Radiation Physics and Biology

what is energy in transit called?

radiation

what is the removal of electrons from an atom resulting in the formation of an ‘ion pair’ called?

ionization

what is the the attractive force that keeps electrons bound to the nucleus in their orbitals?

electron binding energy

what is the relationship between Z # and binding energy?

higher Z # = higher binding energy

what are characteristics of neutrons?

• no charge (neutral)

• mass is approx same as proton (1.68 × 10^-24 g)

what is Z-number?

• # of protons (aka atomic #)

  • in a neutral atom, # of protons = # of electrons

• determines the identity of an element

what is A-number?

# of protons + neutrons (aka atomic mass #)

what does the quantum theory suggest?

energy transfer in the form of “bundles” (or packets) of energy called photons (or “quanta”) that move at the speed of light and w a specific amount of energy

what are some important properties of x-rays?

• no mass

• no electric charge

• travel in waves

• travel w specific frequency (speed of light)

• highly penetrating

• travel in straight lines (diverging from central focus)

• able to ionize

  • affect photographic film

  • able to produce biological/chemical changes

  • range of wavelengths (0.1A to 0.5A)

what are the 2 mechanisms of X-ray production?

1. Bremsstrahlung (electron to nucleus interaction)

2. characteristic radiation (electron to electron interaction)

of the 2 mechanisms of x-ray production, which is the primary source of radiation generated by an x-ray tube?

Bremsstrahlung mechanism

describe how the Bremsstrahlung mechanism produces x-ray.

X rays are produced when high velocity electrons are suddenly decelerated when they pass close to or directly hits the nuclei of high Z # absorbing material.

what types of xray photons are produced via bremsstrahlung mechanis?

photons w varying energy levels (within a specific range)

describe how the characteristic mechanism produces x-ray.

X rays are produced when high velocity electrons interact with an inner shell electron and knocks it out of the orbit. This vacancy( gap) is filled out by an outer shell electron. The difference in the energy levels is released and an x-ray photon

what types of xray photons are produced via characteristic mechanism?

photons with specific energy level that is characteristic of the atom produced

of the 2 mechanisms of x-ray production, which contributes a small fraction of photons in the beam?

characteristic mechanism

what are the key components of xray generating tubes?

1. electron source (cathode)

2. concentration of electrons (focussing cup)

3. mechanism to accelerate electrons (potential difference or tube voltage kVp)

4. suitable target to stop electrons (anode)

describe the process of thermionic emission.

what are the 2 components that make up the anode of a xray tube ?

• tungsten target

• copper stem (good thermal conductor)

why is tungsten a good anode target?

• high atomic #

• high melting point

• low vapor pressure

• high degree of thermal conductivity

22

in an x-ray generating tube, what material makes up the anode vs cathode?

• cathode → tungsten filament

• anode (tungsten targe in a copper block)

Movement of energy through space as a combination of electric and magnetic fields is referred to as…?

electromagnetic radiation (gamme rays, x-rays, ultraviolet, visible light, infrared, microwaves, radio waves)

what category of organs and cells are MOST sensitive to radiation (highest radiosensitivity)?

• Bone marrow (lymphoblasts, lymphocytes, plasma cells, erythroblasts)

• intestines (epithelial stem cells)

• oral mucous membrane (basal cells )

• Spermatogenic cells

what cell types are an exception to the law of Bergonie and Tribondeau?

small lymphocytes & oocytes (mature in differentiation yet sensitive to radiation)

what are the teratogenic effects (deterministic, safe doses) of radiation on an embryo/fetus?

• intrauterine death (1st week of pregnancy)

• intra-uterine growth retardation

• congenital malformations

• developmental abnormalities

what are the stochastic effects (no safe dose) of radiation on an embryo/fetus?

cancer in childhood

what factors influence the probability of radiation effecting an embryo?

• dose to embryo/fetus

• stage of gestation at time of exposure

A dose threshold of ______ to the fetus is required to produce x-ray induced birth defects

100-250 mSv

This is orders of magnitude above the fetal dose from dental radiographs (<.01 mSv)

what are possible radiogenic effects at a gestational age of 0-9 days (preimplantation stage) ?

all or none

what are possible radiogenic effects at a gestational age of 10 days - 6 weeks (organogensis stage) ?

congenital anomalies, growth retardation

what are possible radiogenic effects at a gestational age of 6-40 weeks (fetal stage) ?

growth retardation, microcephaly, mental retardation

t/f: Risk of Stochastic effects (childhood cancer/ genetic mutation) occur throughout pregnancy

true

acute radiation syndromes occur usuaully as a result of…?

whole body irradiation (accidental, nuclear plant disasters, etc.) → never happens any other way

acute radiation syndromes are ___-dependent.

dose

• Prodromal symptoms (1-2 Gy)

• Hematopoietic syndrome (2-7Gy)

• Gastrointestinal syndrome(7-15Gy)

• Central nervous system syndrome (50Gy)

acute radiation syndrome: prodromal symptoms

• dose?

• time of onset?

• manifestation?

• dose: 1-2 Gy

• time of onset: minutes-hours after exposure

• manifestation: anorexia, nausea, vomiting, fatigue

acute radiation syndrome: hematopoietic symptoms

• dose?

• time of onset?

• organs affected?

• manifestation?

• dose: 2-7 Gy

• time of onset: days to months

• organs affected: hematopoietic stem cells in bone marrow and spleen

• manifestation: infection, hemorrhage, anemia (death 10-30 days)

acute radiation syndrome: gastrointestinal symptoms

• dose?

• time of onset?

• organs affected?

• manifestation?

• dose: 7-15 Gy

• time of onset: few weeks to months

• organs affected: small intestine

• manifestation: nausea, vomiting, diarrhea, electrolyte imbalance, circualtory collapse (death 3-10 days)

acute radiation syndrome: cardiovascular and CNS symptoms

• dose?

• time of onset?

• organs affected?

• manifestation?

• dose: 50 Gy

• time of onset: death in 1-2 days

• organs affected: brain

• manifestation: lethargy, tremors, convulsions, ataxia, coma

radiation therapy in the oral cavity is used to target malignant oral lesions that are radiosensitive. what is the total dose used?

64-70 Gy in 6-7 weeks

how does radiation affect salivary glands?

• radiation caries

• reduced secretion (xerostomia)

• pH altered (decalcification of enamel)

how does radiation affect taste buds?

• decrease taste acquity

• recovery to almost normal 60-120 days post irradiation

how does radiation affect teeth? (pre-calcification vs post-calcification vs post-eruption)

• prior to calcification → tooth bud destroyed

• post calcification → malformations, arrested growth

• erupted teeth → radioresistant

• severity is dose dependent

how does radiation affect bone?

osteoradionecrosis

• damage to vasculature of periosteum, cortical bone

• destruction of osteoblasts