ORAD800: Radiation Biology

Radiation Biology

The study of the effects of particulate and electromagnetic radiation including ionizing radiation, on living systems

Ionizing Radiation include ___ & ___radiation

particular

electromagnetic

What causes the majority of Radiation Exposure?

Radon & Thoron (37%)

X-Ray and Gamma-Rays are able to remove ____ from atoms causing __

electrons

Ionization

Unit of Measurement for Exposure

Roentgen (R)

Roentgen(R) measures?

Exposure

Absorbed Dose

radiation absorbed dose (rad)

Radiation Absorbed Dose (Rad) measures?

absorbed dose

1 Gray (Gy) =

100 rads

Effective Dose (sV)

means of expressing the radiation -induced risk to the whole body even though the whole body was not exposued

The Effective Dose (sV) is the sum of the products of the ___ to each ___ and ___

equivalent dose

Each tissue/organ

tissue weighing factor

Tissue Weighing Factor

risk factor of an organ

Cells are most sensitive at or near __

mitosis

___ is the most resistant cell phase

Late S

Direct Action

direct ionization of DNA molecule --> Genetic Damage

Indirect Action

radiation causes ionization of water- free radicals --> target DNA

Which Action is responsible for 2/3 of Damage?

Indirect

Indirect Action is responsible for ___ damage

2/3

Sensitivity varies directly with

-rate of ___

- number of __

proliferation

future divisions

Sensitivity varies Indirectly with

-degree of ___

differentiation

Free Radical DNA Damage Consequences

Repair

Death

Genetic Alterations

Carcinogenesis

Event Sequence in Radiation Injury

Absorption of Radiation

Excitation/ Ionization

Chemical Alteration

Enzymatic Repair Development of Lesion

Low Dose Effects

cell mutation

cancer induction

in-utero effects

High Dose Effects

cell killing

tissue/organ effects

whole body effects

Stochastic Effects where the ___ is proportional to the dose

risk

Stochastic Effect severity is ___ of the dose

independent

Deterministic Effects where the ___ is proportional to the dose

severity

What is the area of uncertainty for Radiation Carcinogenesis?

low doses if they --> incidence of tumors

Gametic Mutation

germline

Somatic Mutation

somatic cells

What is the consequence of Somatic Mutations?

cancer induction

Law of Bergonie & Tribondeau

Most Sensitivit Cells are those that:

-have a high ___

- undergo many ___

- are primitive in ___

mitotic rate

future mitoses

differentiation (not small lymph and oocyetes)

What very sensitive?

Bone Marrow (high proliferation)

What is the least sensitive?

Nerve Cells

Linear Energy Transfer (LET)

average energy released from ionization and excitation to absorbing medium per unit track length (keV/um)

X-Rays have ___ LET

low (~1 keV/um)

What has a low LET?

X-rays

Alpha Particles/ Neutrons have ___ LET

high (~100 keV/um)

What has a high LET?

Alpha Particles/ Neutrons

Factors Influencing Radiation Induced Cancer

radiation dose/ dose rate

LET (radiation quality)

gender

age

T/F: There is no risk of fetal death, malformation, growth retardation or impairment of mental facility in Dental X-rays

TRUE

dose to fetus is indistinguishable from background radiation

Maximum Permissible Dose (MPD)

the amount of radiation that an individual is allowed to receive from artificial sources of radiation, such as X-ray machines

- occupation, non

MPD of whole body

50

MPD of skin

150

MPD of organs and organ systems

500

MPD of pregnant women

5 (gestation)

0.5 (dose limit in 1 month)

As Low As Reasonably Achievable (ALARA)

every measure that will taken to assure that exposed persons will receive the smallest amount of radiation possible

T/F: Radiographs should be taken every 6 months

False

T/F: Take a full mouth series or PA on every new patient

False

T/F: No routine radiographs. Radiographs should be taken only after considering patients history and clinical findings

True

What kVp is optimal?

70-90

What is the optimal filtration?

1.5 - 2.5 mL

Infection Control of taking X-rays

protective apparel

surface asepsis

surface covers