Radiopharmaceuticals and Radioactive Decay

alpha decay

helium nucleus

ex) 263Sg —> 259Rf + 4He

alpha decay hazard

via ingestion or inhalation of alpha emitter

alpha decay blocked by

paper and dead layer of skin

beta decay 

energetic electron singly ionized 

ex) 14C —> 14N + e- + ve

beta decay hazard

external hazard to skin and eyes 

internal hazard via ingestion or inhalation of beta emitter 

beta decay blocked by

plastic

gamma decay 

x rays and gamma rays are photons (no charge) 

ex) 152Dy —> 152Gy + gamma 

gamma decay hazard

external hazard to deep organs and tissues

internal hazard via ingestion or inhalation of gamma emitter

gamma decay blocked by 

lead

where do we get majority of our background radiation from?

radon

what is a radioisotope

same number of protons, different number of electrons

same atomic number but different mass

unstable and undergo radioactive transformations

half life equation

t 1/2 = 0.693/λ

sodium iodide-123

diagnose thyroid function

emits gamma rays

iodine-131

diagnostic procedures involving thyroid

treatment of thyroid disorders

technetium-99m

gamma photons for imaging without the hazard of beta particles 

binding agent, kits available to prep compounds 

assist in hepatobiliary imaging and ischemic heart disease 

strontium-89 chloride 

decays by beta emission 

used for bone scans 

acts like calcium analogues (clears rapidly from bloodstream and localizes in bone mineral) 

toxic —> cant give to patients with platelets < 60,000 or WBC <2400

yttruim-90

beta emitting

used in radioimmunotherapy of solid large tumors and lymphomas

uses therasphere - insoluble glass microspheres that are used for hepatocellular carcinoma (bind yttruin-90) and stay localized in the liver minimizing side effects

thallous-201 chloride

used for visualization of myocardial infarction or ischemic heart disease

gallium-67 citrate 

localized in viable primary and metastatic tumors and in focal sites of infection 

used in Hodgkin’s disease, lymphomas, and bronchogenic carcinoma 

used for diagnosing and monitoring of fever of undetermined origin and for pneumocystis cavinii pneumonia of AIDS

disadvantage = considerable biological variation 

imaging

following administration of a radiopharmaceutical to the patients a gamma camera is used to image the area of interest

gamma camera

used to know how the radiopharmaceutical distributes itself throughout the body or is taken up by specifically targeted organs

can be still and dynamic images

SPECT imaging 

single photon emission computed tomography 

look at patient from many different angles presented as a series of planes 

can demonstrate precise detail within the patient

PET imaging 

positron emission tomography 

used to study physiologic and biochemical processes within the body 

used for mapping regional blood flow and volume, oxygen metabolism, bone remodeling, tumor receptor density, reporter gene expression, etc. 

chemical changes often occur prior to anatomical changes in body and these can be detected by PET

can be used in pharmacokinetic distribution evaluations and to see if a drug reaches a specific receptor site