Radioactive Isotopes

Question 1

Ideal characteristics for a treatment source:

Answer 1

● Relatively short half life
● High specific activity (Bq/g)
● Adequate penetration
● Rapid dose falloff

Question 2

Give a list of clinically useful radioactive isotopes:

Answer 2

Caesium-137	
Iridium-125	
Palladium-103
Iodine-125	
Iodine-131	
Phosphorus-32	
Strontium-89	
Strontium-90	
Yttrium-90	
Samarium-153

Question 3

Define

Answer 3

Add something high yield

Question 4

I - 125

Energy spectrum
Energy (Mev)
Half-life
HVL Lead
Specific activity (TBq/g)
Form
Daughter product

Answer 4

I - 125

Pure gamma (i.e electron capture)
Mean 0.025
max 0.036
60 days
HVL 25 um
644 TBq/g
Pellets
Daughter = Tellurium - 125

Question 5

I - 125

Construction
Handling/Pt advice
Clinical Use
Advantage
Disadvantages

Answer 5

Pellets

Handling/Pt advice:
Avoid cremation within 12 months
Wipe test before implant

Use:
Permanent prostate implant

Adv:
Non penetrating energy (pure gamma)

DisAdv:
Relatively long half life
Fragile source

Question 6

I - 131

Energy spectrum
Energy (Mev)
Half-life
HVL Lead
Specific activity (TBq/g)
Form
Daughter product

Answer 6

I -131

90% Beta, 10% gamma
Beta = 0.19Mev, Gamma =0.36Mev
T1/2 = 8 days Teff = 7.3 Days.
HVL = Not relevant.
4600 TBq/g
Form = liquid
Daughter = Xenon 131

Question 7

I - 131

Construction
Handling/Pt advice
Clinical Use
Advantage
Disadvantages

Answer 7

Liquid

Handling/Pt advice:
Lead pot
- Pts require isolation
- Area survey on discharge
- avoid pregnancy within 6 months
- No sex for a month!

Uses:
Radioablation thyroid ca and hyperthyroidism

Advantage - selectively taken up by thyroid (30% by follicular cells)
Disadvantage, liquid can be spilt/regurgitated.

Renal excreted (70% not in thyroid)

Question 8

Samarium - 153

Energy spectrum
Energy (Mev)
Half-life
HVL Lead
Specific activity (TBq/g)
Form
Daughter product

Answer 8

70% Beta, 30% gamma
Beta = 0.23 Mev, Gamma =0.81Mev
T1/2 = 2 days Teff = 2 hrs
HVL = Not relevant.
1602 TBq/g
IV
Daughter?

Question 9

Strontium -90

Energy spectrum
Energy (Mev)
Half-life
HVL Lead
Specific activity (TBq/g)
Form
Daughter product

Answer 9

Pure beta
Beta = 0.54Mev, 
T1/2 = 29 years
HVL = Not relevant.
5.5 TBq/g
Form = Plaque for trigin.
Daughter = Yttrium-90 (last 64hrs)

Question 10

Strontium -89

Energy spectrum
Energy (Mev)
Half-life
HVL Lead
Specific activity (TBq/g)
Form
Daughter product

Answer 10

Beta
0.58Mev
T1/2 = 50.5 days
Specific activity =?
IV

Question 11

Iridium-192

Energy spectrum
Energy (Mev)
Half-life
HVL Lead
Specific activity (TBq/g)
Form
Daughter product

Answer 11

95% Beta

Energy mean 0.38 mean
1.06 max

Half life 74 days

HVL 3mm lead

Specific activity 340 TBq/g

Wires
Barium 137

Question 12

Caesium-137

Energy spectrum
Energy (Mev)
Half-life
HVL Lead
Specific activity (TBq/g)
Form
Daughter product

Answer 12

94% Beta

Half life 30year

HVL 6.5mm lead

3.2 TBq/gram

LDR brachy - rods, poweder, microspheres

Question 13

Palladium-103

Energy spectrum
Energy (Mev)
Half-life
HVL Lead
Specific activity (TBq/g)
Form
Daughter product

Advantage

Answer 13

Pure gamma (electron capture ie p->n, release gamma)

Mean 0.023 (I-131 is 0.024)

Half-life 17days

TBq/g 2775

Pellets/seeds

Same as I-131: non-penetrating energy
Disadvantage - single use, fragile source

Question 14

Phosphous-32

Energy spectrum
Energy (Mev)
Half-life
HVL Lead
Specific activity (TBq/g)
Form
Daughter product

Advantage

Answer 14

Pure beta

1.7 Mev!!!!

14 days

IV

rarely used for bone mets

Question 15

Where does Yettium-90 come from?
Half life?
Uses?

Is an approximate example of what equillibrium:

Answer 15

Strontium 90 (half life 28.8 years)
64 hours
Microspheres
Liver mets…

Secular equilibrium (but not compared to radium 226->radium222)