Sensitivity of Human Lymphocytes to Low-Dose Radiation Gordon K. Livingston, PhD Technical Director, Cytogenetic Biodosimetry Laboratory Radiation Emergency Assistance Center Training Site Oak Ridge Insitute for Science and Education Oak Ridge, TN 37831 Gordon.Livingston@orise.orau.gov http://orise.orau.gov/reacts

Cytogenetic Biodosimetry Cytogenetic analysis provides a method to estimate radiation dose to individuals exposed to ionizing radiation when physical dosimetry devices are not available.

Lymphocytes Lymphocytes serve as ideal biological dosimeters because they: are very sensitive to radiation, are readily available in routine blood samples, circulate throughout the body, can be easily cultured and induced to divide in vitro respond consistently to ionizing radiation exposure by expressing chromosomal DNA damage in a dose-dependent manner.

Image of Normal Metaphase Spread

Dicentric Chromosome

Dicentric Chromosome Assay Low background rate (1-2 per 1,000 cells) Independent of age and gender Sensitivity range (0.2 – 5 Gy) Specificity to radiation is high Consistent radiation dose-response Proven in accidents over four decades Considered the gold standard

Multiple Dicentric Chromosomes

Typical Dose Response Curves Y=aD+bD2 Quadratic (linear-quadratic) Y=aD Linear Dicentrics/cell Dose [Gy]

The Lymphocyte Micronucleus Test as a Radiation Biodosimeter

LyLLy

Lymphocyte in Normal Anaphase

Lymphocyte in Abnormal Anaphase

Micronucleus

X-Ray Therapy Machine

X-ray Exposure Conditions Westinghouse Orthovoltage Therapy Unit 78 kV, 5 mA, 2mm Al added filtration output measured at 19.8 cGy/min at 50 cm 30 cm field size with +/- 10 % uniformity graded doses of 0, 5, 10, 15, 20 & 25 cGy 10 ml media (3-4 x 105 cells/ml) in 25 cm2 culture flasks at 37 C for 72 hr

Micronucleus Dose Response

The Micronucleus Test as a Biological Dosimeter Linear Dose Response to X-rays y = 2.783 x + 3.714 35.5 = 2.783 x + 3.714 X = 11.4 c Gy NCRP Dose to red marrow is 0.2 m rad / micro Ci 48,000 micro Ci x 0.2 m rad = 9,600 m rad = 9.6 rad (9.6 c Gy)

Red 1, 2 & 4 Green 3, 5 & 6

Cytogenetic Biodosimetry Limitations Large event could overwhelm resources Labor intensive Samples require shipment Advantages Proven method for dose estimation Amenable to web-based image scoring Existing resource of clinical laboratories

Cytogenetic Dosimetry Capacity Worldwide Cytogenetic labs and regional networks already collaborating with WHO: North-American Latin American (with IAEA support) European Scandinavian Eastern Europe: RF and Ukraine Western-Pacific: Japan, S. Korea, Australia Need to integrate and coordinate these networks globally Need a clear concept of operations for emergencies and in "quiet" time to make the most of these labs joint capabilities

Consortium Lab in Consortium (Metafer System) REAC/TS CBL Secure Central Server (Access Limited) Lab in Consortium (Metafer Software) Satellite Scoring Station (Metafer Software)

The re-establishment of the REAC/TS-Cytogenetic Biodosimetry Laboratory, operated by the Oak Ridge Institute for Science and Education (ORISE), was supported by: DOE-NNSA, DOE-EH, and Nuclear Regulatory Commission. Establishing a Web-Based International Radiation Cytogenetic Biodosimetry Consortium at REAC/TS is being funded by DOE-NNSA.

Questions