Angela's Radiation therapy Flashcards
What is an alpha particle?
Two protons and two neutrons (+ charge) emitted from the nucleus during a form of radioactive decay, called alpha-decay. An alpha-particle is identical to the nucleus of a normal helium atom.
“An alpha man is full of helium”
What is a beta particle?
Single electron (- charge) - high energy, high speed electrons (β-) that are ejected from the nucleus, [Can also form a positron (β+).
What is the penetrance of a beta particle?
None - it is stopped by sheets of aluminum or a few mm of tissue.
What is a gamma particle?
Gamma particle is a photon (a unit of electromagnetic energy), that is emitted by the nucleus of some radionuclides following radioactive decay. Gamma photons are the most energetic photons in the electromagnetic spectrum.
High enerG - G - gamma
What is an X ray?
A penetrating form of high-energy electromagnetic radiation. An X-ray is a packet of electromagnetic energy (photon). X-rays are produced by electrons external to the nucleus.
Where do x-rays originate?
OUTSIDE the nucleus - from the electron cloud of an atom. This is generally caused by energy changes in an electron, which moves from a higher energy level to a lower one, causing the excess energy to be released.
How are X-rays produced?
X-rays are commonly produced in X-ray tubes by accelerating electrons through a potential difference (a voltage drop) and directing them onto a target material (i.e. tungsten).
What are properties of alpha particles?
Alpha particles are highly ionising because of their double positive charge, large mass, and because they are relatively slow. They can cause multiple ionisations within a very small distance. This gives them the potential to do much more biological damage for the same amount of deposited energy. They are unable to penetrate very far through matter and are brought to rest by a few centimetres of air or less than a tenth of a millimetre of biological tissue.
What is a proton?
Large, positively charged elementary particle. Created by by ionization of a hydrogen atom - stripping an electron from a hydrogen atom via acceleration at 300MeV energies.
Sport Pros stay HYDRidated. Protons are from hydrogens
What is a neutron?
Large, neutral elementary particle.
How are neutrons produced?
Neutrons are produced when alpha particles are accelerated at and hit any of several light isotopes including isotopes of beryllium, carbon, or oxygen. Also can be produced by fission.
What is a pi meson (pion)?
Any of three subatomic particles: π0, π+, and π−
Each pion consists of a quark and an antiquark. They are unstable, decaying after a short lifetime. Neutral pions generally decay into gamma rays.
What is the clinical application of the photoelectric effect?
Diagnostic radiology
Is the photoelectric effect dependent on atomic number?
Yes, Z^3
(Z is the atomic number)
What radiologic phenomenon starts to occur at 1.02 meV?
Pair production (becomes dominant at 30 MeV)
Pair production is the production of a particle-antiparticle pair from the decay of a neutral particle or from a pulse of electromagnetic energy traveling through matter. The most commonly observed pair-production process is the materialization of an electron and a positron from a high-energy photon.
At energies greater than 30 MeV, pair production is the dominant mechanism of radiation interaction with matter. As photon energy increases, the dominant interaction mechanism shifts from photoelectric effect to Compton scattering to pair production.
Is pair production dependent on atomic number?
Yes
PP is related to the atomic number (Z) of attenuator, incident photon energy (E) and physical density (p) by Z E (- 1.022) p.
What is the Compton Effect?
The Compton effect (also called Compton scattering) is the result of a high-energy photon (X-ray or gamma ray) colliding with a target, which releases loosely bound electrons from the outer shell of the atom or molecule. The scattered radiation experiences a wavelength shift
“The Compton family is Phony” To remember PHOtones.
NOT related to Z (atomic number) but density of tissue (penetrates 0.5-3cm)
What is the clinical application of the Compton Effect?
Radiotherapy
What is the particle in the Compton Effect that interacts with DNA directly and H2O to form hydroxy free radicals?
Displaced electron
At what energy does the Compton Effect predominate in tissue?
~25 keV to 25 MeV
Most radiation treatments are performed at energy levels of about 6-20 MeV
keV is 1000 times smaller than a MeV
In the Compton effect, what does the incident photon interact with?
Loosely bound outer orbital electrons
In the Compton effect, what is % of damage to DNA is caused directly from the interaction of the photon with DNA
direct DNA interaction - responsible for 25% of damage due to radiation. The other 75% is caused by indirect action (the photon creating incidental free radicals when go on to cause DNA damage
In the Compton effect, what is indirect action? (ie how much DNA damage is not caused by the direct interaction of the electron with DNA)
Formation of free hydroxy radicals - responsible for 75% of damage due to radiation
Most DNA damage is induced indirectly by free radicals
In Compton Effect, is absorption dependent on tissue density or atomic number?
Not dependent on atomic number; is dependent on tissue density because Tissue density is correlated with electron density for biological tissues
Compton scatter is dependent on the number of available electrons; the electron density of the material; and on the physical density but not on the atomic number of the material.
The probability of a Compton interaction is directly proportional to the electron density of the absorber. The density of electrons in bone (5.55 × 1023/cm3) is greater than in soft tissue (3.34 × 1023/cm3); therefore the probability of Compton scattering is correspondingly greater in bone than in tissue.
At what energy range does the photoelectric effect predominates in tissue?
10-25 keV
keV is 1000 times smaller than a MeV
What are the most common sources of radiation for brachytherapy in GYN cancers?
Cesium-137 (half-life 30 years)
Iridium-192 (half-life 74 days)
What is Linear Energy Transfer (LET)?
The average amount of energy that is lost per unit path-length as a charged particle travels through a given material
What has high LET?
Densely ionizing radiation like neutrons, alpha particles, pi-mesons
What has low LET?
Sparsely ionizing radiation like gamma rays and X-rays, beta particles/high-energy electrons, photons, Protons
What are the benefits of high LET energy?
More effective in hypoxic tissue (necrotic tumor)
What has the highest LET?
Neutrons (more than protons, pi mesons, X-rays, photons). Carbons are also high LET sources.
Alpha > neutron if this is an answer
What has the lowest LET?
X-rays (250 keV)
What does increased oxygen do to the shoulder of the cell survival curve?
Shifts it to the left
Normal tissue tolerance for radiation (TD5 and TD50) for the following organs:
Bone marrow:
Kidney:
Liver:
Small intestine:
Spinal cord:
Large intestine:
Bladder:
Rectum:
Vagina:
Skin:
Stomach:
Bone marrow: Aplasia 250/450, Pancytopenia 3000/4000
Kidney: 1500/2000
Liver: 3000/4000
Small intestine: 4000/xx
Spinal cord: 4500/5500
Large intestine: 4500/xx
Bladder: 6000/8000
Rectum: 6000/8000
Vagina: 8000-8500/xx
Skin: 5000/xx
Stomach: 5000/xx
