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Technical Information Bulletin Document Number: OCAS-TIB-008 

Effective Date: (9/29/2003) Revision No. 0 Page 2 of 5 

Correlation of IMBA calculated doses to ICD-9 Codes 

ICD-9 code Description Surrogate Tissue 

140 Lip HNM* 

141.0-141.5 Tongue HNM* 

141.6 Lingual tonsil LNET 

141.8 & 141.9 Tongue HNM* 

142 Salivary glands HNM* 

143 Gums HNM* 

144 Floor of mouth HNM* 

145 Mouth unspecified sites HNM* 

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* 

160.2 Maxillary sinus HNM* 

160.3 Ethmoidal sinus HNM* 

160.4 Frontal sinus HNM* 

160.5 Sphenoidal sinus HNM* 

160.8 Other HNM* 

160.9 Accessory sinus, unspecified HNM* 

161 Larynx ET2 

162 Trachea, bronchus, and lun g Lung 

163 Parietal (pleura) HNM* 

164.0 Thymus Thymus 

164.1 Heart Heart wall 

164.2-164.9 Mediastinum HNM* 

165 Other and ill-defined sites within the respiratory 

system and intrathoracic organs 

Lung 

* highest non-modeled organ/tissue 
 

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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. 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 biokinetic models are developed on an elemental basis so the 

modeled organs vary with the element of interest. However, the modeled organs also 

include the gastrointestinal tract (ICRP 30) and in the case of inhalation, the respiratory 

tract (ICRP 66). 

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 it originated. 

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

the material deposited in the soft tissue compartments become 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 are 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. For the purposes of 

EEOICPA, t he non-modeled organ with the highest dose is used as the surrogate organ to 

account for this affect in a claimant favorable manner. 

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, it is acceptable in these 

situations to base the dose 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. 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 wit hin 

these regions . The ET2 ’ compartment consists of the material deposited in the fast 
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Technical Information Bulletin Document Number: OCAS-TIB-008 

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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 caus es the 

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

region. S ince 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 co ncept 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 e ffect may not exist in these tissues. 

Tissue associated with the mo uth 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. As a result of this discussion, it is evident 

that 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, they 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 

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 pleura l sacs containing the heart and all the thoracic viscera except 

the lungs. Since these tissues are not within the airways, no direct deposition occurs 
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Technical Information Bulletin Document Number: OCAS-TIB-008 

Effective Date: (9/29/2003) Revision No. 0 Page 5 of 5 

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 tissue s. 

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 

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

Oxford, England. 

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

Cincinnati, Ohio