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PHAR 262 > Iodine Labelling Radiopharm > Flashcards

Iodine Labelling Radiopharm Flashcards

1
Q

which iodine isotope was commonly used for in vitro procedures?

A

I-125

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2
Q

NaI (sodium iodide) is (un/labelled).

A

unlabelled

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3
Q

half life for I-123

A

13.2 hrs

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4
Q

half life for I-131

A

8.05 days

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5
Q

decay method/product of I-123

A

electron capture
123Te

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6
Q

decay method/product of I-131

A

negatron decay (B- emission)
131-Xe

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7
Q

photon energy for I-123

A

159 keV (83%), 27 keV x-rays (71%)

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8
Q

photon energy for I-131

A

364 keV (82%), 637 keV (7%)

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9
Q

between I-131 and I-123, what can be used for imaging? for therapy?

A

imaging - I-123 (I-131 can also but not ideal)

therapy - I-131

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10
Q

mode of production for I-123

A

cyclotron

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11
Q

mode of production for I-131

A

fission (or neutron activation)

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12
Q

what is I-123 used for?

A
  • thyroid uptake and scan
  • WB scan for thyroid mets
  • labelled to MIBG for adrenal medulla imaging
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13
Q

what is I-131 used for?

A
  • therapy for thyroid ca and hyperthyroidism
  • labelled to MIBG for imaging or to treat specific malignancies
  • thyroid uptake and scan
  • WB scans
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14
Q

what are the three oxidation states iodine can exist in?

A

1-, 0, 1+

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15
Q

what causes oxidation of iodine?

A

acidity, free radicals and free radical byproducts
heat and light accelerates oxidation runs
high conc of radioactivity
Cl- ions

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16
Q

oxidation is more of an issue with ___. why?

A

I-131
beta emission causes more radiolysis and more free radicals
has longer half-life and higher energy

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17
Q

what is done to limit oxidation?

A
  • using buffer to keep pH 7-8.5
  • addition of reducing agents and antioxidants
  • low amts of activity
  • diluting with dH2O to limit presence of Cl-
  • adding EDTA (chelating agents)
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18
Q

what does EDTA do?

A

binds with extraneous metals to prevent them from causing oxidation

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19
Q

radioiodination

A

labelling with radioiodine

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20
Q

two methods for radioiodination

A
  1. isotope exchange
  2. introduction of foreign label
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21
Q

isotope exchange

A

swapping stable nuclide
(I-127 exchanged for radio iodine)

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22
Q

which radioiodination method requires iodide to be oxidized first?

A

intro to a foreign label

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23
Q

iodine is most commonly labelled to ___.

A

proteins
ring structures in amino acids or other organic molecules

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24
Q

3 forms of I-131

A

solution, capsule, fillable capsule

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25
Q

what form is dose activity adjusted?

A

solution and fillable capsule

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26
Q

what form is dose activity not able to be adjusted?

A

capsule

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27
Q

what do I-131 capsules contain?

A
  • dibasic sodium phosphate (absorbing buffer)
  • sucrose filler
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28
Q

when I-131 is administered orally, it clears the gastrointestinal tract by __ hrs and goes where?

A

1-2 hrs, and gets reabsorbed into the bloodstream

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29
Q

faster reabsorption into bloodstream in (hypo/hyper)thyroidism pts

A

hyper

30
Q

I-131 is used by the body to produce which hormones?

A

T3 and T4

31
Q

organification

A

use of I-131 by the thyroid to produce thyroid hormones
“body using it for its natural purpose”

32
Q

where does I-131 localize?

A

stomach

33
Q

how is I-131 secreted?

A

by the gastric mucosa

34
Q

when do we typically see liver uptake in thyroid scans? why?

A

we usually see liver uptake in post-therapy images
this is because we will be using higher doses. the body (thyroid) will use the radioiodine to produce T4, which localizes in the liver.

35
Q

where are additional uptake of I-131?

A

salivary glands, breast milk and crosses placental barrier

36
Q

what is method of excretion for I-131?

A

kidneys/bladder

37
Q

uses for I-131?

A
  • thyroid uptake procedures
  • WB imaging for thyroid Ca
  • ablation of thyroid Ca
  • hyperthyroidism
  • thyroid gland scanning
38
Q

dose of I-131 for thyroid uptake?

A

0.15-0.37 MBq

39
Q

dose of I-131 for WB imaging?

A

37 - 185 MBq

40
Q

dose of I-131 for thyroid imaging?

A

3.7 MBq
*low dose so image quality will be poor therefore, Tc-99m preferred for thyroid imaging

41
Q

what is the range of I-131 used for thyroid ca therapy?

A

1110-7400 MBq

42
Q

what range of I-131 is used for remaining thyroid tissue?

A

30-100 mCi

43
Q

what is the difference between regional mets vs. distant mets?

A

regional mets = mets in chest area (not far from region of origin)

distant mets = met is elsewhere in the body

44
Q

what is the range of I-131 used for regional mets?

A

150 mCi

45
Q

what is the range of I-131 used for distant mets?

A

200 mCi

46
Q

thyroid ca therapy is patient dependent, what’s used to determine the appropriate dose?

A

specific absorbed dose to residual tissue and where the mets is seen

47
Q

hyperthyroidism therapy is patient dependent, what’s used to determine the appropriate dose?

A

pt’s thyroid uptake, U/S results and type of pathology

48
Q

what is the dose used for hyperthyroidism therapy?

A

370-1110 MBq

49
Q

what are the three methods to determine the dose used for hyperthyroidism?

A
  1. fixed dose
  2. dose per mass
  3. radiation absorbed mass*
    *most patient specific
50
Q

fixed dose

A

patients with similar pathology get the same dose

51
Q

dose per mass

A

biological uptake and gland weight are considered
2-7 MBq/g

52
Q

radiation absorbed dose

A

biological uptake, gland weight and effective half-life are considered

53
Q

QC for I-131

A
  • visual check
  • expiry check (14 days to 5 weeks)
  • proper storage
  • pH 7.5-9.0
54
Q

dose of I-123 for thyroid uptake

A

1.85 - 3.7 MBq

55
Q

dose of I-123 for WB imaging

A

up to 37-74 MBq

56
Q

Dose of I-123 for thyroid imaging

A

7.4-22.2 MBq

57
Q

what is the shelf-life for I-123?

A

30 hrs

58
Q

Azedra

A

I-131 MIBG

59
Q

AndreView

A

I-123 MIBG

60
Q

I-123 MIBG vials contains

A

370 MBq of activity

61
Q

I-131 MIBG diagnostic vials contain

A

1110 MBq

62
Q

I-131 MIBG therapeutic vials contain

A

12,500 MBq

63
Q

which vial is frozen?

A

I-131 MIBG

64
Q

how does labelling radioiodine and MIBG occur?

A

isotope exchange
(radioiodine replaces stable iodine)

65
Q

MIBG is an analogue of ____.

A

norepinephrine

66
Q

localization of MIBG

A

adrenal medulla

67
Q

what is the main use of MIBG?

A

localization of neuroendocrine tumours

68
Q

where do you see uptake of MIBG?

A
  • tissues with extensive sympathetic innervation (salivary glands, nasopharynx, heart)
  • liver/spleen
  • adrenal medullas
69
Q

MIBG route of excretion

A

kidneys/bladder

70
Q

critical organ for MIBG

A

I-123: bladder wall, liver
I-131: salivary glands

PHAR 262 (12 decks)

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