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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