A Generalized Biodosimetry System for Human Radiation Exposure
In human radiation exposure, the dose distribution is usually non-uniform, due to dose attenuation (externalexposure), non-random hit by decay of radionuclide (internal exposure), or dilution of the exposed cells by tissue
recovery (past exposure). The method has been developed to estimate the dose components in non-uniform
distribution of radiation dose by unfolding chromosome aberration distribution into a dose distribution profile (M.
S. Sasaki, Int. J. Radiat. Biol., 79:83-97, 2003).
The rationale of the method is that the observed frequencies of cells with r aberrations is a mixture ofsubpopulations each having a specific mean frequency, mi, which is defined by specific dose, Di.
i =034

External
exposure

Past
exposureiCell density

12Internal
exposure

The overall aberration frequency, f(r), of cells with r aberrations should follow a mixed Poisson distribution asexpressed bynr
2f (r ) = ∑ φ (m i )(e − m m i ) / r !
G = 2 [ x − 1 + exp( − x )], and x = T / T 0 ,ixi =1

where mi=f(Di) is a mean aberration yield as a function of dose, D, and is expressed by:
1f (D ) = (C + αD + βGD 2 ) exp( −ξD ) + n [1 − exp{ − (γD + δGD 2 )(1 − exp( −ξD ))}] + εξG is G-function of Lea for protracted (chronic) exposure, in which T is time (hours) of dose protraction and T0 is
the mean life time of chromosome breaks (G=1 hour for acute exposure).
The observed distribution of chromosome aberrations is fitted by iteratively re-weighted maximum likelihood
method combined with the bootstrap resampling as shown in the following.
rs 2 = ∑ w i [v i , j (r ) − n i ( r )]2 = mini =0Iteration (i)Bootstrap (j)j=0,1,2,3, , , , , , , ,BTN. (BTN=number of bootstrap resampling). wi is weight, which is in an inverse function ofvariance. Bootstrap samples, vj(r), are obtained by randomized redistribution of residual as are formulated by,v j ( r ) = v ( r ) + ε * , where ε * ∋ ε 0 , ε1, ε2 , ε3 , , , ,The dose distribution profiles thus obtained may be adjusted by lymphocyte survival, S=D/D0. Any D0 values may
be used, but D0=3 Gy in literature is recommended (Edwards et al., Int. J. Radiat. Biol., 38:83-91, 1980). The
equivalent whole body dose (EWBD), exposed fraction (FX) and the dose to the exposed fraction (DX) are given,
respectively.
kEWBD = ∑ φ (m i )D i ,i =1k

F X = ∑ φ (m i ) ,i =1DX =1k∑ φ (m i )DiF X i =1

Dose assessment: Examples
Parameters

Dic+cR+aR

Dic

Dic+cR

Reference dose-response parameters(human G0 lymphocytes for γ-rays in vitro)(C±SE)

8.50E-04

1.85E-04

6.47E-04

1.62E-04

8.50E-04

1.85E-04(α±SE)/Gy

2.31E-02

9.31E-02

1.83E-02

9.95E-03

2.32E-02

4.73E-03

Dic: dicentric. cR: centric ring. aR: acentric ring.

(β±SE)/Gy2

6.41E-02

3.70E-03

5.43E-02

3.95E-03

6.15E-02

3.43E-03(γ±SE)/Gy

1.29E-05

4.38E-06

1.23E-05

4.21E-06

1.26E-05

5.39E-06(δ±SE)/Gy2

3.44E-07

1.00E-07

3.69E-07

9.89E-08

3.96E-07

1.51E-07(ξ±SE)

1.00E-01

1.54E-02

1.02E-01

1.40E-02

1.01E-01

1.91E-02

n181415

A: Mixture of equal volume of whole blood, each irradiated with 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 and 5 Gy γ-rays invitro. Total dose is equivalent to 2.75 Gy. The mixed blood was kept at 37oC for 24 hrs under aeration of 5% CO2
before commencement of culture. B: Victim of Goiania accident. C: Victim of Chernobyl accident. Dose profiles
either (1) unadjusted or (2) adjusted by lymphocyte survival with D0=3 Gy. EWBD: equivalent whole body dose
(Gy). Fx: exposed fraction. Dx: dose (Gy) to the exposed fraction.

C(1)EWBD=2.33±0.16
Fx=1.05±0.05
Dx=2.33±0.16

ϕ(D)
ϕ(D)

Dose, GyEWBD=3.29±0.90
Fx=1.10±0.11
Dx=3.29±0.90

B(2)EWBD=3.06±0.23
Fx=1.05±0.05
Dx=3.06±0.23

ϕ(D)EWBD=2.90±0.15
Fx=1.05±0.05
Dx=2.90±0.15

A(2)

ϕ(D)

B(1)

ϕ(D)

EWBD=2.12±0.22
Fx=1.10±0.11
Dx=2.12±0.22

ϕ(D)

A(1)

EWBD=6.15±3.70
Fx=1.05±0.05
Dx=6.15±3.70C(2)Dose, Gy