EPIDEMOLOGY and RISK ESTIMATION MODELS :EPIDEMOLOGY and RISK ESTIMATION MODELS GIPSY MORALES


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


EPIDEMIOLOGY :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 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) 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 THE LINEAR DOSE-RESPONSE MODEL FOR RADIATION-INDUCED CANCER


ATOMIC BOMB SURVIVORS :ATOMIC BOMB SURVIVORS The two A-bombs dropped in August 1945 killed between 150,000 and 200,000 of a total population. Around 93,000 were exposure at the time of the bombing. Approximately 20,000 received doses between 1-5 cGy while ~1,1000 received doses in excess of 2 Gy


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


Risk model :Risk model 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 occurrence


Risk model :Risk model Absolute risk states risk in terms of number of cases 10⁶ persons/rad/year Excess risk Observed cases–expected cases Relative risk Observed cases/ expected cases


SUMMARY :SUMMARY Epidemiology is the study of diseases in populations of humans or other animals The science of epidemiology was first developed to discover and understand possible causes of contagious diseases such as: small pox, Thyroid, polio Epidemiological studies can never prove causation In 1902, it was determined that radiation is carcinogenic (cancer causing) expected occurrence in a control group (general population) Population used as sources of data (cancer) Atomic bomb survivors Medically exposed patients Occupationally exposed personnel Studies can be divided into two basic types: retrospective and prospective


SUMMARY :SUMMARY Dose response curves are: Nonthreshold linear, linear quadratic, quadratic The three risk models are: The relative, the absolute and the excess risk Absolute risk states risk in terms of number of cases is: 10⁶ persons/rad/year


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 :QUESTION What is the definition of epidemiology? Epidemiology is the study of diseases in populations of humans or other animals 2. T or F: The science of epidemiology was first developed to discover and understand possible causes of contagious diseases T or F: Epidemiology studies can always prove causation? FALSE!, Epidemiological studies can never prove causation


QUESTION :QUESTION 4. What are the three dose response curves? Nonthreshold linear, Linear quadratic, quadratic What is the absolute risk in terms of numbers? 10⁶/rads/year Name population sources used for data on epidemiology Atomic bomb survivors, Medically exposed patients, Occupationally exposed personnel, Populations who receive high natural background exposure


QUESTION :QUESTION Expected occurrence in a control group uses the irradiated population in the study? T or F FALSE Studies can be divided into two basic types. What are their names? retrospective and prospective 9. What year was the first documented radiation induced carcinoma? a)1916 b) 1902 c) 1910 10. What are the three risk models relative, absolute, and excess risk