Auger emitters

1
Auger emitters

• Decay by electron capture, internal conversion,
  isomeric transition
• ? vacancy in inner electron shell
• ? filled from outer shells
• ? energy loss through electron emission
• Includes Auger, Coster-Kronig, super CK

2
Auger emitters

• Low energy electrons 10 eV - 10 keV
• Short range 1 nm - 1 ?m
• Large numbers 4 - 30
• eg. 55Fe ? 5
• 125I ? 25
• Variable proportion of
• total energy of emissions 55Fe 72
• 125I 12
• 99mTc lt 1

3
Ratio of estimated dose to nucleus assuming
concentration in specified region compared with
uniform distribution
Faraggi et al. 1998
4
RBE of Auger emitters

• Extensive studies of biological effects
• ? in vivo rodent spermatogenesis
• ? in vitro human and rodent cell lines
• Iodine-125 most extensively studied
• RBE cf. 250 kVp x rays
• 7 - 9 when covalently bound to DNA
• 4 - 5 in nucleus
• ? 1 in cytoplasm

5
Radiation protection and Auger emitters

• Radionuclide specific
• Extremely low environmental levels
• Potential importance in nuclear medicine
• ? cellular/sub-cellular distribution of new
  radiopharmaceuticals
• Review Bingham et al. The problem of Auger
  emitters for radiological protection. Rad.
  Prot. Dosim. 92, 219-228 (2000)

6
Zinc-65 and prostate cancer

• Rooney et al (1993)
• Case - control study of UKAEA workers
• ? prostate cancer increase
• ? exposures to 3H, 51Cr, 59Fe, 60Co, 65Zn
• Bingham et al (1997) Zn biokinetics/ doses
• ? uptake by prostate 0.5
• ? concentration in 1/10th of prostate
• ? uptake of 20 in prostate cell nuclei
• ? RBE of 20 for Auger emissions
• 65Zn dose 27 x ICRP

7
Zinc-65 and prostate cancer

• Bingham et al (1997)
• For inhalation of 3H, 51Cr, 59Fe, 60Co, 65Zn at
  1 ALI over 10 years -
• prostate dose ? 100 mSv (80 mSv from 65Zn)
• ? 100 times too low to account for prostate
  cancer excess

8
RBE for Zinc-65

• Bingham et al (2000)
• Chromosome aberrations in rat prostate cells in
  vitro
• 1 - 5 for 65Zn cf gamma rays
• Kreihuber and Simko (2000)
• Apoptosis / micronuclei in human carcinoma cell
  line (SCL-II)
• 1 - 3 for 65Zn cf x rays