Office of Compensation Analysis and Support 

Technical Information Bulletin

Document Number: OCAS-TIB-008

Effective Date: (10/04/2007)

Revision No. 1

Use of ICRP 66 to Calculate Respiratory Tract Doses Page 1 of 6 

Approval:_______Signature on File__ Date: __10/04/2007_ J.W. Neton, OCAS Health Science Administrator Supersedes: Revision 0 

RECORD OF ISSUE/REVISIONS 

ISSUE 

AUTHORIZATION 

DATE 

9/29/2003

EFFECTIVE 

DATE 

9/29/2003 

REV. NO. 

0 

DESCRIPTION 

New document to provide guidance on the use of 

ICRP 66 to calculate respiratory tract doses. 

10/04/2007 10/04/2007 1 Revision in response to review by ABRWH to 

clarify instructions and add reference to ICRP 

100. 

1.0 PURPOSE

This Technical Information Bulletin provides guidance on selecting an appropriate tissue 

to serve as the surrogate for the internal dose to specific organs/tissues associated with or 

near the respiratory tract. 

2.0 Background

The International Commission on Radiological Protection (ICRP) human respiratory tract 

model (ICRP 66) and human alimentary tract model (ICRP 100) provide methods for 

calculating organ and tissue doses resulting from intakes of radioactive material. Under 

EEOICPA, the dose to a particular tissue must be estimated. While some tissues may fall 

within the physical boundaries of a region described by ICRP 66 (e.g. ET1, ET2), they do 

not necessarily share the same physical characteristics of the major tissues in that region. 

This TIB designates the appropriate ICRP calculated organ/tissue dose to use for the 

various ICD-9 coded cancers associated with the respiratory tract. 

3.0 Guidance

The following table correlates ICD-9 codes to IMBA calculated organ doses. The ICD-9 

codes have been broken up to the extent necessary to designate an appropriate ICRP 

region. Regions labeled HNM or PROX designate the use of the highest non-modeled 

organ or the use of a non-modeled organ in proximity to the organ of interest. A 

discussion of this term is included in section 4.0 of this bulletin. The remaining regions 

are described by the term used in IMBA. When the appropriate choice was not clear, the 

more claimant favorable choice was selected. 
Office of Compensation Analysis and Support

Technical Information Bulletin Document Number: OCAS-TIB-008

Effective Date: (10/04/2007) Revision No. 1 Page 2 of 6 

Correlation of IMBA calculated doses to ICD-9 Codes 

ICD-9 code Description Surrogate Tissue 

140 Lip HNM* or PROX** 

141.0-141.5 Tongue HNM* or PROX** 

141.6 Lingual tonsil LNET 

141.8 & 141.9 Tongue HNM* or PROX** 

142 Salivary glands HNM* or PROX** 

143 Gums HNM* or PROX** 

144 Floor of mouth HNM* or PROX** 

145 Mouth unspecified sites HNM* or PROX** 

146.0 Tonsil LNET 

146.1 Tonsillar fossa LNET 

146.2 Tonsillar pillars LNET 

146.3-146.9 Oropharynx ET2 

147 Nasopharynx ET2 

148 Hypopharynx ET2 

149.0 Pharynx, unspecified ET2 

149.1 Waldeyer's ring LNET 

149.8 Other ET2 

149.9 Ill-defined ET2 

160.0 Nasal cavity ET1 

160.1 Auditory tube, middle ear, and mastoid air cells HNM* or PROX** 

160.2 Maxillary sinus HNM* or PROX** 

160.3 Ethmoidal sinus HNM* or PROX** 

160.4 Frontal sinus HNM* or PROX** 

160.5 Sphenoidal sinus HNM* or PROX** 

160.8 Other HNM* or PROX** 

160.9 Accessory sinus, unspecified HNM* or PROX** 

161 Larynx ET2 

162 Trachea, bronchus, and lung Lung 

163 Parietal (pleura) HNM* or PROX** 

164.0 Thymus Thymus 

164.1 Heart Heart wall 

164.2-164.9 Mediastinum HNM* or PROX** 

165 Other and ill-defined sites within the respiratory 

system and intrathoracic organs Lung 

* highest non-modeled organ/tissue 

** non-modeled organ/tissue in proximity to organ of interest 
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Technical Information Bulletin Document Number: OCAS-TIB-008

Effective Date: (10/04/2007) Revision No. 1 Page 3 of 6 

4.0 Discussion

4.1 Highest non-modeled organ

The dose estimate for a number of tissues is based on the highest non-modeled organ 

dose, designated as HNM in the table, or on the dose to a non-modeled organ in 

proximity to the organ of interest, designated as PROX in the table. For the purposes of 

this document, non-modeled organs are those in which the transfer of material to and 

from the organ is not specifically modeled by the ICRP. The modeled organs include the 

alimentary tract and in the case of inhalation, the respiratory tract. 

Many of the current biokinetic models contain soft tissue compartments. These 

compartments account for the material deposited in all the organs not specifically 

accounted for in the biokinetic model. The energy emitted as alpha and beta radiation is 

generally assumed to be deposited in the tissue where it originated. However, photons 

can irradiate other tissues as well as the tissue from which they originated. 

Therefore, when the energy emitted by a radionuclide is primarily alpha or beta radiation, 

the material deposited in the soft tissue compartments becomes the primary source of 

dose to these non-modeled organs. This causes most of the non-modeled organs to 

receive the same dose. For radionuclides where the energy of the photon emissions is a 

substantial fraction of the emitted energy, the cross-irradiation from material deposited in 

other tissues can become a significant portion of the dose to organs. This causes the dose 

received by non-modeled organs to vary from one organ to the next. 

It is conceivable that a situation could arise where a photon emitting radionuclide causes 

a large difference in doses delivered to non-modeled organs. In accordance with the 

Internal Dose Reconstruction Implementation Guideline, in these situations the dose 

should be based on an organ that is not the highest non-modeled organ. The choice in 

these cases should be based on the proximity of the surrogate organ to the organ of 

interest. 

4.2 Mouth, Nose and Throat

ICRP 66 describes the ET2 region as containing the posterior nasal passage, the 

oropharynx, the larynx, and the mouth. ICRP 100, Annex E, “Consistency Between the 

HATM (Human Alimentary Tract Model) and the HRTM (Human Respiratory Tract 

Model),” explains further: 

The HRTM assumes that deposition in the ET airways of inhaled particles 

that enter the respiratory tract through the mouth only takes place in the 

larynx. Similarly deposition in the ET airways of inhaled particles that 
Office of Compensation Analysis and Support

Technical Information Bulletin Document Number: OCAS-TIB-008

Effective Date: (10/04/2007) Revision No. 1 Page 4 of 6 

enter through the nose is assumed to take place in the nasal passages and 

in the larynx...Hence, as the HRTM assumes no deposition of particles in 

the oral cavity and there is no clearance of activity deposited elsewhere in 

the oral cavity, the oral cavity can be removed from region ET2 and 

compartment ET2 without any effect on clearance, or the number of 

transformations taking place in the ET airways. 

This region is further broken down into compartments ET2’ and ETseq (ICRP did not 

differentiate the ET2 region from the ET2 compartment which is denoted here as ET2’) 

which represent different tissue types within these regions. The ET2’ compartment 

consists of the material deposited in the fast moving mucus. This represents the majority 

(99.95%) of the material deposited in this region. The ETseq compartment represents the 

small amount of material sequestered near the basal cell layer. This material clears at a 

slow rate to the lymphatic system. 

The slow clearance of the ETseq compartment results in a much higher number of 

disintegrations in this compartment than in the ET2’ compartment. This causes the 

ETseq compartment to always be the major dose contributing compartment to the ET2 

region. Since the ET2 dose primarily results from disintegrations within the ETseq 

compartment, the use of the ET2 dose as a surrogate for other tissues of the mouth, nose 

and throat depends on the applicability of the assumptions associated with the ETseq 

compartment to the tissue of interest. 

The sequestering of material in the ETseq compartment is addressed in paragraph E98 of 

ICRP 66. This paragraph indicates that this concept was based on animal studies of the 

posterior nasal passage. The paragraph goes on to indicate that the oropharynx, and the 

larynx are a different type of tissue and therefore this effect may not exist in these tissues. 

Tissue associated with the mouth was not addressed. The ICRP decided to assign the 

ET2 dose to the other tissues (oropharynx, and the larynx) indicating this would be an 

overestimate of the dose for alpha emitters. The mouth was not considered in assessing 

the dose to the ET2 region and therefore should be treated as unmodeled tissue. 

Unmodeled tissue is assessed in accordance with section 4.1 normally by using the 

highest non-modeled organ dose. Even though the ICRP indicated the dose to the 

oropharynx and the larynx would be overestimated by using ET2, it specifically indicated 

that ET2 should be used to assess the dose to these tissues. For that reason, the dose to 

these two regions will be assessed using the ET2 dose. 

4.3 Lung Dose

ICRP 66 determines lung dose by calculating the dose to several distinct regions within 

the lung and taking the weighted average of these regions. Ideally, the estimated dose to 
Office of Compensation Analysis and Support

Technical Information Bulletin Document Number: OCAS-TIB-008

Effective Date: (10/04/2007) Revision No. 1 Page 5 of 6 

the actual tissue that developed cancer would be the correct dose to use for the purposes 

of EEOICPA. However, the tissues used in the ICRP model are seldom indicated in a 

claimant’s diagnosis of respiratory-related cancer. Indeed, the ICD-9 codes themselves 

do not separate these tissues. Because of this, the most appropriate dose to use for lung 

cancers is the dose designated by ICRP as the thoracic dose. This dose is listed in the 

output of IMBA as the “Lung” dose. 

4.4 Pleura and Mediastinum Dose

The pleura consists of the membranes surrounding the lungs. The Mediastinum is the 

region between the pleural sacs containing the heart and all the thoracic viscera except 

the lungs. Since these tissues are not within the airways, no direct deposition occurs 

within these tissues. Also, these tissues are not associated with the removal of the 

deposited material. Consequently, the dose to these tissues is best estimated using the 

soft tissue compartments of the particular biokinetic model. Because of their close 

proximity to the lungs, significant cross-irradiation dose from material deposited in the 

lungs would cause the dose to these tissues to be one of the highest non-metabolic organ 

doses. This should be accounted for by the convention of using the highest nonmetabolic organ dose to estimate the dose to these tissues. 

5.0 References

1. Department of Health and Human Services (1991) The International 

Classification of Diseases Clinical Modification (9th Revision) Vol. I&II, 

Department of Health and Human Services Publication No. (PHS) 91-1260, 

U.S. Government Printing Office, Washington D.C. 

2. ICRP, (1979) International Commission on Radiological Protection. Limits for 

Intakes of Radionuclides by Workers, Part 1, ICRP Publication 30, Annals of 

the ICRP Vol. 2 (3/4), Pergamon Press, Oxford, England. 

3. ICRP, (1994) International Commission on Radiological Protection. Human 

Respiratory Tract Model for Radiological Protection, ICRP Publication 66, 

Annals of the ICRP Vol. 24 (1-3), Pergamon Press, Oxford, England. 

4. ICRP, (1994) International Commission on Radiological Protection. Agedependent Doses to Members of the Public from Intake of Radionuclides, Part 

2, ICRP Publication 67, Annals of the ICRP Vol. 23 (3/4), Pergamon Press, 

Oxford, England. 

5. ICRP, (1995) International Commission on Radiological Protection. Agedependent Doses to Members of the Public from Intake of Radionuclides, Part 
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Technical Information Bulletin Document Number: OCAS-TIB-008

Effective Date: (10/04/2007) Revision No. 1 Page 6 of 6 

3, ICRP Publication 69, Annals of the ICRP Vol. 25 (1), Pergamon Press, 

Oxford, England. 

6. ICRP, (2006) International Commission on Radiological Protection. Human 

Alimentary Tract Model for Radiological Protection, ICRP Publication 100, 

Annals of the ICRP Vol. 36 (1-2), Pergamon Press, Oxford, England. 

7. NIOSH, (2002) Internal Dose Reconstruction Implementation Guideline, OCASIG-002, Rev 0. National Institute for Occupational Safety and Health, 

Cincinnati, Ohio