Radioactive Isotopes Flashcards
Ideal characteristics for a treatment source:
● Relatively short half life
● High specific activity (Bq/g)
● Adequate penetration
● Rapid dose falloff
Give a list of clinically useful radioactive isotopes:
Caesium-137 Iridium-125 Palladium-103 Iodine-125 Iodine-131 Phosphorus-32 Strontium-89 Strontium-90 Yttrium-90 Samarium-153
Define
Add something high yield
I - 125
Energy spectrum Energy (Mev) Half-life HVL Lead Specific activity (TBq/g) Form Daughter product
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
I - 125
Construction Handling/Pt advice Clinical Use Advantage Disadvantages
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
I - 131
Energy spectrum Energy (Mev) Half-life HVL Lead Specific activity (TBq/g) Form Daughter product
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
I - 131
Construction Handling/Pt advice Clinical Use Advantage Disadvantages
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)
Samarium - 153
Energy spectrum Energy (Mev) Half-life HVL Lead Specific activity (TBq/g) Form Daughter product
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?
Strontium -90
Energy spectrum Energy (Mev) Half-life HVL Lead Specific activity (TBq/g) Form Daughter product
Pure beta Beta = 0.54Mev, 2.27MeV T1/2 = 29 years HVL = Not relevant. 5.5 TBq/g Form = Plaque for trigin. Eye plaque wire (infused on aluminium) Daughter = Yttrium-90 (last 64hrs)
Strontium -89
Energy spectrum Energy (Mev) Half-life HVL Lead Specific activity (TBq/g) Form Daughter product
Beta 0.58Mev T1/2 = 50.5 days Specific activity =? IV
Iridium-192
Energy spectrum Energy (Mev) Half-life HVL Lead Specific activity (TBq/g) Form Daughter product
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
Caesium-137
Energy spectrum Energy (Mev) Half-life HVL Lead Specific activity (TBq/g) Form Daughter product
Gamma
Half life 30year
HVL 6.5mm lead
3.2 TBq/gram
LDR brachy - rods, poweder, microspheres
Palladium-103
Energy spectrum Energy (Mev) Half-life HVL Lead Specific activity (TBq/g) Form Daughter product
Advantage
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
Phosphous-32
Energy spectrum Energy (Mev) Half-life HVL Lead Specific activity (TBq/g) Form Daughter product
Advantage
Pure beta
1.7 Mev!!!!
14 days
IV
rarely used for bone mets
Where does Yettium-90 come from?
Half life?
Uses?
Is an approximate example of what equillibrium:
Strontium 90 (half life 28.8 years)
64 hours
Microspheres
Liver mets…
Secular equilibrium (but not compared to radium 226->radium222)