Epidemiology :Epidemiology


Objectives :Objectives Discuss and describe epidemiology Discuss population used as sources Describe limitations on epidemiologic studies Describe different dose response curves Discuss Hiroshima-Nagasaki atomic bombings and radiation induced cancers Discuss and explain different risk models


Intro to Epidemiology :Intro to Epidemiology Epidemiology is the study of diseases in populations of humans or other animals, specifically how, when and where they occur. The science of epidemiology was first developed to discover and understand possible causes of contagious diseases such as: Small pox Thyroid polio


Epidemiology :Epidemiology Epidemiological studies can never prove causation cannot prove that a specific risk factor actually causes the disease being studied. evidence can only show that this risk factor is associated (correlated) with a higher incidence of disease in the population exposed to that risk factor. The higher the correlation the more certain the association, but it cannot prove the causation.


Epidemiology :Epidemiology First documented case of radiation-induced carcinoma (growth or tumor) In 1902, it was determined that radiation is carcinogenic (cancer causing) Incidence rates for radiation-induced cancer are determined by expected occurrence in a control group (general population) Occurrence in experimental group (the irradiated population)


Epidemiology :Epidemiology Population used as sources of data (cancer) Atomic bomb survivors Medically exposed patients Occupationally exposed personnel Populations who receive high natural background exposure


Epidemiology :Epidemiology Limitations on epidemiologic studies include: Failure to control experimental group for other known carcinogens Insufficient observation periods which permit full demonstration of cancers with long latent periods Using improper control groups Deficient or incorrect health records Studies can be divided into two basic types Whether the events have already happened(retrospective) (b) Whether events may happen in the future (prospective).


Dose Response Curves :Dose Response Curves Developed by scientist who predict cancer risk in human populations that have been exposed to low levels of ionizing radiation. Dose response curves are: Nonthreshold linear Linear quadratic Quadratic


Dose Response Relationships :Dose Response Relationships ”Since no radiation level higher than natural background can be regarded as absolutely 'safe,' the problem is to choose a practical level that, in the light of present knowledge, involves negligible risk.” -R.H. Clarke


Dose Response Relationships :Dose Response Relationships excess cancer malignancies among radiologists indications of excess leukemia cases in the survivors of the atomic bombings at Hiroshima and Nagasaki Epidemiological evidence Epidemiological evidence ”stochastic effects,” whose probability of occurrence, not the severity, was assumed to be proportional to the size of the dose.


Dose Response Relationships :Dose Response Relationships THE LINEAR DOSE-RESPONSE MODEL FOR RADIATION-INDUCED CANCER


Atomic Bomb Survivors :Atomic Bomb Survivors The principal scientific evidence that supports the LNT model is the 1950- 2020 Life Span Study of cancer mortality among the Hiroshima-Nagasaki survivors. The two A-bombs dropped in August 1945 killed between 150,000 and 200,000 of a total population of 429,000 people. The Life Span Study sample of 86,572 people contains roughly half of the survivors who were within 2.5 km of the bombs.


A-BOMB SURVIVORS' OBSERVED AND EXPECTEDDEATHS FROM SOLID CANCERS (1950-1990) :A-BOMB SURVIVORS' OBSERVED AND EXPECTEDDEATHS FROM SOLID CANCERS (1950-1990)


Relative Vs Absolute Risk :Relative Vs Absolute Risk The relative or multiplicative risk model Explains how age at the time of radiation exposure may influence the cancer risk estimate. The absolute or additive risk model Estimates continual increase in risk that is independent of the spontaneous age specific cancer risk at the time of exposure Excess risk Is another way to express risk. Expressed as number of excess cases observed compared with the expected spontaneous occurance.


Absolute Risk :Absolute Risk Absolute risk states risk in terms of number of cases 10⁶ persons/rad/year Risk assumes a linear dose-response relationship Excess risk Excess cases = observed cases – expected cases = ? The models most often used for expressing risk are the relative and absolute risk models.


Summary :Summary In conclusion we he discussed dose response curves and how it corresponds to the Hiroshima-Nagasaki bombing Understood concepts of Relative, Absolute and excessive risk models Learned the basics on epidemiology


References :References Shimizu Y, Kato H, Schull WJ. Studies of the mortality of A-bomb survivors. 9. Mortality, 1950-1985: Part 2. Cancer mortality based on the recently revised doses (DS86). Radiat Res 121:120-141 (1990). Gopal B Saha. (2006).Physics and Radiobiology of Nuclear Medicine- Third Edition. Cleveland, OH.; Springer Science+Buisness Media, Inc. Epidemiology. (2008). In Wikipedia. Retrieved June 9, 2008, from Wikipedia Online: http://en.wikipedia.org/wiki/Epidemiology


Question 1 :Question 1 What is the definition of epidemiology?


Answer 1 :Answer 1 Epidemiology is the study of diseases in populations of humans or other animals, specifically how, when and where they occur.


Question 2 :Question 2 The science of epidemiology was first developed to discover what type of contagious diseases?


Answer 2 :Answer 2 Small pox Thyroid polio


Question 3 :Question 3 T/F Epidemiology studies can always prove causation?


Answer 3 :Answer 3 FALSE! Epidemiological studies can never prove causation


Question 4 :Question 4 Occurrence in experimental group (the irradiated population) Expected occurrence in a control group uses what type of population in the study?


Answer 4 :Answer 4 expected occurrence in a control group (general population)


Question 5 :Question 5 Studies can be divided into two basic types. What are their names?


Answer 5 :Answer 5 Studies can be divided into two basic types retrospective prospective


Question 6 :Question 6 What are the three dose response curves?


Answer 6 :Answer 6 Nonthreshold linear Linear quadratic quadratic


Question 7 :Question 7 What are the three risk models and explain each


Answer 7 :Answer 7 The relative or multiplicative risk model Explains how age at the time of radiation exposure may influence the cancer risk estimate. The absolute or additive risk model Estimates continual increase in risk that is independent of the spontaneous age specific cancer risk at the time of exposure Excess risk Is another way to express risk. Expressed as number of excess cases observed compared with the expected spontaneous occurance.


Question 8 :Question 8 What is the absolute risk in terms of numbers?


Answer 8 :Answer 8 10⁶/rads/year


Question 9 :Question 9 Name population sources used for data on epidemiology


Answer 9 :Answer 9 Atomic bomb survivors Medically exposed patients Occupationally exposed personnel Populations who receive high natural background exposure


Question 10 :Question 10 What year was the first documented radiation induced carcinoma? 1916 1902 1910


Answer 10 :Answer 10 (B) 1902