Biological Effects of Radiation (CTBC 22) Flashcards
When an x-ray enters matter (e.g., human tissue), there are 4 things that can happen:
Transmission
Coherent scattering
Photelectric absorption
Compton scattering
During a CT exposure _______ of x-ray photons pass through the patient
billions
When x-rays pass through the body without interacting in any way
Transmission (these x-rays aren’t absorbed/scattered, but are measured by the detector array)
An x-ray photon absorbed by an electron then immediately emitted from the electron with all its original energy describes
Coherent scattering: these don’t result in ionization/biological harm to the patient, but are “scattered” in a different direction than the original path
Non-Ionizing Interactions (2)
Transmission
Coherent Scattering
Ionizing Interactions (2)
Photoelectric Absorption
Compton Scattering
The removal of a bound electron from an atom
Ionization (the creation of charged particles): results in broken molecules and damaged cells
Ionization which occurs when an electron is ejected out of its orbit by fully absorbing an incoming x-ray photon
Photoeletric absorption
Ionization which occurs when an electron is ejected out of its orbit by partially absorbing an incoming x-ray photon, resulting in a (residual) scattered x-ray photon
Compton Scatter
Decrease in x-ray beam intensity d/t interactions with matter
Attenuation
Increasing kVp _______ attenuation and (usually) _______ patient dose
Decreases: increased x-ray energy decreases probability of attenuation
Increases
Ionization breaks chemical bonds, which may lead to a cascade of
additional ionizations and broken molecules, possibly damaging the cell
Ionizing radiation of cells may result in (3)
Cell will not repair itself and die
Cell will repair itself completely w/no lasting consequences
Cell will repair itself incompletely/incorrectly w/possible mutation/cancer/death
When ionizing radiation causes a cell to repair its DNA incompletely/incorrectly, a mutation might occur resulting in
Cancer and eventually death
Cataract formation and radiation-induced miscarriage are examples of
Deterministic effects of significant cell death
Heritable diseases and cancer are examples of
Probabilistic effects of significant cell mutation
_______ effects occur only at specific doses of radiation and not before
Deterministic
When the dose-response threshold is determined/known, the severity of the effect _______ with increasing dose
Increases
Deterministic effects of radiation are usually relevant only to
Very high doses of radiation
Deterministic level for radiation-induced miscarriage
100 mGy (pre-implantation)
Deterministic level for decreased sperm count
150 mGy
Deterministic level for cataract formation
2000 mGy
Deterministic level for Erythema (skin redness)
2000 mGy
Deterministic level for Epilation (hair loss)
3000 mGy
Most common radiation-induced cancers (6)
Leukemia
Thyroid
Breast
Lung
Bone
Skin
Effects based on (random) chance, not a minimum dose
Stochastic effects: Theoretically any radiation dose increases the chance of a stochastic effect
Any dose of radiation could cause cancer/the risk of acquiring cancer increases as dose increases
Linear Non-threshold (LNT) model of the probability of radiation-induced cancer
