Linear Accelerator Drift Tube

Positive Ion Cyclotron Operation

CS-15 Positive Ion CyclotronWashington University School of

Medicine

Target

Targets for Cyclotron

1. Metals:111Cd(p,n)111In (111In-DTPA)201Hg(d,2n)201Tl (201Tl-chloride)

68Zn(p,2n)67Ga (67Ga-citrate)

2. Gases:14N(d,n)15O (H2

15O, 15O2)14N(p,)11C (11C-acetate, 11C-

palmitate, 11C- glucose)

3. Liquids:16O(p,)13N (13N-ammonia)18O(p,n)18F (18F-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 distributedin spaces between fuel rods

University of Missouri Research Reactor (MURR)Columbia, MO

Nuclear Fission

235U144 + n 236U144

236U144144Ba88 + 89Kr53 + 3n

99Mo42 + 135Sn50+ 2n

• 236U 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:99Mo, 131I, 133Xe, 137Cs and 90Sr

Mo-99 I-131

Reactor-Produced Radionuclides:Thermal Neutron Reactions

• (n, reaction: formed by reactions between targets and thermalized neutrons

YAz + n Y+1Az +

A=target; A=isotope producedsame 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. 176Lu(n,)177Lu)

Reactor-Produced Radionuclides:Thermal Neutron Reactions, cont’d

• (n, p reaction: formed by reactions between targets and thermalized neutrons

YAz + n YBz-1 + p

A=target; B=isotope produceddifferent atomic number, same mass

• (n, p reaction– carrier-free, since target and product are different– example: 64Zn(n,p)64Cu

Fisson/Reactor Products Cyclotron 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

RB

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

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

Alp

en, E

.L. (

1998

) R

adia

tion

Bio

phys

ics

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, San

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