Radiation Toxicity Flashcards
Radiation – definition
Electromagnetic waves or subatomic particles
* Have energy
The Electromagnetic Spectrum
The Electromagnetic Spectrum
- Take-home points:
- The higher energy waves are important
considerations in health (toxicity) - These include:
- UV (A, B, C; in order of increasing energy)
- X-rays
- Gamma rays
Subatomic particles
Alpha Particle Decay (-decay)
- This decay process occurs only for radionuclides with Z > 83 (Z = 83
is bismuth). - The emitted particle is 2 p + 2 n, ejected from the nucleus. This
assembly has a double positive charge and a mass of about 4 AMU. - The -particle has a kinetic energy between about 4 - 8 MeV, and is
monoenergetic for a particular radionuclide decay. - The biological hazard from -particles is due to their high
kinetic energy and double positive charge. - These large particles are not very penetrating and are easily
absorbed by a few centimeters of air or micrometers of water or
tissue.
Lethal poisoning
Ex-spy Alexander Litvinenko was found
with high amounts of 210Po
-Traces found at home, hotel, and sushi bar.
- hours after sushi, he became ill
- seafood is known to contain polonium
210Po – half-life of 138 days.
* 1 mg 210Po ~ 4.5 g of 226Ra (half-life 1600 y) in terms of alpha particles emitted.
Drugs
- XOFIGO®
(radium Ra 223 dichloride). Marketed in
Canada by Bayer - Indication: castration-resistant prostate cancer
- MOA: alpha emitter. Ra mimics Ca, and gets taken up
into bone. - Target: bone metastases
- It’s specificity, elimination and short half-life
minimizes toxicity
Beta Particle Decay (β— decay, negatron)
- This decay mode is characteristic for unstable nuclides with an
excess of neutrons in the nucleus (so called “neutron rich” species). - In the decay process, a neutron spontaneously converts to a proton
and a beta particle. The proton remains in the nucleus while the beta
particle is ejected. - The emitted particle is called a beta particle and has a mass of
0.00055 AMU and a negative charge of 1.6 10-19 coulomb. - This particle is identical to an electron
Positron decay (β+
-decay)
This decay mode is characteristic for unstable radionuclides with an
excess of protons in the nucleus (so called “proton rich” or “neutron
poor” species).
* A proton spontaneously converts to a neutron and a positively
charged beta particle (β
+
-particle). The neutron remains in the
nucleus while the β
+
-particle is ejected.
* The emitted particle is called a positron and has a mass of 0.00055
AMU and a positive charge of 1.6 x 10-19 coulomb. β
+
-Particles are
similar to β
-
-particles in their penetrating ability.
* This particle is similar to a positively-charged electron
Isomeric transition
- Important because it is the primary decay mechanism
of technetium radiopharmaceuticals - A handful of radionuclides have long-lived intermediate states of seconds, minutes or hours.
- The excited state is called metastable and is indicated
by a superscripted ‘m’ . - These metastable states will eventually go to the
ground state with the release of the energy in the form
of a gamma ray. - This decay process is called isomeric transition (IT).
- The metastable species 99mTc is a very important
medical imaging radionuclide which decays by isomeric
transition.
Isomeric transition (cont’d)
99m-Tc can be “built” into many molecules
This allows for imaging many different organs
e.g.,
MIBI scan (cardiac)
HIDA scan (hepatobiliary)
MAG3, DTPA (renal)
Interactions of radioactive
emissions with matter
- Important for understanding medical applications of
radioactivity - Important for understanding how radiation is detected
- Important for understanding the effect of radiation on living
systems - Important for designing and using radiation protection
- Must consider particle interactions and electromagnetic
interactions separately.
𝝰-particles cause ionization of targets (mostly);
this produces the ion pair
α-particle (7 MeV) linear range
Material Penetration (µm)
Air 59,000
Water (tissue) 74
Copper 14
Lead 2
So talked very briefly about this. I’m not going to trouble you with the Ion pair. This is very interesting info. The take on points is that one alpha particle
it? By the time it loses all its energy it can.
This is just to give you an idea of the impact that can produce 2,000 200,000ion pairs. Why, that’s important is because
when we talked about radiation, and especially this form of ionizing radiation. This is what’s meant by ionizing right. It’s ionizing a target. This could be on the protein on lipid on DNA. It’s ionizing it, and it can keep on doing this, and in a well well defined range
until that alpha particle runs out of juice.
the juice is energy when it runs out of its kinetic energy, and it’s sort of ionizing potential. Then it it just will then stop. So that takes a while.
But how far do alpha particles go? I gave you this example of it sitting on the projector. And how worried I should be! It doesn’t travel too far. So that is kind of an advantage
and a disadvantage. If you’re talking about Zofigo.
the drug. if you can get it
to right by the bone metastases, because it’s like calcium, and just release all its energy there, or concentrated there. Then it’s a good thing.
but it’s not a good thing if it’s just being. This goes throughout the body like the case of polonium.
which is not targeted. It’s just this big dose flooding going all over the place making
someone’s sick
So if you think about tissue.
it’s a it’s kind of a short range.
Okay, and things like metals and all that are well known to stop.
Charged Particle Interactions
-particle interactions (excitation and ionization)
β
-
-particles do not travel in a straight line and travel further than -
particles
β
+
-particle interactions (Positron annihilation).
1. loses kinetic energy; 2. meets an e-
; 3. antimatter+matter rxn
(massenergy).
penetration is a little less, and the energy is a little less overall.
So that’s sort of one thing to keep in mind in terms of a hazard.
is, it’s sort of a medium kind of hazard
So there there is some utility
to using it
in terms of delivering a directed dose. If that’s the case, the similar, the sort of the anti matter of the beta minus particle is the beta plus particle the positron. And then, in fact, this is a an antimatter, not a reaction that takes place in PET imaging
because the beta plus pull somewhere along the lines interact with its opposite counterpart.
the electron, and they annihilate each other. Their masses
disintegrate masses. It’s converted to energy. It’s a very interesting neat reaction of a matter matter antimatter reaction.
• this produces gamma rays.
• So this is the why PET imaging is kind of can be used because you you talk about PET imaging you’re actually looking at gamma rays.
β
+
-particle interactions (Positron Emission Tomography (PET).
The positrons from internally targeted
radioactive drugs are detected via
their gamma rays by specialized
cameras to give 3D pet images
Electromagnetic Radiation Interactions
Gamma rays (g) and x-rays
Photons described by their wavelength and their frequency (cycles per
second; ) = c/ (c = speed of light)
Gamma rays and x-rays have the same character as light, uv and ir radiation
but have higher energies.
Energies for x-rays are generally lower than for gamma rays but they overlap.
E = h (h = Planck’s Constant)
These photons are very penetrating and are the main reason that lead
and other dense shielding is used where radiopharmaceuticals are
prepared or used.
Nucleus can eliminate excess energy by photon emission.
Photon emission can occur during decay modes
Photons are mono-energetic.
Two types of interactions are of x-ray and g-rays are important with regard to
radiopharmaceuticals.
Hazards?
*Complex issue – Radiation
Health Physics.
*Particularly complex with
internal radioactivity.
*Related to ionization in
tissues.
*Related to specific
ionization of various
emissions.
