Linear Accelerator Drift Tube

Positive Ion Cyclotron Operation

CS-15 Positive Ion Cyclotron Washington University School of Medicine

Target

Targets for Cyclotron 1. Metals: 111 Cd(p,n) 111 In( 111 In-DTPA) 201 Hg(d,2n) 201 Tl( 201 Tl-chloride) 68 Zn(p,2n) 67 Ga( 67 Ga-citrate) 2. Gases: 14 N(d,n) 15 O(H 2 15 O, 15 O 2 ) 14 N(p,  ) 11 C( 11 C-acetate, 11 C- palmitate, 11 C- glucose) 3. Liquids: 16 O(p,  ) 13 N( 13 N-ammonia) 18 O(p,n) 18 F( 18 F-FDG)

Simple X-ray Tube

Fast neutrons (E of 1.5 MeV) have a low probability of interaction with other nuclei. They are thermalized or slowed down (0.025 eV) to interact with other nuclei. Moderators (low MW materials like heavy water, beryllium or graphite) are distributed in spaces between fuel rods

University of Missouri Research Reactor (MURR) Columbia, MO

Nuclear Fission 235 U n 236 U Ba Kr n 99 Mo Sn n 236 U unstable - undergoes fission immediately wide range of fission products - usually 1/3 and 2/3 split of the mass number

Fission products useful in nuclear medicine include: 99 Mo, 131 I, 133 Xe, 137 Cs and 90 Sr Mo-99 I-131

Reactor-Produced Radionuclides: Thermal Neutron Reactions (n,  reaction: formed by reactions between targets and thermalized neutrons Y A z + n Y+1 A z +  A=target; A=isotope produced same atomic number, different mass (n,  reaction –not carrier-free, since target and product are same –radioisotopic purity can be high if cross section is sufficiently large (e.g. 176 Lu(n,  ) 177 Lu)

Reactor-Produced Radionuclides: Thermal Neutron Reactions, cont’d (n, p  reaction: formed by reactions between targets and thermalized neutrons Y A z + n Y B z-1 + p A=target; B=isotope produced different atomic number, same mass (n, p  reaction –carrier-free, since target and product are different –example: 64 Zn(n,p) 64 Cu

Fisson/Reactor ProductsCyclotron Products Generally decay by  - emission because of excess neutrons Not many are useful for diagnostic imaging, but several are useful for radiotherapy Generally decay by  + emission or electron capture because of excess protons Many are useful for diagnostic imaging (gamma scintigraphy or positron emission tomography)

Photoelectric Effect: The energy of an incoming gamma ray is completely absorbed by the atom, and the energy absorbed is used to eject an electron from the atom.

Pair Production: The energy of an incoming gamma ray (>1.02 MeV) is completely absorbed by the nucleus, and the energy absorbed is used to eject an electron and a positron from the atom.

Alpen, E.L. (1998) Radiation Biophysics Academic Press, San Diego, p. 87

Alpen, E.L. (1998) Radiation Biophysics Academic Press, San Diego, p. 105

Hall, E.J. (1994) Radiobiology for the Radiologist J.B. Lippincott Company, Philadelphia, p. 154

Latorre Travis, E. (1989) Primer of Medical Radiobiology Year Book Medical Publishers, Inc., Chicago, p. 92

LET RBE Hall, E.J. (1994) Radiobiology for the Radiologist J.B. Lippincott Company, Philadelphia, p. 160

Alpen, E.L. (1998) Radiation Biophysics Academic Press, San Diego, p. 52