Lesson 16

Nuclear Medicine

What is Nuclear Medicine? •  Diagnosis and Treatment of Disease using

small amounts of radio-nuclides (radiopharmaceuticals)

•  In diagnosis (imaging) emitted radiation is detected by special detectors (cameras) from injected radio-nuclides to give real time 3 D images of the body.

•  In treatment, radio-nuclides are injected into the body, concentrated in the organ of choice and damage the tissue.

Importance of Nuclear Medicine to students

•  Combines nuclear and radiochemistry, pharmacy, medicine, and radiation biology.

•  Nuclear medicine is a major employer of today’s nuclear and radiochemists, with an ever increasing demand for trained people.

•  Six figure starting salaries

Special properties of 99Tcm

•  142.7 keV gamma ray just perfect for imaging

•  6 hour t1/2 minimizes radiation dose yet is tractable for hospital procedures

•  10 million procedures per year in the US

The 99Mo-> 99Tc decay is an example of transient equilibrium

Milking

Production of 99Mo

Details and Problems

•  Currently AECL/MDS Nordion supply 40% of the world’s demand for 99Mo/99Tc.

•  Chemistry is performed on the irradiated targets by AECL resulting in a 99Mo soln.

•  The soln is shipped to MDS Nordion where it is loaded on the column and distributed.

•  The US demand requires about 34,000-46,000 Ci are produced per week.

What is the Crisis? •  These old reactors are nearing the end of

their lifetime and their operation is not reliable.

•  Recently the Canadian and Dutch reactors underwent prolonged shutdowns

•  US use of 99Mo was curtailed and rationed. •  President Obama gave orders to Steven

Chu (Sec. of Energy) to “solve the problem.”

Special Problems for the US •  We have no domestic supply of 99Mo. US

production was stopped in 1989. (It was claimed that non-US suppliers were subsidized and we could not compete.)

•  High cost production facilities, risk of reactor operations, low market price

•  The best techniques involve the use of HEU (19.7 % 235U) which poses a national security problem.

•  The waste from the production is significant.

Positron Emission Tomography (PET)

•  PET imaging provides quantitative information about biochemical and physiological processes, in vivo

•  A tracer containing a positron emitter is injected, it decays emitting positrons and one detects the two 0.511 MeV photons resulting from the annihilation of the positron-electron interaction.

Special things you can do with PET

•  Real time imaging of brain functions. Effect of drugs, Alzheimer’s disease, psychiatry.

•  90% of use in oncology •  Pharmacology

Therapy •  Oldest aspect of nuclear medicine •  Idea is to use radiation to kill unhealthy cells •  Problem is to do this without killing all the

healthy cells. •  A problem is that cancer cells are less

oxygenated than normal cells and are more radiation resistant.

•  One trick is physical location, ie, fix the radionuclide in a cancer cell so that the decay will preferentially damage the cancer cell.

Tricks •  BNCT (Boron neutron cancer therapy) •  Attach boron compounds to tumor

locations. •  Boron has a very high thermal neutron

capture cross section •  n+10B-> 11B->7Li + 4He

•  Re-oxygenation

Bragg  Curve  Dosimetry  

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