1 Common Lab Sources

2 Radioactive Sources

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

4 Radionuclides in Medicine  Nuclear medicine Diagnostic  Permits functional imaging (biochemistry and metabolism versus anatomical structure)  >80% of all procedures use 99m Tc  Radiotherapy Therapeutic  Primarily for cancer treatment  External beam – teletherapy using 60 Co 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/  eff = 1/  radioactivity + 1/  biological 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  99m Tc is used in ~ 80% of diagnostic procedures 99m Tc pertechnetate (TcO 4 - ) 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 t 1/2 =6.02 hrs  Decay scheme Which is (are) the medically useful gamma(s)?

10 Technetium – 99m  A closer look There is no  1 emission, it IC’s IC competes with  2 IC competes with  3 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  90 Sr/ 90 Y for eye lesions  90 Sr/ 90 Y, 90 Y, 32 P 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 226 Ra -> 222 Rn +  -> … -> 206 Pb  Although rarely used now, it’s a good reaction to know given its historical significance

17 Brachytherapy  Sources 226 Ra -> 222 Rn +  -> … -> 206 Pb  Which equilibrium is achieved (t 1/2 ( 226 Ra) = 1600 years)?  222 Rn is a radioactive gas  About 50 gamma energies are possible ranging from 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  = 8.25 R-cm 2 /hr-mCi

18 Brachytherapy  Sources More modern replacements for 226 Ra are 137 Cs  Familiar gamma ray spectrum with E=0.662 MeV  t 1/2 =30 yrs and  =3.26 R-cm 2 /hr-mCi and 192 Ir  More complicated gamma ray spectrum with = 0.38 MeV  t 1/2 =73.8 days and  =4.69 R-cm 2 /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 235 U fission produced Neutron activated Both produce neutron rich radionuclides  Cyclotrons Uses charged particle beams (p, d, t,  ) Produces proton rich radionuclides Secondary source  Radionuclide generators

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

23 Nuclear Reactors  Nuclear reactor schematic

24 Fission Production  Nuclei such as 99 Mo, 131 I, and 133 Xe are produced in the fission products using an enriched 235 U target (HEU – 90%)  Complex chemical processing (digestion or dissolution) and purification separates the 99 Mo 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 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  18 F is the most common radionuclide in PET oncology Are important elements of all biological processes hence make excellent tracers  18 F is used to label FDG ( 18 F-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 t 1/2 for 18 F = 110 minutes

29 Cyclotron Production  18 F 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  99 Mo (67 hours) decaying to 99m Tc (6 hours) Sodium pertechnetate (NaTcO 4 ) results which can then be combined with an appropriate pharmaceutical Developed at BNL, a particle and nuclear physics lab Other generators also exist ( 69 Ge to 68 Ga, 82 Sr to 82 Rb, …)

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 TcO 4 - but not the MoO 4 - The elute is thus Na + TcO 4 - (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