Biological Dosimetry in Radiation Accidents

Andrzej Wojcik

Department of Radiobiology and Health ProtectionInstitute for Nuclear Chemistry and Technology

Warszawa

Department of Radiobiology and ImmunologyInsitute of Biology

Swietokrzyska AcademyKielce

Why is it important to perform biological dosimetry in case of a radiation accident?

Phases of the Acute Radiation Syndrome

P. Gourmelon et al. 2004

The principle of biological dosimetry

Biological dosimetry is a method of dose assessment on the basis of radiation-induced damage in the body

The methods

• Electron paramagnetic resonance (EPR) Application: teeth, bones – partial body exposure

• Chromosomal Aberrations and Micronuclei in peripheral blood lymphocytes. Application: whole- and partial-body exposure

Both methods rely on comparing the results of a measurementwith a calibration curve that is generated under in vitro conditions

The material of choice for biological dosimetryis the human peripheral blood lymphocyte

Lymphocytes circulate around the body, so some of them are always exposed even in cases of partial-body exposure

Lymphocytes can be collected easily

Lymphocytes are to over 95% in the resting phase G0

The principle of blood lymphocyte culture

culture time = 48h

Phytohaemaglutinine

Colcemid

harvestslide praparationstaining

culture time = 72hCytochalasin B

Analysis of chromosomal aberrationsAnalysis of micronuclei

?

dic

ace

A mitotic cell with chromosomal aberrations

Analysis of chromosomal aberrations by fluorescence in situ hybridization (FISH)

chromosome 2

chromosome 8

chromosome 14

reciprocaltranslocation

The frequency of radiation-induced aberrationsis the same in lymphocytes exposed under

in vivo and in vitro conditions

0 – 3 Gy0 – 3 Gy

Dose (Gy)

Fre

qu

ency

Y

A calibration curve

Dicentric

Translocation

Is it better to analyse unstable aberrations likedicentrics or stable aberrations like translocations?

restitution

Dicentric Translocation

initial damage

Micronucleus

How stable with time are dicentrics and translocations?

Frequencies of aberrations as function of time post exposureK. Buckton et al., 1983

Years after exposure

Per

cen

t

cells with translocationscells with dicentrics

Aberrations in Lymphocytes of patients with Morbus Bechterewwho were treated with radiotherapy

t1/2 = 3 years

Frequency of dicentrics remains stable for several weeksthat of translocations – for several years

Distribution of radiation-induced dicentrics

Whole bodyexposure

Partial bodyexposure

Poisson distribution

Number ofaberrations

Numberof cells

012345

7024

5000

Example of a distribution

varm = 1 (dispersion index, relative variance)

Overdispersed distribution

varm > 1

m = 0,34 ab/cell

How to detect partial-body exposure

The degree of deviation from a Poisson distribution allowsto assess the size of the exposed part of the body

11 young frontier guards were exposed to one or several sources of Cs-137 not exceeding 150 GBq at the Lilo military training center 20 km to the east of Tbilisi, from mid 1996 - mid 1997.

Autumn 1997:7 soldiers were treated in Ulm, Germany4 soldiers were treated inParis, France

Problem 1: partial body exposure, Problem 2: chronic exposure

ad 1. Dolphin or Qdr methods: allow the reconstruction of dose received by blood which was exposed and the part of the body which was exposed.

ad 2. G-function: Dose response relationship: Y = aD + bD2

A coefficient G is added to the parameter b, reducing it to 0, when the DNA repair time exceeds the irradiation time (> 6 hours). The dose-effect curve becomes Y = aD + (Gx)bD2 , where x = t/t0

with t being the time over which the radiation occurred and t0 the mean lifetime of breaks

Patient Acute dose (Gy)

Dolphin (Gy)

Percent oflymphocytes

irradiated

Qdr (Gy)

Function G (Gy)

AN 1.2 0.2 2.3 0.40 2.8 3.1 0.8

EP 1.6 0.3 2.5 0.50 3.4 4.3 1.0

CG 0.7 0.2 - - - 1.0 0.5

TK 0.5 0.2 - - - 0.7 0.4

EPR

-

4.5 0.3

1.4 0.4

1.5 0.2

The Tokaimura criticality accident

September 30, 1999, uranium conversion test plant of JCO Co. Ltd. in Tokai-mura, 115 km northeast from the center of Tokyo. Three workers (A, B and C) were involved in the process of enriching U-235.The criticality chain reaction started when B was pouring uranyl nitrate solution into a tank through a peephole, while A who was standing beside the tank supported the funnel that was inserted into that hole. C, the supervisor, was in the next room.

The problem: extremely high dose, causing mitotic delay of lymphocytessolution: Premature Chromosome Condensation - PCC

culture time = 48h

Phytohaemaglutinineokadaic acidcalyculin A harvest

slide praparationstaining

G2 PCC

S PCC

Worker A died after 81 days, worker B after 210 days. Patient C is alive.

Frequencies of PCC-aberrations in lymphocytes of Tokaimura victims

Ab

erra

tio

ns

per

cel

l

0

2

4

6

8

10

12

14

worker A worker B worker C

24.5 GyEq(16 - 30)

8.3 GyEq(6.9 - 10)

3.0 GyEq(2.8 - 3.2)

Caclulated doses

Doses confirmed by measurement of 24Na (22Na → 24Na)

Biological dosimetry in accidents during radiotherapy Problem:• Extreme partial-body exposure• Effect of fractionated doses before accidental exposure

In none of the accidents that occurred since the 70-ties until the Bialystok accident was it necessary to apply biological dosimetry for dose reconstruction

The radiological accident at the Białystok Oncology Center27th February 2001

5 patients treated for mamma Ca(post-operative RT)were exposed toa single dose of 8 MeV electrons

patient numbernumber of fractions

received before accident

1 1 2 24 3 10 4 21 5 2

Dose measured by the physicist immediately after the accident: 103 GyValidity of measurement questioned by the manufacturer of the accelerator

Dose (Gy)

0 1 2 3 4 5 6 7 8

Fre

quen

cy p

er 1

00 c

ells

0

20

40

60

80

100

in vitro dicentrics - dashed line

in vitro micronuclei - solid line

in vivo dicentrics - dashed line

in vivo micronuclei - solid line

Dose effect curves for aberrations and micronuclei in lymphocytes irradiated in vivo (radiotherapy patients) and in vitro

Venkatachalam et al. Mutat. Res. 1999

Problem 1: no appropriate calibration curve available

Solution:Analysis of aberrations in lymphocytes of breast cancer patients undergoing a correct radiotherapy

Absorbed dose =

1 Gy = 1 Joul / kg

Ein Eexabsorbed energy (J)mass (kg)

Equivalent whole body dose (EBWD)

Ein Eex

EWBD =absorbed energy (J)

body mass (kg)

1 Gy EWBD = Σ J / body mass

Problem 2: how to bring the doses absorbed during therapy to a common denominator

Absorbed Dose vs Equivalent Whole Body Dose

EWBD

Fre

qu

ency

of

aber

rati

on

s

dose-response curve of proper radiotherapydose-response curve of accident patients

Accident dose

The idea behind the strategy of comparing the aberration frequenciesfound in lymphocytes of accident patients with the dose-response

curve plotted on the basis of data from properly treatedbreast cancer patients

EWBD (Gy)

0 1 2 3 4 5

Dic

entr

ics

per

100

ce

lls

0

10

20

30

40

50

A1 A5

A3

A4

A2

Accident patientsControl patients

C7

Dose-response curves for accident patients andfor control (properly treated) breast cancer patients

Wojcik et al. Radiation Research 160: 677-683, 2004

Bone = hydroxyapatite crystals Ca10(PO4)6(OH)2 bound by collagen

The paramagnetic centres occur in carbonated apatites= hydroxyapatite crystals where some of the OH- or PO4

3- have been replaced by carbonate ions CO3

2-

Bone tissue can contain up to 8% of these. Tooth enamel - more.

The principle of Electron Paramagnetic Resonance EPR

CO2-

t ½ = 160 000a

EPR: Electron Paramagnetic Resonance

example of an extrapolation curve

Dose estimation by EPR

Patient 3 Patient 4 Patient 5

frontal position 59 7 64 11 71 3distal position 67 8 84 19 78 5

calculation basedon physical 103 9 83 9 103 9measurement

Accident doses received by Patients 3, 4 and 5 estimated at a tissue depth of 1.9 cm (dmax of 8 MeV electrons). The bottom line values were derived from the physical measurement perfomed by the local medical phisics team immediatellyafter the accident.

EWBD (Gy)

0 1 2 3 4 5

Dic

entr

ics

per

10

0 ce

lls

0

10

20

30

40

50

A1 A5

A3

A4

A2

Accident patientsControl patients

C7

Patient 4EPR analysis53 - 103 Gy

Patient 3EPR analysis52 - 76 Gy Patient 2

?

?Patient 1

?

Patient 5EPR analysis68 - 83 Gy

Bialystok accident: frequencies of chromosomalaberrations and doses estimated by EPR

Wojcik et al. Radiation Research 160: 677-683, 2004