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24 Cards in this Set

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What is ionizing radiation?

Define ionization event.

Which EM waves exhibit this?
Propagation of EM wave/particle with sufficient energy to result in IONIZATION EVENT--detach an electron from an atom

Gamma, x-rays
Photon vs Particle:
Define
Examples
Photon:
High energy, ionizing EM rays composed of energy packets w/o mass

Ex: x-rays (extranuclear origin), gamma-rays (originate from within nucleus)

Particle:
Small fast-moving particles with energy and mass
Ex: Protons, electrons, beta particles, neutrons, alpha particles
What is directly ionizing radiation?
Examples.
Particle directly disrupts atomic structure of the absorber and alters chemical properties.

Ionization caused by charged particle (electrons, protons, alpha particles, beta particles)
What is indirectly ionizing radiation?
Examples.
Indirect disruption of atomic structure of absorber by colliding with orbit electron/nucleus of charged particle.

Ex: x-rays, gamma-rays, neutrons
Photons vs Neutrons:
Methods of ionization
Photons (X-rays, gamma-rays):
Generate fast moving electron in electron shell

Neutron:
Collide with nucleus
Gray (Gy): what does it measure?
measures absorbed dose of radiation; used to define dose of radiation
Becquerel (Bq): what does it measure?
measures activity of radioactive material; determines strength of radioactive substance
Sievert (Sv): what does it measure?
radiation dose equivalent ; defines radiation dose for radiation safety
What two effects are the most crucial to the interaction of photons with matter?
Photoelectric effect
Compton effect
Compton vs Photoelectric Interactions:
Energy (Low/High)
Dependence on Z
Diagnostic vs Therapeutic
Compton:
Higher energy (MV)
Independent of Z
Therapeutic

Photoelectric:
Lower energy (KV) photon
images (like for x-rays)
Z^3
Diagnostic
Critical injury to DNA in radiation therapy.
dsbreaks
Indirect vs Direct Damage:
General
Which is more common?
Indirect more common; result of electrons interacting with water (Free radicals form).

Direct: Ionized electron directly interacts w/DNA
OH radical is seen in (indirect/direct damage)
Indirect
How does DNA damage result in cell death?
dsbreak-->cell attempts mitosis and can't complete it. dies.

OR

dsbreak-->downstream signaling-->apoptosis
Radiation kills the same _____ of cells every time.
Radiation kills same fraction of cells every time (percentage, not number! ex: kills 50% of cells it hits)

In theory, you can never kill all tumor cells. Never reach 0.
Define each R--
4 R's for Interaction of Radiation with Cell Population:
Repair
Redistribution
Repopulation
Reoxygenation
Repair: Not all cells damaged by radiation die, some undergo DNA repair

Redistribution:
Different portions of cell cycle have different vulnerabilities to radiation.

Repopulation: cells can proliferate during/between doses of radiation and may respond to death of adjacent cells by increasing their proliferation rate (accelerated repopulation)

Reoxygenation: for x-ray (sparsely ionizing) radiation, oxygen essential for DNA damage. O2 binds DNA radical and prevents DNA damage repair. (Note: Thiols are radical scavengers and can undo damage done by radiation)
If not all cells die from dsbreaks, how do they go on to divide?
Recombinational repair fixes dsbreaks:

Homologous recombination: Sister chromatid used as template; high fidelity
Which phases of the cell cycle are most vulnerable to radiation?

Least vulnerable?
G1/S, G2/M = highly radiosensitive

Late S = highly radioresistant (where all replication and repair takes place)
What effect do hypoxic conditions have on radiation therapies?

Factor by which calculate new dose?
Hypoxia (O2 needed to maintain DNA damage and not have it be reversed by thiols)-->need greater dose of radiation

For x-rays, need to increase dose by 3 times!!
Acute responding tissues:
What are they?
Examples?
Tissues with short, rapid cell turnover. Respond to radiation like tumors. Stem cells repopulate post-tx and pts recuperate readily within weeks.

Ex:
Gut
Skin
BM
Mucosa
Late-Responding Tissues:
What are they?
Examples?
Tissues with slow, prolonged cell turnover. Tend to repair radiation damage relatively well. If damaged, injury can be severe and irreversible and doesn't manifest for months to years.

Ex:
Brain
SC
SQ tissues
Kidney
Lung
Bladder
What is dose fractionation? Advantages?
Divide dose into number of small fractions to spare normal tissue.

Allows for repair of sublethal damage (to normal cells) between doses, ACCELERATED repopuln of normal cells.

AND

Increases damage to tumor via reoxygenation and redistribution
Effect of dose fractionation on hypoxic tumor cells.
Fraction of irradiation will likely oxygenate tumor cells and result in more effective killing upon next dose.
What drugs does radiation interact with?
Alkylating agents (enhances effect)

5-FU (anti-purine?)--interferes with DNA damage repair

ANYTHING THAT AFFECTS CELL CYCLE, MT's, DNA, etc.