Biological Dosimetry in Radiation Accidents Andrzej Wojcik Department of Radiobiology and Health Protection Institute for Nuclear Chemistry and Technology Warszawa Department of Radiobiology and Immunology Insitute of Biology Swietokrzyska Academy Kielce

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 measurement with a calibration curve that is generated under in vitro conditions

The material of choice for biological dosimetry is 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 G 0

The principle of blood lymphocyte culture culture time = 48h Phytohaemaglutinine Colcemid harvest slide praparation staining culture time = 72h Cytochalasin B Analysis of chromosomal aberrations Analysis 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 reciprocal translocation

The frequency of radiation-induced aberrations is the same in lymphocytes exposed under in vivo and in vitro conditions 0 – 3 Gy Dose (Gy) Frequency Y A calibration curve

Dicentric Translocation Is it better to analyse unstable aberrations like dicentrics 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 exposure K. Buckton et al., 1983 Years after exposure Percent cells with translocations cells with dicentrics Aberrations in Lymphocytes of patients with Morbus Bechterew who were treated with radiotherapy t 1/2 = 3 years Frequency of dicentrics remains stable for several weeks that of translocations – for several years

Distribution of radiation-induced dicentrics Whole body exposure Partial body exposure Poisson distribution Number of aberrations Number of cells Example of a distribution var m = 1 (dispersion index, relative variance) Overdispersed distribution var m > 1 m = 0,34 ab/cell How to detect partial-body exposure The degree of deviation from a Poisson distribution allows to 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 mid Autumn 1997: 7 soldiers were treated in Ulm, Germany 4 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 + bD 2 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)bD 2, where x = t/t 0 with t being the time over which the radiation occurred and t 0 the mean lifetime of breaks PatientAcute dose (Gy) Dolphin (Gy) Percent of lymphocytes irradiated Qdr (Gy) Function G (Gy) AN 1.2   0.8 EP 1.6   1.0 CG 0.7   0.5 TK 0.5   0.4 EPR    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 lymphocytes solution: Premature Chromosome Condensation - PCC culture time = 48h Phytohaemaglutinine okadaic acid calyculin A harvest slide praparation staining G 2 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 Caclulated doses Doses confirmed by measurement of 24 Na ( 22 Na → 24 Na)

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 Center 27th February patients treated for mamma Ca (post-operative RT) were exposed to a single dose of 8 MeV electrons patient number number of fractions received before accident Dose measured by the physicist immediately after the accident: 103 Gy Validity of measurement questioned by the manufacturer of the accelerator

Dose effect curves for aberrations and micronuclei in lymphocytes irradiated in vivo (radiotherapy patients) and in vitro Venkatachalam et al. Mutat. Res 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 E in E ex absorbed energy (J) mass (kg) Equivalent whole body dose (EBWD) E in E ex 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 Frequency of aberrations dose-response curve of proper radiotherapy dose-response curve of accident patients Accident dose The idea behind the strategy of comparing the aberration frequencies found in lymphocytes of accident patients with the dose-response curve plotted on the basis of data from properly treated breast cancer patients

Dose-response curves for accident patients and for control (properly treated) breast cancer patients Wojcik et al. Radiation Research 160: , 2004

Bone = hydroxyapatite crystals Ca 10 (PO 4 ) 6 (OH) 2 bound by collagen The paramagnetic centres occur in carbonated apatites = hydroxyapatite crystals where some of the OH - or PO 4 3- have been replaced by carbonate ions CO 3 2- Bone tissue can contain up to 8% of these. Tooth enamel - more. The principle of Electron Paramagnetic Resonance EPR CO 2 - t ½ = a

EPR: Electron Paramagnetic Resonance example of an extrapolation curve

Dose estimation by EPR Patient 3Patient 4Patient 5 frontal position 59  7 64   3 distal position 67  8 84   5 calculation based on physical 103  9 83   9 measurement Accident doses received by Patients 3, 4 and 5 estimated at a tissue depth of 1.9 cm (d max of 8 MeV electrons). The bottom line values were derived from the physical measurement perfomed by the local medical phisics team immediatelly after the accident.

Patient 4 EPR analysis Gy Patient 3 EPR analysis Gy Patient 2 ? ? Patient 1 ? Patient 5 EPR analysis Gy Bialystok accident: frequencies of chromosomal aberrations and doses estimated by EPR Wojcik et al. Radiation Research 160: , 2004