Lesson 16

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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