4. Isotopes and their applications in medical practice.

Stable application of isotopes

Meselson-Stahl experiment (Proof of N-inclusion)

Urea exhalation test (identification of Helicobacter pylori

Radioactive/Unstable applications of isotopes

Sensitive concentration determination

Trace methods

2D and 3D imaging (camera, SPECT, PET)

Therapy

Most commonly used isotopes

2H, 13C, 15N, 18O

Radiation inside the body: a and b radiation

limited penetration depth (a-particles: typically 10-100 microm in tissues; b(-)-particles: a couple of millimeters)

only topical application

Radiation outside the body: electron radiation

electron radiation is generated in accelerators

adjustable energy (discrete spectrum)

adjustable penetration depth • damage is continuous from the skin to the tumor

Radiation outside the body: proton radiation

• proton radiation is generated in accelerators, adjustable energy (discrete spectrum)  adjustable penetration depth

due to the presence of the Bragg peak the dose is delivered primarily to the tumor • very expensive since protons have to be accelerated to a large energy

Radiation outside the body: gamma radiation and x ray

Cobalt therapy • quantized gamma energies • absorption and depth-dose decay approximately exponentially with penetration depth