.
* Clinicians must be consulted – particularly important for antihypertensives and neuroleptics.
116
Explain In-Vivo Physiochemical Interactions Between Radiopharmaceutical and Patients Medication.
These are a result of a genuine reaction between a drug and radiopharmaceutical. Little is known about the mechanism of action of these interactions at the molecular level. It is possibly down to the formation of local complexes which alters biodistribution.
117
Explain the interaction between IM iron dextran and MDP.
The MDP is chelated, producing an insoluble complex. Instead of localising throughput the skeleton, activity is observed in the gluteal region at the site of iron injection.
Through that, a local complexation reaction between reduced Tc and ferric hydroxide occurs.
118
Explain the interaction between bisphosphonates and MDP.
Bisphosphonates used for Paget’s cause reduced skeletal uptake of Tc diphosphonates.
Tc can form preferential complexes with circulating bisphosphonates, and so the amount taken up into the skeleton is reduced.
119
Explain the interaction between aluminium and colloids.
Aluminium-containing drugs (e.g. antacids) can interact with colloidal radiopharmaceutical preparations. Aluminium causes colloid particles to flocculate together.
120
Explain Drug-Induced Disease Affecting the Transport of Radiopharmaceuticals.
This occurs when an extension of the expected pharmacological effect or an adverse reaction to a drug alters the biodistribution of the radiopharmaceutical. Many drugs can cause or aggravate the disease, this is known as iatrogenic disease.
121
Drug-induced liver damage could cause altered liver uptake of radiopharmaceuticals. Give some drugs which may cause liver disease.
* Paracetamol, aspirin, tetracycline – reduce liver uptake.
* TPN therapy – cause fatty liver disease.
* Erythromycin – false positive scan with T-BIDA.
* Methotrexate – diffuse accumulation of MDP in the liver.
122
Drug-induced renal toxicity will affect the behaviour of renal imaging agents, or of agents which are renally excreted. Give some drugs which may lead to renal toxicity.
* Aminoglycosides.
* Penicillins.
* Cytotoxics.
* Amphotericin.
* Cyclosporin.
123
The most common drug to cause pulmonary toxicity is bleomycin, which can cause pulmonary interstitial fibrosis, this can cause high lung uptake of 67Gallium citrate. What other drugs may cause abnormal lung uptake?
* Amioderone.
* Busulphan.
* Nitrofurantoin.
124
What other factors may cause unusual handling of radiopharmaceuticals?
* Radiation therapy.
* Diet.
* Degree of hydration – renal studies.
* Caffeine intake.
* Fasting status – affect absorption and motility of the gut.
* Alcohol.
125
What factors may interfere with the radiolabeling of white blood cells?
* White cell count.
* Volume.
* Temperature.
126
What drugs may affect the chemotaxis of leucocytes, leading to incorrect imaging studies?
* Antibiotics.
| * Corticosteroids.
127
Give some examples of rugs which may interfere with leucocyte labelling.
* Calcium channel blockers.
* Captopril.
* Sodium valproate.
* Metronidazole.
* Allopurinol.
* Prednisolone.
* Antibiotics.
* Aspirin.
* Ibuprofen.
* Azathioprine.
* Cyclosporin.
* Cyclophosphamide.
* Doxorubicin.
128
A specific drug may be administered before, during, or after administration of the radiopharmaceutical. For what reasons may this be done?
* Alter organ function.
| * Give diagnostic information as a result of changes in biodistribution, uptake, or excretion.
129
What are the two main categories of nuclear medicine cardiac study?
* Myocardial imaging to assess regional coronary blood flow and give evidence of stenosed (abnormal narrowing) blood vessels.
* Blood pool imaging to determine ventricular function.
130
Which drugs are used to induce cardiac stress for cardiac imaging?
Adenosine, dobutamine, regadenoson (rapiscan).
131
Explain the use of adenosine to cause cardiac stress in cardiac imaging.
Given at a dose of 140mg/Kg/min. The tracer is given after 4 minutes of infusion and adenosine is then continued for 2 minutes more. Adenosine has a half-life of 13 seconds so has to be given continuously.
Unlicensed 100ml minibags are used.
132
Explain the use of dobutamine to cause cardiac stress in cardiac imaging.
Used in asthmatic patients.
133
Explain the use of regadenoson (Rapiscan) to cause cardiac stress in cardiac imaging.
A 400mcg dose is used, with no adjustment made for weight. A 10-second bolus is used, followed by administration of the radiopharmaceutical.
134
Explain the use of furosemide in renal studies.
Prolonged retention of tracer is seen in a dilated, non-obstructed renal system due to ‘reservoir’ effect. Increasing urine flow with a diuretic result in a washout of the activity.
In contrast, an obstructed system will demonstrate progressive accumulation of activity with no response to the diuretic.
Furosemide 40mg IV is given.
135
Explain the use of morphine in hepatobiliary studies.
Morphine is used in the investigation of Sphincter of Oddi dysfunction. Morphine causes constriction of the Sphincter of Oddi.
All prescribed narcotic/opioid analgesics must be withdrawn at least 24 hours before the investigation. A sub-analgesic dose of morphine 2mg IV is used.
136
Which drug is used in infants prior to T-BIDA scan for biliary atresia, to enhance uptake and excretion?
Phenobarbitone.
137
What is used to induce gall bladder contraction and emptying in hepatobiliary studies?
CCK (cholecystokinin) analogue sincalide or a fatty meal is used to induce gall bladder contraction and emptying.
138
When is thyroid blockade necessary in thyroid studies?
Thyroid blockade is necessary if dose to thyroid >50mGy.
139
What is the duration of thyroid blockade needed for different imaging studies?
* 24 hours DaTSCAN.
* 48 hours mIBG.
* 10 days I-131 therapy.
140
What agents can be used as thyroid blocking agents?
* Potassium iodate (85mg x 2 daily) – can induce hyperthyroidism.
* Lugol’s iodine (0.1 – 0.2ml tds) – very unpalatable.
* Potassium iodide – can induce hyperthyroidism.
* Potassium perchlorate (200mg tds) – associated with blood dyscrasias on prolonged use.
141
What are the principles of targeted therapy in radiopharmacy?
The agent must react to the target at an adequate concentration. One should also aim to achieve an adequate target to background radiation ratio, only the tissue targeted should be the one irradiated.
The radiosensitivity of the target organ should also be taken into account; rapidly growing tumours are more sensitive.
142
Why should the appropriate type of radioactive emission, energy and half-life be chosen?
The appropriate type of radioactive emission, energy and half-life should be chosen in an effort to reduce the patient’s exposure to x-rays and gamma photons.
143
What are the advantages of targeted therapy in nuclear medicine?
There can be fewer side effects than external beam radiation. Therefore, targeted therapy reduced this potential for collateral damage. Another main advantage of targeted therapy is that it can target the metastasis as well as the main tumour, should any be thought to exist.
144
What are the disadvantages of targeted therapy in nuclear medicine?
The main disadvantage of targeted therapy is that the patients become a ‘radioactive source’ and there are additional radiation protection requirements.
145
Choice of radionuclide is based upon what characteristics?
The physical half-life of a few days. Simple, cheap production. Energy emission is suitable for the purpose. Type of emission.
146
Why is a simple, cheap production of radionuclides important?
To reduce the chance of radionuclide impurities, increasing the effective concentration. More bang for your buck.
147
What is beneficial about beta minus emitters?
The energy is dissipated within the patient, minimal external radiation hazard.
148
Describe auger electrons.
Therapeutic use limited by difficulties in achieving specific enough targeting.
Short range (<0.5µm) and low energy (few eV to 1 KeV) requires the radionuclide to be internalised into target cells to have an effect.
149
Describe alpha emitters.
Emit high densities of ionisation energy (5-9 MeV) over short path lengths (40-100µm) corresponding to 5-10 cell diameters, resulting in high LET (80-100 keV/µm-1).
Highly toxic to non-target as well as to the target tissue. Can be very effective but needs precise targeting.
Radiation protection and contamination monitoring challenges.
150
What isotopes are commonly used in nuclear medicine?
111In, 90Y, 177Lu, 223Ra.
151
Why is versatile chemistry important when it comes to radionuclides?
Versatile chemistry is required to enable the binding between the ligand and the nuclide. Some radionuclides can be used without any further chemical manipulation (e.g. I-131 sodium iodide, colloidal preparations for intracavity use).
152
To radiolabel amino acids, which form of Iodine is prefered?
Electrophile.
153
What do most radionuclides require for binding to ligands?
A bifunctional chelating agent.
154
Explain the use of Sodium 131Iodide for thyroid disease.
This can be considered a ‘magic bullet’ as it is incorporated into the thyroid metabolic pathway. It is a good, non-invasive alternative to surgery and can also be used to target thyroid cancer metastasis which requires thyroid hormones.
It is used for benign (hyperthyroidism – up to 800MBq) and malignant disease (thyroid carcinoma – several GBq). It emits γ-rays (364 keV) and this causes the patient to become a radioactive source.
155
What is the half-life of sodium 131iodide?
8 days.
156
In what forms can sodium 131iodide come in?
It can come as capsules, oral liquid, or an injection. Lower doses can be given on an outpatient basis whereas higher doses require admission.
157
Explain the dose of sodium 131iodide used for thyroid disease.
The dose given and the effect it has depends on patient factors, it may lead to an underactive thyroid.
158
What patient counselling should be given before sodium 131iodide treatment commences?
Information about the disease and its treatment (all options) should be given to the patient. They should be told how the radioiodine works and should be informed of the need to stop antithyroid medication before treatment as this can block uptake.
The outcomes, including the possibility of the need for repeated doses and the chance of hypothyroidism, should be explained to the patient. This should include side effects/after effects, warn them about the possibility of a thyroid storm.
Finally, one should check for eye disease and smoking status (smoking may exacerbate). Treatment with prednisolone may also be required.
At the end of the consultations, one should ensure that they take any patient questions into account, endeavouring to answer these questions and signpost of this isn’t possible.
159
What radiation protection issues should be taken into account with sodium iodide treatment?
• Excreta are radioactive.
o Urine and to a lesser extent, sweat.
o Good hygiene is important.
o In-patient contamination monitoring is needed.
• Effects on unborn babies.
o Women must not become pregnant for 6 months.
o Men must not father a child for 4 months.
• Breastfeeding must cease permanently.
• Contact with other people must be limited.
o Contact time for adults and children.
o Bad sharing.
o Social contact.
o Travel.
160
Radium-223 is an alpha emitter with the brand name Xofigo. What is it licensed for?
It is licensed for the treatment for metastatic castration-resistant prostate cancer (mCRPC) with symptomatic bone metastasis and no known visceral metastasis. The overall survival of patients when this is given is significantly longer.
161
How is Xofigo supplied?
As a finished product.
162
How is Xofigo (Radium-223) given?
It is given in conjunction with luteinising hormone-releasing hormone (LHRH). The dose given is 55MBq/kg and it is administered by slow IV injections for up to 1 minute. If this is given via a line, one just flushes the line before and after with saline. The dose is given at 4-week intervals for 6 injections.
163
Does Xofigo (Radium-223) require any dose adjustments for renal or hepatic treatment, or for the elderly?
No.
164
When is radium-223 contraindicated? Why?
Radium-223 is contra-indicated in combination with abiraterone acetate or prednisolone. This is because it can increase the risk of fractures and have a trend for increased mortality. These medications should be ceased for 5 days prior to treatment.
