1. Radiation physics and biology part 3

definition: study of effects of ionizing radiation on living systems

radiation bio

which two types of ionizing radiation are uncharged, non-particulate (electromagnetic)?

X-ray Ɣ-ray

which type of ionizing radiation is uncharged, particulate?

n

which types of ionizing radiation are charged, particulates?

beta particles, alpha particles, protons, heavy ions

how does radiation injury/damage occur?

result of ionizations w/in tissues and/or cells

what are the two mechanisms of radiation induced-cell injury?

direct and indirect effect

definition: ionization of biological macromolecules DIRECTLY by a photon of ionizing radiation

direct effect, break chemical bonds

which mechanism of radiation induced cell injury occurs 1/3rd of the time?

direct effect

which mechanism of radiation induced cell injury occurs majority of the time?

indirect effect

describe indirect effect mechanism

radiation ionizes water and causes hydrolysis which leads to free radicals which then interact with macromolecules to produce biologic changes

what are the four radiation injury outcomes?

DNA damage:

• DNA ds break: cell death, mutations, carcinogenesis

• DNA ss

• changes in proteins, lipids, carbs

what are the two types of radiation injury?

• tissue reactions/deterministic effects

• stochastic effects

definition: radiation injury to organisms resulting from killing large number of cells

tissue reactions/deterministic

which type of radiation injury: erythema, cataract formation

tissue reactions/deterministic

definition: sublethal damage by radiation to individual cells leading to carcinogenesis or heritable mutation

stochastic effect

which type of radiation injury: carcinogenesis or heritable mutation

stochastic effect

is there a threshold dose for deterministic effects/tissue rxns

yes! there is a dose above which an effect is seen

is there a threshold dose for stochastic effects?

NO! assume there is no safe dose bc any single photon is capable of causing changes in DNA leading to cancer or genetic effects

is deterministic effects/tissue rxns severity dose dependent?

yes, proportional but probability is only above threshold dose

is stochastic effects severity dose dependent?

no, independent but the greater those dose the greater chance for having an effect

what are the seven host factors that influence radiation damage?

• radiosensitivity of cell/tissue

• stage in cell cycle

• reproductive capability

• age

• O₂

• temp

• volume of tissue (H₂O free radicals)

what are the three radiation factors that influence radiation damage?

• type of radiation/LET (high LET = more damage)

• dose

• dose rate

three principles of the Law of Bergonie and Tribondeau

the most radiosensitive cells (most prone to harmful radiation effects) are those that:

• have high mitotic rate = active prolif

• undergo many future mitoses aka younger cells

• undifferentiated/non-specialized in structure and function = immature cells

the four most sensitive organs and cells to radiation

• bone marrow

• intestines

• oral mucous membrane

• spermatogenic cells

what are the four cells of bone marrow?

• lymphoblasts

• lymphocytes

• plasma cells

• erythroblasts

what is the name of the relevant intestinal cells?

epithelial stem cells

what are the cells of the oral mucous membrane?

basal cells

what are the second most radio sensitive organs and cells?

skin and organs with epithelial linings

what is a specific epithelium that is the second most radio sensitive?

inner enamel epithelium

what is fairly sensitive organs and cells?

fine vasculature: bvs and endothelial cells

what are the second least radio sensitive organs and cells?

salivary glands, kidneys liver, pancreas

what is the least sensitive radio sensitive organs and cells?

muscles (striated muscle cells most mature), brain neurons (radio-resistant), spinal cord, erythrocytes

what are the two exceptions to the law of bergonie and tribondeau?

• small lymphocytes

• oocytes

although they are mature they are radio sensitive

what are the teratogenic effects of radiation on the embryo/fetus?

• intrauterine death - first week

• intra-uterine growth retardation - early wks

• congenital malformations - 8wks later

• developmental abnormalities - late

(the deterministic effects)

what are the stochastic effects of radiation on the embryo/fetus?

cancer in childhood

what are the two factors that influence probability of radiation effects on embryo?

• dose to embryo/fetus

• stage of gestation

what is the gestational age and radiogenic effects of the preimplantation stage?

• age: 0-9 days

• effects: all or none

what is the gestational age and radiogenic effects of the organogenesis stage?

• age: 10 days- 6wks

• effects: congenital anomalies, growth retardation

what is the gestational age and radiogenic effects of the foetal stage?

• age: 6 wks - 40 wks

• effects: growth retardation, microcephaly, mental retardation

what is the dose threshold that would produce x-ray induced birth defects?

100-250 mSv

wha is the dose of dental radiographs?

<0.1 mSv

prodromal symptoms:

• dose:

• time of onset:

• manifestation:

• dose: 1-2 Gy

• time of onset: min-hours

• manifestation: prodromal symptoms (specific)

hematopoietic symptoms:

• dose:

• time of onset:

• organs effected:

• pathophysiology:

• manifestation:

• death:

• dose: 2-7 Gy

• time of onset: days-mo

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

• pathophysiology order: lymphopenia/gran ulocytopenia, loss of platelets, erythrocyte depletion

• manifestation: hematopoetic symptoms ie infection, hemorrhage, anemia

• death: low or 10-30 days after irradiation if untreated

gastrointestinal syndrome:

• dose:

• time of onset:

• organs effected:

• pathophysiology:

• manifestation:

• death:

• dose: 7-15 Gy

• time of onset: wks-mo

• organs effected: small intestine

• pathophysiology: damage to intestinal villi, neutropenia

• manifestation: GI symptoms and circulatory collapse, hematopoietic too

• death: 3-10 days

central nervous system:

• dose:

• time of onset and death:

• organs effected

• pathophysiology

• manifestation

• dose: 50 Gy (~ atomic bomb)

• time of onset: death in 1-2 days

• organs effected: brain

• pathophysiology: damage to cerebra bvs leading to cerebral edema, damage to neurons

• manifestation: cardiovascular and CNS

what is the typical total dose of radiotherapy for oral cavity?

64-70 Gy in 6-7 wks; malignant oral lesions that are radiosensitive

what are the three areas that can be effected by radiation on oral tissues?

• mucous membrane

• taste buds

• teeth

• salivary glands

• bone

what are the 6 effects of radiation on mucous membranes?

• desquamation: shedding, peeling of skin as flakes

• inflam & pain

• white/yellow pseudomembrane

• secondary fungal infection

• long term: atrophic. thin, avascular mucosa

  • no oxy no nutrients =delayed healing

• healing 2 mo after

what are the two effects of radiation on taste buds?

• ↓ taste acuity

• recovery to almost normal 60-120 days post irradiation

what are the four effects of radiation on teeth? (think pre and post calci and erupted teeth)

• prior to calci: tooth bud destroyed

• post calci: malformations, arrested growth

• severity is dose dependent

• erupted teeth are radioresistant

what are the three effects of radiation on salivary glands?

• reduced secretion (xerostomia)

• pH altered decalci fo enamel

• radiation caries (bc salivary glands damaged)

what are the two effects of radiation on bone?

osteonecrosis:

• damage to vasculature pf periosteum, cortical one

• destruction of osteoblasts

what is the worst/most serious complication of radiation on the oral cavity?

osteoradionecrosis

could lead to jaw fracture