1- radiation physics

definition of radiation

energy in transit

definition of ionization

removal of electrons from an atom → formation of an "ion pair”

what are orbitals

3D shapes of where electrons exist around a nucleus

what are the 6 types of orbitals

S, P, D, F, G, H

what’s the Z number of a nucleus

atomic # aka # of protons (P)

# of electrons in a neutral atom equals what

Z number

what’s A number of a nucleus

# of protons (P) + N

what’s electron binding energy

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

what’s the relationship between Z number + electron binding energy

direct relationship

definition of electromagnetic radiation

movement of energy through space as a combination of electric + magnetic fields

7 types of electromagnetic radiation

1. gamma rays

2. x-rays

3. ultraviolet

4. visible light

5. infrared

6. microwaves

7. radio waves

what’s quantum theory

energy transfer in the form of “bundles” (or packets) of energy called photons (or “quanta”)

mass + charge of x-rays

no mass or charge

x-rays travel in zigzag or straight lines

straight

x-rays’ ability to ionize allows them to do what 2 things

1. affect photographic film

2. produce biological + chemical changes

x-rays’ range of wavelength

0.1 A to 0.5 A (1 A = 1/10 nm)

2 mechanisms of x-ray production

1. Bremsstrahlung: electron → nucleus interaction

2. characteristic radiation: electron → electron interaction

describe the Bremsstrahlung mechanism

high energy electron is decelerated by nuclei of high Z # material→ kinetic energy of high energy electron is converted into photon → x-ray is generated

describe the characteristic radiation mechanism

high energy electron interacts w/ an inner shell electron + knocks it out of orbit → its vacancy is filled w/ an outer shell electron→ difference in energy level between outer + inner shell is released via x-ray photon

which mechanism is the primary source of radiation in the x-ray tube

Bremsstrahlung

describe each part of the x-ray tube and how it facilitates the 2 mechanisms

1. cathode: electron source

2. focussing cup: concentration of electrons

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

4. anode: target to stop electrons

how does the cathode emit electrons

current heats up the cathode abt 2200^o C → electrons emitted → formation of electron cloud

4 qualities of tungsten that make it a great anode

1. High atomic number

2. High melting point

3. Low vapor pressure ( to maintain vacuum)

4. High degree of thermal conductivity

6 factors that control the x-ray beam

1. tube voltage (kVp)

2. exposure time (S)

3. tube current (mA)

4. filtration

5. collimation

6. distance of x-ray tube from pt/receptor

what does the highest point + lowest point of each curve represent

• peak: mean photon energy (keV)

• end of curve: KvP at which the x-ray beam was acquired

increasing kVp results in what

number of photons (keV) + max energy of the beam increases

describe how filtration affects the x-ray beam

removal of low energy photons from the x-ray beam → reduces patient risk + intensity of beam, therefore compensatory increase in exposure time needed

which components of the x-ray tube provide filtration

• inherent filtration via glass, oil

• added filtration via aluminum disk

what are the regulated required amounts of filtration for certain doses

• 50-70 kVp: 1.5 mm aluminum

• above 70 kVp: 2.5 mm aluminum

describe the relationship between tube current (mA) + photon energy

higher the current (mA) → higher number of photons

describe the relationship between exposure time + photon energy

longer exposure → higher number of photons

describe how collimation affects the x-ray beam

• reduces size + modifies shape of beam

• reduces volume of tissue irradiated

• improves image quality

describe how distance from x-ray tube affects the x-ray beam

inverse square law: I (intensity) = 1/D² (distance)

3 types of x-ray interaction w/ matter

1. coherent scattering

2. photoelectric effect

3. Compton scattering

what’s the photoelectric effect

how images are formed:

photon collides w/ inner-shell electron → electron is ejected (ionization) → photon transfers all energy to the electron + photon ceases to exist → another electron from higher energy fills the vacancy → radiation is emitted

how is the photoelectric effect clinically significant

Z of bone is higher than Z of soft tissue → differential photoelectric absorption within different types of tissues makes production of a radiographic image possible

anything on the x-ray that’s black: received photons vs. white: no photons

what’s Compton scattering

photon interacts w/ outer orbital electron → electron ejected from target atom → photon is deflected as a scatter photon w/ lower energy

each type of x-ray interaction makes up what % of interaction in an x-ray beam

1. coherent scattering: 7%

2. photoelectric effect: 27%

3. Compton scattering: 57%

definition of equivalent dose

measure of comparison of biological effectiveness of different types of radiation (Sievert, Sv)

definition of effective dose

estimates risk in humans by comparing different exposures, considering radiosensitivity of tissues + biologic effectiveness (Sievert, Sv)

7 types of ionizing radiation

1. x-ray

2. gamma ray

3. neutrons

4. beta particles

5. alpha particles

6. protons

7. heavy ions

2 mechanisms of radiation-induced cell injury

1. direct effect

2. indirect effect

which mechanism is responsible for 2/3 of radiation-induced biologic damage

indirect

describe the mechanism of direct effect radiation-induced injury

ionization of biologic macromolecules directly by a photon of ionizing radiation

describe the mechanism of indirect effect radiation-induced injury

1. water in tissues absorbs photon → ionization of water to form free radicals (radiolysis of water)

2. free radicals interact w/ macromolecules → biologic changes

what’s the primary target for cell damage from radiation

DNA, at risk for double-strand + single strand break

2 types of radiation injury

1. tissue rxns (deterministic effects): large # of cells killed → erythema, cataract formation

2. stochastic effects: sublethal damage to cells → carcinogenesis or heritable mutation

which type of radiation injury’s severity is independent of dosage

stochastic effects

2 factors that influence radiation damage

1. host: radiosensitivity of cell/tissue, stage in cell cycle, reproductive capability, age, O₂ + temp (higher = greater damage), volume of tissue

2. radiation: type of radiation/LET (higher LET = more damage), dose, dose rate

the most radiosensitive cells have which 3 characteristics

Law of Bergonie + Tribondeau:

1. have high mitotic rate (actively proliferating)

2. undergo many future mitoses (younger cells)

3. undifferentiated/non-specialized in structure + function (immature cells)

what’s an exception to the Law of Bergonie + Tribondeau

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

rank organs/tissue types from most → least sensitive to radiation

1. bone marrow (lymphoblasts, lymphocytes, plasma cells, erythroblasts), intestines (epithelial stem cells), oral mucous membrane (basal cells), spermatogenic cells

2. skin + other organs w/ epithelial linings, inner enamel epithelium

3. fine vasculature

4. salivary glands, kidneys, liver, pancreas

5. muscles (striated muscle cells), brain (neurons), spinal chord, erythrocytes

2 major effects of radiation on embryo/fetus

1. teratogenic effects (deterministic): death in 1st week of pregnancy, intra-uterine growth retardation, congenital malformations, developmental abnormalities

2. stochastic: childhood cancer

2 factors influencing probability of radiation effects on embryo

1. dose

2. stage of gestation @ time of exposure

radiogenic effects for an embryo 0-9 days old

all or none

radiogenic effects for an embryo 10 days-6 weeks old

congenital anomalies + growth retardation

radiogenic effects for an embryo 6-40 weeks old

1. growth retardation

2. microcephaly

3. mental retardation

dose threshold of radiation to the fetus required to produce birth defects

100-250 mSv

4 acute radiation syndromes + their dosages

1. prodromal syndromes: 1-2 Gy

2. hematopoietic syndrom: 2-7 Gy

3. GI syndrome: 7-15 Gy

4. CNS syndrome: 50 Gy

radiation therapy is used in the oral cavity for what

malignant oral lesions that are radiosensitive

dosage for radiation therapy to oral cavity

total 64-70 Gy in 6-7 weeks

5 structures in the oral cavity that can be affected by radiation therapy

1. oral mucous membrane

2. taste buds

3. teeth

4. salivary glands

5. bone

which oral cavity structures can heal from radiation therapy

1. oral mucous membrane: after 2 months

2. taste buds: after 60-120 days

describe the effect of radiation therapy on the oral mucous membrane

• desquamation

• inflammation/pain

• white/yellow pseudomembrane

• secondary fungal infections

• long term: atrophic, thin, avascular mucosa

describe the effect of radiation therapy on taste buds

lowered taste acquity

describe the effect of radiation therapy on teeth

• tooth bud destroyed

• malformations, arrested growth

T/F: erupted teeth are radioresistant (resistant to irradiation)

true

describe the effect of radiation therapy on salivary glands

• xerostomia

• pH altered → decalcificaition of enamel

• radiation caries

describe the effect of radiation therapy on bone of the oral cavity

osteoradionecrosis: damage to vasculature of periosteum + cortical bone, destruction of osteoblasts