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RADIATION EPIDEMIOLOGY AND LEUKEMIA B.Ledoshchuk, M . D.,Ph . D.

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### RADIATIONEPIDEMIOLOGYAND LEUKEMIAB.Ledoshchuk, M.D.,Ph.D.

### Reliability of the Diagnoses

Institute of Epidemiology

Research Center for Radiation Medicine of Ukraine

Kyiv-2001

EPIDEMIOLOGY OF LEUKAEMIA

Results of the 10-year study of leukemia among the Chernobyl accident clean-up workers in Ukraine

1986-96

- EPIDEMIOLOGY
- studies the occurrence and prevalence of diseases among population
- identifies disease cases
- determines probable relationship between various risk factors

UNIVERSITIES AND INSTITUTES OF EPIDEMIOLOGY

ENGLAND

14

CANADA

13

WESTERN

EUROPE

26

USA

89

UKRAINE

1

AUSTRALIA

12

AFRICA-ASIA

5

Types of Epidemiology

- medical
- pharmaceutical
- veterinary
- environmental
- insurance

Classification of medical epidemiology

- Infection epidemiology
- Generalepidemiology
- Environment epidemiology
- Clinical epidemiology
- Military epidemiology
- Epidemiology of insurance

Methods of analytical epidemiology

Cohort study, Follow-up study

Investigation for a certain period of time of a group of people defined prior to onset of disease

- Registration of new disease cases
- Exposed group (clean-up workers-86 )
- Unexposed group(clean-up workers-87, 88-90 )
There is a risk of healthy worker effect in comparison with population (underestimation IR in exposed group)

Methods of analytical epidemiology

Case/control studies

- Investigation of groups of people defined by presence or absence of disease
- Case - ( patient) exposed and unexposed
- Control - (healthy) exposed and unexposed
- Only estimation of relative risk is possible
RR (relative risk) or OR (odds ratio)

EPIDEMIOLOGYOF LEUKAEMIA

- Goal of research:
Define the dependenceof incidence of leukemia among Chernobyl accident clean-up workers (ACW) on the year of participation in emergency works and period of time that passed since exposure to radiation

EPIDEMIOLOGYOF LEUKAEMIA

Results and discussion

- Subject of observation:
Chernobyl accident clean-up workers (ACW), males, included in State Chernobyl Registry of Ukraine.

- The number of persons under study at the end of the observation period
is 179 026 .

EPIDEMIOLOGYOF LEUKAEMIA

Sources of information

- State Registry of victims of Chernobyl accident (CA)
- specialized registries and subregistries
- primary data from medical clinics
- data of official disease registration and death cases registration
- special selective registration of cases
- data of expert commission for victims of CA

EPIDEMIOLOGYOF LEUKAEMIA

Main sources of information for case search:

- Results of annual medical examination of ACW
- Regional hematological clinics data

EPIDEMIOLOGYOF LEUKAEMIA

Main methods of obtaining of information :

- retrospective
- current
- passive
- active

EPIDEMIOLOGYOF LEUKAEMIA

Period of observation ACW:

1987-1996

Calculation were performed for 5-year intervals

1987-1991, 1992-1996

EPIDEMIOLOGYOF LEUKAEMIA

Diagnostic criteria

- - under-record of cases due to strong diagnostic criteria
- - over-record of cases (including irrelevant to the diagnosis cases) due to insufficient demands to diagnosis

Classification of diseases

Choice:

- Etiology
- patogeneses
- Localizations disease
- ICD-9 orICD-10
- Clinical (FAB) Classification of Leukaemia

Reliability of the Diagnoses

the Factors influencing the quality

of the diagnoses

- subjective, objective symptoms; outcomes of laboratory and tool researches
- Diagnostic criterions (the majority of diseases has no precise criterions)
- Classification of diseases (in case of indeterminacies; vague, not updated cases)
- Reliability of the diagnosis - autopsy (types of researches)
- interpretation errors of classification

- Strict selection of cases
- Loss of true diseases

- Soft selection of cases
- Deriving cases not have significance

Gipo

diagnostics

Giper diagnostics

Sensitivity and specificity

Under the sensitivity one understand probability that,

the patient canl be classified as the patient

Numberof the patients classified as the patients

Se = Total number of the patients

Under the specificity one understand to probability that healthy can be classified as healthy

Number of Healthy, classified as healthy

Sp = Total number of healthy

MODEL of SENSITIVITY And SPECIFICITYA. Ahlbom, S.Norel 1990

Classified

cs the patients

The patients

The population

Healthy

classified

as the patients

The patients

classified

as healthy

(Is false

Negative)

(Is false

Positive)

The patients classified

as the patients

Information flows between institutions and the center

- cCITY HOSPITAL
- DDISPENSARY
- OBLAST HOSPITAL OBLAST DISPENSARY
- INSTITUTIONAL HEMATOLOGICAL DEPARTMENTS

CENTER FOR RADIATION MEDICINE

EPIDEMIOLOGYOF LEUKAEMIA

LEUKEMIA DIAGNOSIS STRUCTURE

There are 48 cases of leukemia

among clean-up workers of 1986

- 13 – acute leukemia - AL (27 %),
- 20 – CLL (42 %),
- 14 – CML (29 %),
- 1 – other forms of leukemia (2 %).

EPIDEMIOLOGYOF LEUKAEMIA

LEUKEMIA DIAGNOSIS STRUCTURE

There are 15 cases of leukemia

among clean-up workers of 1987

- 8 cases of AL (53 %),
- 2 cases of CLL (13 %),
- 4 cases of CML (27 %),
- 1 case of unspecified leukemia (7 %).

EPIDEMIOLOGYOF LEUKAEMIA

LEUKEMIA DIAGNOSIS STRUCTURE

There are 8 cases of leukemia

among clean-up workers of 1988-90

- 1 case of AL ,
- 4 cases of CLL,
- 3 cases of CML.

EPIDEMIOLOGYOF LEUKAEMIA

LEUKEMIA DIAGNOSIS STRUCTURE

GENERAL EPIDEMIOLOGY

- Crude measure – calculated for population as a whole
- Specific measure – calculated for specific groups of population
- Standardized measure – for completion of summary comparison between two or more groups diversified according to age or other criteria

GENERAL EPIDEMIOLOGY

Generate rate

- Absolute rate (number)
- Popularity
- Morbidity
- Mortality
- Expressed as cases from 106 to 103 in investigated cohort (case/control)

GENERAL EPIDEMIOLOGY

Popularity

prevalence rate, ratio - PR

- It is a quota of morbidity among population in certain moment of time
PR =number of existing cases of disease

population during the same of time period

GENERAL EPIDEMIOLOGY

Morbidity

incidence rate - IR

Represents rate at which new cases are occurring.

- IR =number of new cases of disease over a specified time period
person-years, person-time, time at risk

GENERAL EPIDEMIOLOGY

CUMULATIVE INCIDENCE

- cumulative incidence rate - CI
- It is a quota of healthy persons that can fall ill during a certain period of time
- CI =number of new cases over a specified time period
population at the beginning of a specified time period

- , where IR – incidence rate – duration of observation period

GENERAL EPIDEMIOLOGY

confidence interval

Calculation of 95% confidence intervals for

- prevalence rate (PR)
- cumulative incidence rate (CI)
- incidence rate (IR)
IR1.96 (R- person-years)

confidence interval

Calculation of 95% confidence intervals for

- relative risk
where e - logarithmic base = 2,718

ln - logarithmic function with e base (natural logarithm)

ln(RR) - survey number

= square root of dispersion var calculated number

GENERAL EPIDEMIOLOGY

Calculation of Relative Risk

For cumulative incidence RR=(A1/N1)/(A0/N0)

where А=number of cases

N=number of person year

95% confidence interval for relative risk ln(RR)-dispersion

var[ln(RR)] =[(N1-A1)/(N1*A1)]+[(N0-A0)/(N0*A0]

GENERAL EPIDEMIOLOGY

Calculation of Relative Risk

For incidence rate RR=(A1/R1)/(A0/R0)

where А=number of cases

R=number of person-years

95% confidence interval for relative risk

ln(RR)-dispersion

var[ln(RR)] =(1/A1)+(1/A0)

GENERAL EPIDEMIOLOGY

Stratification

- Division of the population into subgroups (strata) if there is the base to assume that the incidence is unequal in different groups
- strata distribute according to:
- age
- sex
- occupation
- radiation dose
- other effects

GENERAL EPIDEMIOLOGY

Standardization

- is one of the method of comparison validity

- direct method of standardization
- indirect method of standardization

GENERAL EPIDEMIOLOGY

Direct Method of Standardization

- within group, intergroup and international standard age is used for comparison of incidence rates in two groups
- ratio of standardized incidence rates is presented by formula
(R1.1/R1.n)*RR1.1+(R1.2/R1.n)*RR1.2=ASR1

(R2.1/R2.n)*RR2.1+(R2.2/R2.n)*RR2.2=ASR2

GENERAL EPIDEMIOLOGY

indirect method of standardization

SIR(O/E)*100(standardized incidence ratio SIR)

- ratio of O-observed number of cases at exposed group and E - expected number of cases at control group
- standard age of exposed group is used for comparison incidence rates in two groups

E= (N1*IR1)+(N2*IR2)

EPIDEMIOLOGYOF LEUKAEMIA

EPIDEMIOLOGYOF LEUKAEMIA

EPIDEMIOLOGYOF LEUKAEMIA

EPIDEMIOLOGYOF LEUKAEMIA

Age Standardized Rate (per 100.000)

-Number of cases from 20 to 29 years/1000,000

clean-up workers of 1986 - А1 1987г. – B1

-Number of males from 20 to 29 years/100,000

clean-up workers of 1986 - A2 1987г. – B2

Calculation

For clean-up workers of 1986 A1*(12,000/A2)=ASR1

For clean-up workers of 1987 B1*(12,000/B2)=ASR2

where 12,000 – world standard in this interval

EPIDEMIOLOGYOF LEUKAEMIA

EPIDEMIOLOGYOF LEUKAEMIA

Design formulasof relation between exposure and incidence

- COHORT

data are presented as relation risk estimation

RR=IR1 / IR0

where IR1 and IR0 are incidence coefficients

A1 and A0 - number of cases

R1 и R0 - person-years at risk

Design formulasof relation between exposure and incidence

- CASE-CONTROL

relative risk estimation -

odds ratio (OR)

where A1=a, A0=b

R1=c, R0=d

A1 andA0 - number of cases

R1 andR0 - person-years at risk

From NCRP Report No: 93

PENENTRATING RADIATION

Alpha Particles

Radiation Source

Stopped by a sheet of paper

Beta Particles

Stopped by a layer of clothing or by a few millimeters of a substance

Stopped by several feet of concrete organic tissue or a few inches of lead

Gamma Rays

RADIO-BIOLOGICAL EFFECTS

NOT STOCHASTIC EFFECTS

- as a result of high irradiation acute radiation sickness and furnaces radiation injuries are developed
STOCHASTIC EFFECTS

- developed during prolonged irradiation (external, internal, balanced, critical organs etc.) Somatic, genetic, embryo toxic

RADIO-BIOLOGICAL EFFECTS

STOCHASTIC EFFECTS

- Somatic and genetic, embryo toxic effects are developed in casual, probabilistic nature
- Only probability of damage appearance depends on dose, but not weight and depth of damage
- Frequency of appearance radiation-induced diseases increases with dose increase

RADIO-BIOLOGICAL EFFECTS

STOCHASTIC EFFECTS

- Summary stochastic effects during population irradiation (population group) are defined by collective dose
- It is impossible to define an individual effect or additional risk and it is impossible to determine which kind of cancer is typical for additional cases

MODELS of EXCESSof RISKSD.Pierce, D.Preston, 1996-1999

Time dependent models of redundant relative risk for solid swellings

Limit of models of risk for a cancer = 10 years

Absolute risk for leukaemia

Limit of models leukaemia = 2 years

The limit of models of risk is a concept latent

Period - between the beginning of effect of the radiation factor and diagnostics leukaemia

MODELS of EXCESSof RISKSD.Pierce, D.Preston, 1996-1999

Execes absolute risk for leukaemia

Where and - constant: - depends on categories -

Age for want of effect and, for each from these categories, categories of time from time of effect and sex

D – Doze equivalent red marrow, inSiverts(Sv)

MODELS of EXCESSof RISKSD.Pierce, D.Preston, 1996-1999

- Time dependent models of redundant
relative risk adapt DOSE dependence

As linear for SOLIDCANCERS

As linearly – quadratic for LEUKAEMIA

EPIDEMIOLOGYOF LEUKAEMIA

RESUME:

- The comparative analysis was done for clean-up workers CWA of 1986 and 1987 by periods of observation of 1987-1991 and 1992-1996.
- The results of the conducted study indicate the increasing of the leukemia risk among CWA of 1986 most vividly during 1987-1991.
- Relative risk was defined at the level of 3,32 (1,08; 10,20), and for 20-59 age group it was 3,45 (1,15; 10,36).

- No significant differences were defined in leukemia incidence at survey groups in 1992-1996.

Ledoshchuk Boris Alexandrovich born in 1946 in Russia. In 1970 graduated from Blagoveschensk Medical Institute, where also studied in coordinator and at post-graduate course. In 1975 – 1978 worked in the Institute of clinical and experimental medicine of the Academy of Sciences of USSR in Novosibirsk. Took part in scientific epidemiological studies of Far-East and Siberia regions inhabitants. In 1978 – 1985 possessed various positions in medical institutions of Nikolaev region (Ukraine).

In 1986 – 1988 worked in the Ministry for Health Care of Ukraine where was responsible for rehabilitation programmer of the population of Chernobyl contaminated area.

Since 1988 heads scientific leukemia epidemiology laboratory of the Radiation Medicine Scientific Center. In 1995 – 2000 headed the Medical Department of the Ministry of Atomic Energy.

Since 27 April 1986 was involved in clean-up works in the Chernobyl area.

One of the leading specialists in the problems of automatic systems of long-term medical monitoring of people damaged in result of Chernobyl accident (State Registry of Ukraine).

Author of more than 100 scientific articles and works on the problems of epidemiology, automatic systems of registration and radiation medicine. Prominent participant of international epidemiology projects: AIFIKA, Chernobyl, Leukemia.

B. A. Ledoshchuk

M.D.,Ph.D.

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