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aa Radiochemistry > Radioactive substances in medicine 1 > Flashcards

Radioactive substances in medicine 1 Flashcards

1
Q

What are two applications for non-essential (toxic) elements in medicine

A
  1. Therapeutic drugs to treat a disease
  2. Diagnostic imaging agents
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2
Q

What is theranostics

A
  1. Combines treatment with diagnostics
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3
Q

What was discovered from Radon miners

A
  1. Lung cancer risk associated with U mining is result of exposure to Rn gas and Po-218 and Po-210 which are alpha emitters
  2. Alpha emitters interact with superficial tissues of lungs
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4
Q

What are two examples of toxicity of radiometals

A
  1. Plutonium
  2. Polonium-210
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5
Q

Describe how plutonium is an example of the toxicity of radiometals

A
  1. f-block element; Pu(IV) mimics Fe(III) in terms of similar charge/radius ratio, Eo
  2. Often binds more strongly due to high charge (+4)
  3. Fe(III) is a biologically important species which often goes into deeper tissues of biomolecules
  4. Alpha decay of Pu-235 (t1/2 2.86 years) leads to destruction of surrounding tissue
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6
Q

Describe how polonium-210 is an example of the toxicity of radiometals

A
  1. A deadly alpha emitter
  2. Group 16 with S which is in cysteine
  3. Mimics S, Se,Te
  4. Half life 138.4 years
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7
Q

What is way of treating Polonium or plutonium toxicity

A
  1. Chelation therapy
  2. treatment with siderophores, DesFerriOxamine (DFO)
  3. Chelator binds strongly to Fe3+
  4. So also binds to Pu or Po and excretes
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8
Q

What are medical applications of ionising radiation for diagnostics

A
  1. X-rays
  2. Nuclear medicine - SPECT
  3. Positron Emission Tomography - PET
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9
Q

What isotopes are used for SPECT

A
  1. 99mTC - most common
  2. 201TI
  3. 111In
  4. 123I - most common
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10
Q

What isotopes are used for PET

A
  1. 18F - Most common
  2. 68Ga
  3. 89Zr
  4. 64Cu
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11
Q

What are medical applications of ionising radiation for diagnostics

A
  1. X-rays
  2. Radioisotopes
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12
Q

What radioisotopes are used for therapeutics

A
  1. Brachytherapy- 137Cs, 192Ir, 226Ra
  2. Tele-therapy- 60Co
  3. Radiopharmaceuticals- 90Y, 131I, 89Sr, 153Sm, 177Lu, 188Re, 186Re
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13
Q

What is nuclear medicine

A
  1. A field of science that uses the nuclear properties of matter in medical diagnostics and therapy
  2. In diagnosis (radiology), radioactive substances (radiopharmaceuticals) are administered to patients and the radiation emitted is measured (imaged)
  3. Radiation therapy is the medical use of ionising radiation as part of cancer treatment
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14
Q

What kind of scans are there

A
  1. CT- computed tomography- x-ray base; MRI
  2. SPECT- single photon emission computed tomography
  3. PET- positron emission tomography
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15
Q

What is used for MRI as a contrast agent and problem

A
  1. Gd(III) - non radioactive
  2. But partly retained in the brain
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16
Q

What is alternative to Gd(III) for MRI

A
  1. Gamma emitting (99mTc, 111ln)
  2. Or positron emitting (64Cu, 68Ga, 89Zr)
  3. Deemed to be less harmful than Gd
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17
Q

What are examples of radioactive isotopes used for radiotherapy for cancer treatment

A
  1. I
  2. Cu
  3. Re
  4. Y
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18
Q

Contrast resolution for different types of molecular imaging

A
  1. CT/x-ray and US: give good detail about anatomy and physiology of tissue
  2. MRI: Just enough resolution to understand metabolism- how tissue is affected by disease but doesn’t contrast well so better for physiology
  3. PET/NM- good for metabolism and molecular level- good for understanding of onset of disease
  4. Optical- problems as more invasive
  5. Molecular imaging- allows proteins and genome to be seen
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19
Q

Define radioactive decay

A
  1. Unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves
  2. This decay results in an atom of one type called the parent nuclide transforming to an atom of a different type called the daughter nuclide
20
Q

Describe hazard of alpha emission

A
  1. Easily shielded
  2. Considered hazardous if alpha emitting material is ingested or inhaled
  3. Two protons and two neutrons bound together in a particle identical to He nucleus
21
Q

Describe hazard of beta emissions

A
  1. Shielded by thin layers of material
  2. Considered hazardous if ingested or inhaled
  3. High energy, high speed electrons or positrons
22
Q

Describe hazard of gamma emissions

A
  1. Need dense material for shielding
  2. Considered hazardous when external to the body
  3. Form of high energy electromagnetic radiation
23
Q

Which common radioisotopes for imaging and therapy have beta emission

A
  1. C, N, O F, Cu have beta+
  2. Y, Re, I, Cu have beta
24
Q

Which common radioisotopes for imaging and therapy have gamma emission

A
  1. Tc, In, I
25
Q

Which common radioisotopes for imaging and therapy have alpha emission

A
  1. At
26
Q

What is a cyclotron

A
  1. Charged particles are accelerated in an electromagnetic field to high velocities to generate a high energy particle beam
  2. The particle beam can be allowed to hit a target
  3. At sufficiently high energy the collisions lead to nuclear reactions
  4. The atom-by-atom reactions are not suitable for bulk production of new isotopes
  5. Can get medically built ones
27
Q

What is an example of an isotope with a t1/2 compatible with the time needed to achieve optimal tumour-to-background ratios for tracing intact mAbs in living organisms

A
  1. Zr-89
  2. t1/2- 3.3 days
  3. Procedure normally takes a few days
28
Q

What are design requirements for metal-based radiotracers

A
  1. Stable containment of imaging agent
  2. Modulate the lipophilicity- solubilising groups
  3. Use covalent functionalisation - carboxylate units
  4. Biological targeting
  5. Address (targeting): an antibody or related biological molecules incorporating recognition motifs, linked covalently to the main ‘carrier’
29
Q

What are the basic thermodynamic and kinetic properties of metal-chelate complexes

A
  1. High kinetic stability and thermodynamic
  2. koff is most relevant measure for kinetic inertness in vivo - has to stay together in vivo
  3. Ligand metal bond competing with other donors all the time
30
Q

What type of metal complex shows biodistribution at what part of the body

A
  1. Neutral- brain
  2. Cationic- heart
  3. Anionic- kidney
  4. Neutral, lipophilic- liver
  5. Phosphato- bone
31
Q

What is the most common radioisotope used in diagnosis

A
  1. 99mTc
32
Q

What is needed to produce 99mTc

A
  1. 99Mo - Fission radioisotope
  2. Has largest demand out of the fission radioisotopes for medicine
33
Q

Show equation for production of 99mTc

A
  1. 99,42 Mo –> 99m,43Tc + 0,-1e
34
Q

What does SPECT use

A
  1. 99mTc
  2. 123I
  3. 111In
  4. All have half life of a few hours
35
Q

What is SPECT used for

A
  1. Main diagnostic mode
  2. 40% cardiac conditions, 40% oncology
  3. over 100 different imaging procedures
  4. Radiation dose for a 99mTc image is equivalent to an x-ray
36
Q

Describe how SPECT works

A
  1. Diagnosis by imaging (detection of tumours)
  2. Radioisotope accumulates at the site of the disorder and disintegrates emitting a characteristic radiation which is detected
  3. 99m has half life of only 6 hours
  4. The short physical half-life of the isotope and its biological half-life of 1 day - human metabolism, allows for scanning procedures which collect data rapidly but keep total patient exposure low
  5. half-life should match metabolism
37
Q

What is 99mTc used ot image

A
  1. Brain
  2. Skeleton
    3 Kidneys
  3. Thyroid
  4. Heart
38
Q

What are other SPECT relevant isotopes and what are they used to image

A
  1. 201Ti- heart
  2. 123I- thyroid
  3. 67Ga- tumours and abscesses
  4. 52Fe- bone marrow
  5. 133Xe- lungs
39
Q

What is the decay product of Mo-99

A
  1. Tc-99m - a metastable radioisotope of Tc
40
Q

Why is Tc-99m used most frequently for SPECT

A
  1. its 140.5keV gamma-ray emission
  2. its convenient half-life of 6 hours- short physical half-life vs biological half-life of 1 day
  3. Its practical availability to hospitals in the form of Mo-99/Tc-99m generators
41
Q

Describe radiation hazard of production Tc-99m

A
  1. B- electrons emitted are easily shielded for transport to hospitals
  2. 99mTc generators are only minor radiation hazards, mostly due to secondary x-rays produced by the electrons
42
Q

Describe production of Tc-99m

A
  1. 99mTc forms through 99Mo decay and is chemically extracted from the Tc-99m generator
  2. Most generators use column chromatography
  3. Within the generator, Mo-99 is trapped within Al2O3 packed columns in the chemical (radioactive) form 99MoO4 2-
  4. This continually decays to corresponding 99mTcO4 - (pertechnetate ions)
43
Q

How is 99m-Tc separated from 99-Mo in the generator

A
  1. 99mTcO4 - binds less strongly to the alumina columns
  2. Therefore it can be selectively eluted from the columns, by passing standard saline solution
44
Q

How is the purity of Tc-99 checked

A
  1. Using radioHPLC or radioTLC with gamma detectors
45
Q

Once Tc-99m has been eluted from the generator what needs to happen to generate a useful diagnostic tool for SPECT

A
  1. Rapid coordination and stabilisation within a ligand
  2. The entire construct can then accumulate in a particular part of the body of medical interest

aa Radiochemistry (11 decks)

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