Effective Quality Factors for Neutrons Based on the Revised ICRP/ICRU

Recommendations

K. G. Veinot1 and N. E. Hertel2

1Y-12 National Security Complex2Georgia Institute of Technology

• Prior to ICRP 60, all dose equivalent quantities were defined in terms of a weighting factor, the quality factor Q(L) – It was applied to the absorbed dose at a point– This weighted absorbed dose was called dose

equivalent

• The ICRP 26 recommendations (1977) brought mean organ dose equivalent

dL Q(L)D H L∫=

( ) dmdLDLQm

HTm L

LT

T ∫ ∫= 1

• ICRP 26 also brought effective dose equivalent

• ICRP 60 introduced a modified concept, the radiation weighting factor wR to compute a quantity called the effective dose

∑=T

TTE HwH

H w DT R T RR

= ⋅∑ ,

E w HT TT

= ⋅∑

0

5

10

15

20

25

1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03

Incident Neutron Energy (MeV)

Rad

iatio

n W

eigh

ting

Fact

ors

• Measurements are performed in terms of ambient dose equivalent and personal dose equivalent.– Still defined in terms of absorbed dose at the reference

point weighted by Q(L)• However, in ICRP 60 the relationship between

Q(L) and L was changed– Reflected higher relative biological effectiveness values

for intermediate-energy neutrons and the reduced effectiveness of heavy ions with L>100 keV/micron

• For types and radiation of energy not included in ICRP 60, the ambient quality factor can be used to obtain wR

Q(L) vs. L

0

5

10

15

20

25

30

35

1 10 100 1000

L (keV/micron)

Q(L

) (Sv

/Gy)

ICRP 60ICRP 26

Ambient Dose Equivalent, H*(d)

• Dose equivalent produced in a sphere with radius of 15 cm of ICRU tissue-equivalent composition at a depth d from an aligned and expanded field

• For penetrating radiations, the depth, d, is taken to be 10 mm.

Personal Dose Equivalent• The Personal Dose Equivalent Hp(d) is

defined under a specified point of the human body (trunk).– ICRU sphere or slab can be used

• To approximate the situation where the location of interest is the trunk of the body, a slab-phantom type geometry is used

• For penetrating radiations, the depth, d, is taken to be 10 mm.

Quality Factors• “The selection of its numerical values

depends not only on appropriate biological data , but also on judgment” (ICRP 92)

• Defined as functions of the unrestricted linear energy transfer (L) in water

• The change in the Q(L) vs. L relationship in ICRP 60 lead to recomputation of H*(10)

Using the kerma Approximation• Below 20 MeV, neutron kerma mostly has been

employed to compute the operational quantities at a depth of 10 mm

• This requires the average quality factors for neutron-induced heavy charged particles be available

( ) ( ) ( )∫=L

LdLELDLQ

DEQ n

nnn

max

min

,1

( ) ( ) ( ) ( ) nnnnnnnnn dE,ErΦEQEkdE,ErH rr =

Qn(En) and qeff(En)• Qn(En) does not include contributions from

neutron-induced photons• Ratio of dose equivalent and absorbed dose

produced by both neutrons and photons is qeff due to a neutron of energy E incident on the phantom

( )( ) ( ) ( ) ( ) ( )

( ) ( ) ( ) ( )∫∫∫∫

+

+=

γγγγγ

γγγγγ

φφ

φφ

dEEEEkdEEEEk

dEEEEkdEEEEkEQE

nnnnn

nnnnnnnx

effq,,

,,

ICRU Recommendations

• Stopping power and range data supplied by In ICRU Report 49 (1993), new data for stopping powers and ranges for protons and alpha particles were published– Chemical binding and phase effects were given careful

consideration– Effects can be substantial

• If stopping power data changes, Q will also change

Operational Quantity Calculations Used in Comparisons in Present Work

FLUKA

MCNP

MCNP

MCNP

Code

No for protonsYes for others

Yes

Yes

Yes

Kerma Approximation

No

Yes

No

No

ICRU 49

YesFerrari and Pelliccioni

1998

YesSiebert and Schuhmacher

1995

YesLeuthold et al. 1992

YesSchuhmacherand Siebert

1992

ICRP 60 Q-L

Slab Dose Equivalent• A 30 cm X 30 cm X 15 cm deep slab

phantom • ICRU tissue equivalent material • Denoted Hp,slab(d,α) where α denotes

angular rotation of the slab phantom in the radiation field.

• For the anterior-posterior (A-P) geometry, Hp,slab(d,α) is equal to Hp,slab(d,0) or simply Hp,slab(d).

Ambient Absorbed Dose Conversion Coefficients –This Work

• Used MCNP4C with ENDF B-VI cross sections• Parallel broad-beam of neutrons centered on the

principal axis of the 15-cm radius ICRU sphere• Tally sphere of radius 0.25 cm centered inside the

ICRU sphere at a depth of 10 mm on the principal axis

• 53-energy bin structure of the International Atomic Energy Agency (IAEA) Compendium

• Energy deposition F6 tally in MCNP

Absorbed Dose Conversion Coefficients – Slab

• Conversion coefficients using a 30 cm X 30 cm X 15 cm ICRU-tissue slab phantom

• Tally volume a 1 cm x 1 cm x 0.1 cm rectangular solid (centered at a 10 mm depth)

Conversion Coefficients

• S(α,β) thermal neutron treatment for light water was used

• Source particles were sampled uniformly within each energy group

• Used the Qn(En) from Siebert andSchuhmacher 1995 and the d(E,En) values computed in this work

Absorbed Dose Conversion Coefficients

1

10

100

1.E-09 1.E-07 1.E-05 1.E-03 1.E-01 1.E+01 1.E+03

Neutron Energy (MeV)

dcc

(pG

y-cm

2 )

dp(10) Present Work

d*(10) Present Work

Conversion Coefficients

1.0E+00

1.0E+01

1.0E+02

1.0E+03

1.0E-09 1.0E-08 1.0E-07 1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00 1.0E+01 1.0E+02

Neutron Energy (MeV)

H(1

0) (

pSv-

cm2)

hp(10) - Present Workh*(10) - Present Workh*(10) - Ferrari and Pelliccioni 1998h*(10) - Siebert and Schuhmacher 1995hp(10) - Siebert and Schuhmacherh*(10) Leuthold et al. 1992Series7

Conversion Coefficients (expanded view)

1.0E+01

1.0E+02

1.0E+03

1.0E-02 1.0E-01 1.0E+00 1.0E+01 1.0E+02

Neutron Energy (MeV)

H(1

0) (

pSv-

cm2)

hp(10) - Present Workh*(10) - Present Workh*(10) - Ferrari and Pelliccioni 1998h*(10) - Siebert and Schuhmacher 1995hp(10) - Siebert and Schuhmacherh*(10) Leuthold et al. 1992h*(1) - Schuhmacher and Siebert 1992

Effective Quality Factors

• hp(10,E) and h*(E) conversion coefficients then used to determine effective quality factors

)()()(

)(EdEd

EhEQ

n

neff

γ

γ

+= +

Effective Quality Factors

0

5

10

15

20

25

1.E-09 1.E-07 1.E-05 1.E-03 1.E-01 1.E+01 1.E+03Neutron Energy (MeV)

Effe

ctiv

e Q

ualit

y Fa

ctor

q*eff(10) - Leuthold et al. 1994qpeff(10) - Present Workq*eff(10) - Present Workq*eff(10) - Ferrari and Pelliccioni 1998wr - ICRP 60

Summary

• No major surprises• ICRP 92 addresses the reconciliation of wR

and the effective quality factor

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.E-09 1.E-07 1.E-05 1.E-03 1.E-01 1.E+01

Neutron Energy (MeV)

q*eff Ratio - Ref.[4] to w R

q*eff Ratio - Present Work to w R