1. 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

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

3. 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.

4. Image of Normal Metaphase Spread

5. Dicentric Chromosome

6. 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

7. Multiple Dicentric Chromosomes

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

9. The Lymphocyte Micronucleus Test as a Radiation Biodosimeter

10. LyLLy

11. Lymphocyte in Normal Anaphase

12. Lymphocyte in Abnormal Anaphase

13. Micronucleus

14. X-Ray Therapy Machine

15. 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

16. Micronucleus Dose Response

18. The Micronucleus Test as a Biological Dosimeter
Linear Dose Response to X-rays
y = x
35.5 = x
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)

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

24. 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

25. 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

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

27. 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.

28. Questions