Chapter 5 - Effects of Long-Term Exposure to Radiation
Major Organogenesis
*2nd to 8th week after conception *radiation can cause CNS congenital anomalies at low LET
Fetal Growth stage
*9th week to term *negligible aberration at this stage *damage during this stage may not manifest until later in life, such as behavioral changes, reduced IQ, or cancer.
Breast Cancer
*Age dependent *Linear dose Response *Latent Period 10-40 yrs
Leukemia
*Can be ACUTE or CHRONIC *LYMPHOID or MYELOID *Judged to be Linear and Nonthreshold *Latent Period 4-7 yrs *at risk period 15-20 yrs *BEIR suggest Relative risk, nonlinear dose response relationship *Considerate a rare disease. *Most Frequent observed radiation induced cancer. *No evidence of radiation-induced leukemia in American Radiographers. *Radiation-Induced Leukemia decreases with age.
Skin Carcinoma
*Follows a Threshold dose response *latent period 5-10 yrs *Not present in current Radiology personnel
Osteosarcoma
*Radium Girls 1920's *Linear quadratic dose response relationship
Thyroid Cancer
*Responsible for Approx 12% of radiation induced cancer deaths *Benign or Malignant *Papillary or Follicular *Latent Period for Benign 5-35 yrs *Latent Period for Malignant 10-35 yrs *Linear, Nonthreshold dose response
Genetic Damage
*Studies in Fruit flies in 1927 by Herman Muller 1. no new or unique mutations are produced by radiation. 2. In doses range 25-400R the frequency of mutations was linear with dose 3. the majority of radiation-induced mutations were recessive 4. there were no dose rate or dose fractionation effects on going studies on Mullers research by Russell in 1946 1. radiation is a powerful mutagenic agent 2. the majority of mutations are unhealthy to the organism 3. there are no unique mutations produced by radiation 4. radiation induced genetic damage can occur as the result of a single mutation
Pre-Implantation Stage
*originates with the joining of sper and egg *continues to 9th day when zygote becomes deposited in uterine wall *fertilized egg is rapidly dividing *radiation can cause prenatal death or recovery.
Turner's Syndrome
Endocrine disorder caused by the failure of the ovaries to respond to pituitary hormone stimulation.
Parenchymal
Essential life sustaining cells
Absolute Risk Model
Estimates a continual increase in risk, independent of the age-specific cancer risk at time of exposure; also known as the additive risk model.
Carcinoma
Growth or Tumor
Radium
Half-life 1620 yrs
Limitations on epidemiologic studies include:
. Failure to control experimental group for know carcinogens . Insufficient observation . Using proper control group . Deficient/incorrect health records
Lung Cancer
.Linear nonthreshold
Sources of Data on incidence of radiation-induced cancer:
1. Atomic bomb survivors 2. Medically exposed patients 3. Occupationally Exposed personnel 4. Population that receive high natural background radiation
3 stages of Fetus
1. Pre-Implantation 2. Major Organogenesis 3. Fetal Growth Stage
Genetically Significant Dose (GSD)
An average calculated from the gonadal dose received by the entire population and used to determine the genetic influence of low dose to the whole population
Osteosarcoma
Bone Cancer
BEIR Committee
Committee on the Biological Effects of Ionizing Radiation
Non-stochastic
Deterministic; the severity of the injury increases with the dose, not the chance of it occurring
Ankylosing spondylitis
Immobility of the vertebrae
Myeloid
In Marrow
Lymphoid
In the lymph tissue
Absolute risk dose-response
Linear dose response
Life-Span Shortening and dose
Linear, non-threshold
Papillary
Nipple like protrusion
Benign
Nonprogressive
type of dose-reponse curve for Diagnostic and Occupational Exposures
Nonthreshold linear curve
Relative Risk Formula
Observed cases ------------------ Expected cases
BEIR Committee uses what risk model
Relative risk model
Life-Span Shortening
Studies on animals that received acute and chronic radiation indicated that animals that were chronically irradiated died younger than animals that were not irradiated.
Epidemiology
The Science that examines the incidence, distribution, and control of disease in population
Follicular
cavity
excess risk formula
observed cases - expected cases
Stochastic
occurring randomly in nature; the probability of being affected increases with the dose
progeny
offspring
Dose-Response Curve
predicts cancer risk in human population that have been exposed to low levels of radiation.
Malignant
progressive
radio-carcinogenesis
radiation producing cancer
Acute
rapid and severe
Chronic
slow and progressive
loci
spot, place of origin
Radiation Hormesis
the controversial hypothesis that chronic low doses of ionizing radiation stimulates repair mechanism that protect against disease.
doubling dose
the dose of radiation required per generation to double the spontaneous mutation rate.
Excess risk
the number of excess cases of cancer observed compared with expected spontaneous occurrence.
Neoplasms
tumor