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To: Robert K. Gad III

From: George Chabot

Date: Mar.7, 2003

Subject: Dose from Hot Particle in ExtrathoracicRegion ET2 of Respiratory Tract

As I had observed in my rebuttal testimony, I did not then have time to make a reasonable calculation aimed at

evaluating the effective dose equivalent from inhalation -of a 10 micron diameter hot particle. I did express my

opinion that Dr. Resnikoff's approach, using ICRP-72 dose conversion factors, was not appropriate for

inhalation of a single particle. I also expressed confidence, in my rebuttal testimony, based on my familiarity

with the dosimetry involved, that effective dose equivalent from inhalation of such a particle would be

significantly less than 0.5 mrem. I have since had the opportunity to perform a demonstrative calculation, which

I am including below. Note that I am using the term effective dose, the current analog of effective dose

equivalent, in the analysis, which uses the current ICRP respiratory tract model and tissue weighting factor (for

ET2) as well as the current ICRP dose conversion factors.

The ET2 region, as defined in ICRP Report 66, represents the interior posterior nasal tissues, the pharynx, and

larynx tissues. It was selected as the deposition site for the inhaled 10 micron diameter particle because it

represents the portion of the extrathoracic region that is most subject to cancer induction and has the highest

tissue weighting factor, 0.025. The thoracic region of the respiratory tract was not selected as a deposition site

because of the extremely high probability that a 10 micron particle would not penetrate to the deeper sections of

the tract. The following assumptions and parameter values apply to the dose estimation.

1. The dose equivalent to region ET2 for an adult subject was calculated by assuming an insoluble,

stationary particle residing on the tissue surface for a time period equal to the mean residence time of particles

in region ET2.

2. The mean residence time in ET2 is equal to 0.01 days (14.4 minutes), obtained from the reciprocal of

the removal rate constant of 100 day"' as given in ICRP Report 66. Clearance from the ET2 region is to the GI

tract via swallowing.

3. Total surface area of ET2 region is 450 cm2, as per ICRP 66.

4. Thickness of mucous layer is 15 microns and depth of basal cell target nuclei is 45 microns below

epithelial surface, as per ICRP 66. The combined thickness is 60 microns, 0.006 cm, assumed to be unit density

tissue equivalent material.

5. The dose averaged over all the target tissue area of the ET2 region was calculated for two individual

point isotropic sources, one being Sr-90, with an equilibrium quantity of daughter Y-90 present, chosen because

of its significant potential for delivering dose to basal cells through high energy beta radiation; the second

source was Co-60, selected because of its potential for delivering gamma dose over a greater expanse of tissue

compared to beta radiation.

6. The sources noted in item 5 were individually taken to represent the 10 micron particle source; no self

attenuation of radiation within the source was calculated.

7. The beta dose calculation was done using the VARSKIN MOD2 computer code by assuming the area

of the target tissue could be represented by a disk 450 cm2 in area (radius of 11.97 cm). Dose was evaluated at a

depth of 0.006 cm, based on a 14.4 minute exposure time. The gamma dose component was evaluated,

assuming no photon attenuation and a respective source position 0.006 cm above the 450 cm2 disk.

8. Doses were calculated for nominal 1 microcurie sources and were scaled to provide doses that would

be consistent with the dose calculated by Dr. Resnikoff for his hot particle, taking into account his use of 1

micron AMAD DCFs for his dose determination.

9. Dose resulting from passage of the particle through the GI tract has not been included. This scenario

has previously been investigated by Bechtel/CYAPCO.

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2003 OCT 31 AH : 07

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90Sr VARSKIN results:

90Y VARSKIN results:

Dose averaged over 1 cm2= 1.35 rads

Dose averaged over 450 cm2 = 0.0030 rads

Dose averaged over 1 cm2 = 1.60 rads

Dose averaged over 450 cm2 = 0.0046 rads

Total dose averaged over 450 cm2 = 0.0030 + 0.0046 = 0.0076 rads

Effective dose, E = wTHT (0.025)(0.0076 rads)(1000 mrads/rad)(I mrem/mrad)

= 0.19 mrem.

If a calculation, similar to that done by Resnikoff for his particle, was applied to the Sr-Y particle, an effective

dose would be obtained using the ICRP 72 DCF for Sr-90 (Type M 1 micron AMAD aerosol is recommended

default) as follows:

ElpmAMAD = (3.68xl04 Sv/Bq)(3.7xl 4 Bq/gCi)(I jICi)(10 5 mrem/Sv) = 136 mrem.

The adult dose that Resnikoff calculated for his 12 year decay-corrected particle was 15.7 mrem. Scaling above

results, using this value, we may obtain an adjusted value for effective dose;

E/0.19 mrem = 15.7 mrem/136 mrem, and

E = 0.022 mrem.

60Co VARSKIN results: Beta dose averaged over 1 cm2 = 1.00 rads

Beta dose averaged over 450 cm2 = 0.0022 rads = 2.2 mrem

Gamma dose averaged over 450 cm2 = (7rAT/450) ln((H2+R

3.36x104 rem = 0.336 mrem,

where r = 13.2 rem h-1 mCi' cm2 ,

A= 10 3mCi,

T = 0.24 hours, D

H = 0.006 cm, and 

R = 11.97 cm.

Total dose = 2.2 mrem + 0.34 mrem = 2.54 mrem 3 .a

E = (0.025)(2.54 mrem) = 0.064 mrem.

Again, applying the Resnikoff methodology, based on ICRP-72 DCFs we would obta*n

=

E I pnAMAD = 1Ol 8 Sv/Bq)(3.7xl0 BqfjiCi)(I pCi)(1 05 mremlSv) = 3 7 mrem. 

I;

.- 

I

2 w W

0 ., t

Scaling as previously, we obtain

E/0.064 mrem = 15.7/37, and

E = 0.027 mrem.

Given the above dose estimates, recognizing simplifications in the dose calculation, especially as related to

receptor geometry, I would judge that it would be extremely unlikely that the effective dose to any individual

from inhalation of a single 10 jim diameter particle, of the approximate type described by Resnikoff, would

exceed 0.5 mrem (excluding contribution from passage through GI tract).