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Common Lab Sources

Common Lab Sources. Radioactive Sources. Radionuclides in the AZ Particle Lab. Gamma 60 Co @ 1uC 241 Am, 133 Ba, 137 Cs, 60 Co, 88 Y, 22 Na, 64 Mg, 203 Hg, 57 Co @ 10 uC X-ray 55 Fe 5.90 keV (24.4%) and 6.49 keV (2.86%) Beta 90 Sr/ 90 Y @ 50 mCi, 5 mCi, 2mCi, 0.5mCi Alpha

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Common Lab Sources

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  1. Common Lab Sources

  2. Radioactive Sources

  3. Radionuclides in the AZ Particle Lab • Gamma • 60Co @ 1uC • 241Am, 133Ba, 137Cs, 60Co, 88Y, 22Na, 64Mg, 203Hg, 57Co @ 10 uC • X-ray • 55Fe • 5.90 keV (24.4%) and 6.49 keV (2.86%) • Beta • 90Sr/90Y @ 50 mCi, 5 mCi, 2mCi, 0.5mCi • Alpha • 241Am @ 5 mCi

  4. Radionuclides in Medicine • Nuclear medicine • Diagnostic • Permits functional imaging (biochemistry and metabolism versus anatomical structure) • >80% of all procedures use 99mTc • Radiotherapy • Therapeutic • Primarily for cancer treatment • External beam – teletherapy using 60Co units • Internal – brachytherapy using small, encapsulated sources • Notes • 90% of all radionuclide use in medicine is diagnostic • Use of term “radioisotope” is common • Will there be a shortage of radionuclides in the future?

  5. Radionuclides in Medicine • George de Hevesy • Nobel in 1943 for use of isotopes as tracers for chemical processes • A failed experiment to separate Radium-D (210-lead) from lead (206-lead) • The landlady’s leftovers

  6. Radionuclides for Diagnosis • What are the characteristics of an ideal radionuclide for diagnosis? • Half-life? • Effective half-life 1/teff = 1/tradioactivity + 1/tbiological • Type and energy of radiation? • Production and expense? • Purity? • Target area to non-target ratio?

  7. Radionuclides for Diagnosis • The ideal gamma energy (for gamma camera use) is between 100 and 250 keV

  8. Nuclear Medicine • 99mTc is used in ~ 80% of diagnostic procedures • 99mTc pertechnetate (TcO4-) is mixed with an appropriate pharmaceutical (biological construct) for use for • Cardiac imaging and function • Skeletal and bone marrow imaging • Pulmonary perfusion • Liver and spleen function • Cerebral perfusion • Mammography • Venous thrombosis • Tumor location

  9. Technetium – 99m • Half-life t1/2=6.02 hrs • Decay scheme • Which is (are) the medically useful gamma(s)?

  10. Technetium – 99m • A closer look • There is no g1 emission, it IC’s • IC competes with g2 • IC competes with g3 • X-ray and Auger electron emission can also occur

  11. Radionuclides for Therapy • Brachytherapy • Brachys = short • Brachytherapy uses encapsulated radioactive sources to deliver a high dose to tissues near the source • Provides localized delivery of dose • But the tumor must be well localized and small • Proposed by Pierre Curie and, independently, Alexander Graham Bell shortly after the discovery of radioactivity • Inverse square law determines most of the dosimetric effect

  12. Brachytherapy • Used to treat a variety of cancers • Prostate • Gynecological • Eye • Skin • Only ~10% of radiotherapy patients are treated via brachytherapy

  13. Brachytherapy • Sources • Most of the sources used emit gammas • Lower gamma energies are preferred for radioprotection

  14. Brachytherapy • Sources • But a few emit betas • 90Sr/90Y for eye lesions • 90Sr/90Y, 90Y, 32P for preventing restenosis after angioplasty • In general, alphas and betas are absorbed by encapsulation to avoid tissue necrosis around the source

  15. Nanotargeted Radionuclides • Use monoclonal antibodies to carry a radionuclide payload

  16. Brachytherapy • Sources • 226Ra -> 222Rn + a -> … -> 206Pb • Although rarely used now, it’s a good reaction to know given its historical significance

  17. Brachytherapy • Sources • 226Ra -> 222Rn + a -> … -> 206Pb • Which equilibrium is achieved (t1/2(226Ra) = 1600 years)? • 222Rn is a radioactive gas • About 50 gamma energies are possible ranging from 0.184 to 2.45 MeV, though on average there are 2.2 gammas emitted for each decay • The average energy (filtered by 0.5 mm of Pt) is 0.83 MeV • The exposure rate constant (assuming 0.5 mm of Pt) is G = 8.25 R-cm2/hr-mCi

  18. Brachytherapy • Sources • More modern replacements for 226Ra are 137Cs • Familiar gamma ray spectrum with E=0.662 MeV • t1/2=30 yrs and G=3.26 R-cm2/hr-mCi • and 192Ir • More complicated gamma ray spectrum with <E> = 0.38 MeV • t1/2=73.8 days and G=4.69 R-cm2/hr-mCi

  19. Brachytherapy • Methods of delivery • LDR (0.4-2 Gy/hr) versus HDR (> 12 Gy/hr) • Temporary versus permanent • Intracavity versus interstitial • Also surface, intraluminal, intravascular, intraoperative • Seeds, needles, tubes, pellets, wire

  20. Brachytherapy

  21. Radionuclide Production • How are radionuclides made? • Primary sources • Nuclear reactors • 235U fission produced • Neutron activated • Both produce neutron rich radionuclides • Cyclotrons • Uses charged particle beams (p, d, t, a) • Produces proton rich radionuclides • Secondary source • Radionuclide generators

  22. Nuclear Fission • Fission of 236U* yields two fission nuclei plus several fast neutrons

  23. Nuclear Reactors • Nuclear reactor schematic

  24. Fission Production • Nuclei such as 99Mo, 131I, and 133 Xe are produced in the fission products using an enriched 235U target (HEU – 90%) • Complex chemical processing (digestion or dissolution) and purification separates the 99Mo from chemically similar elements and radiocontaminents • The result is a high specific activity (Bq/kg), carrier free nuclide • This means there is no stable isotope of the element of interest • Some negatives are the potential proliferation of HEU targets and radioactive waste

  25. Neutron Activation • An alternative use of reactors is to produce radionuclides via neutron activation • Two drawbacks of this method are • Small activation fraction • Chemically similar carrier that cannot be separated

  26. Cyclotrons • We will cover accelerator physics later in the course

  27. Cyclotron Production • Cyclotron energies can be a few MeV to a few GeV • Laboratory/university or hospital based • Beam currents of 40-60 uA • Produces Ci-level radioisotopes Siemens Eclipse

  28. Cyclotron Production • The reactions shown on the previous page • Are proton rich -> decay by e+ emission or EC • 18F is the most common radionuclide in PET oncology • Are important elements of all biological processes hence make excellent tracers • 18F is used to label FDG (18F-fluorodeoxyglucose) • Useful because malignant tumors show a high uptake of FDG because of their high glucose consumption compared with normal cells • Have short lifetimes (O(minutes)) • Except t1/2 for 18F = 110 minutes

  29. Cyclotron Production • 18F in PET/CT

  30. Cyclotron Production • Alzheimer’s diagnosis

  31. Radionuclide Generators • Generates a radionuclide by exploiting transient equilibrium • Most important application are moly generators • 99Mo (67 hours) decaying to 99mTc (6 hours) • Sodium pertechnetate (NaTcO4) results which can then be combined with an appropriate pharmaceutical • Developed at BNL, a particle and nuclear physics lab • Other generators also exist (69Ge to 68Ga, 82Sr to 82Rb, …)

  32. Radionuclide Generators • Procedure • A glass column is filled with aluminum oxide that serves as an adsorbent • Ammonia molybdenate attaches to the surface of the resin • A sterile saline (the eluant) solution is drawn through the column • The chloride ions exchange with the TcO4- but not the MoO4- • The elute is thus Na+TcO4- (sodium pertechnetate)

  33. Radionuclide Generators • Technetium cow

  34. Radionuclide Generators • Generator schematic

  35. Radionuclide Generators • Generally shipped weekly and milked daily

  36. Gamma Camera • These images are made using gamma cameras • We will cover the details of these (and similar detectors) in upcoming lectures

  37. Gamma Camera • A schematic of a standard gamma camera

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