1. ASSESSMENT OF OCCUPATIONAL EXPOSURE DUE TO INTAKE OF RADIONUCLIDES
Biokinetic Models

2. Biokinetic Models - Unit Outline
Ingestion
Entry through Wounds and Skin
Systemic Activity
Excretion

3. Ingestion

4. Ingestion - Gastrointestinal tract model
ICRP 30 model has 4 compartments,
Stomach,
Small intestine,
Upper large intestine and
Lower large intestine
Uptake to blood in the small intestine - specified by fractional uptake (f1) values
The model used for the BSS to describe the behaviour of radionuclides ingested by workers is that given in ICRP Publication 30. It has four compartments, representing the stomach, the small intestine, the upper large intestine and the lower large intestine. The mean residence times in the gastrointestinal tract compartments are 1, 4, 13, and 24 h respectively. The uptake to blood takes place from the small intestine and is specified by fractional uptake (f1) values. The only changes to the model parameters for the calculation of the dose coefficients for workers given in the BSS compared to those given in ICRP Publication 30 were to some of the f1 values.

5. Gastrointestinal tract model ICRP 30
Ingestion
Stomach (ST)
Small intestine (SI)
Upper large intestine (ULI)
Lower large intestine (LLI)
Faecal Excretion
Body fluids
ST B
LLI
ULI
SI
The gastrointestinal tract is represented by four sections. Each section is considered as a single compartment and translocation from one compartment to the next is assumed to be governed by first order kinetics. The rate constants, λ, for transfer between compartments are given in this table. In this model, the small intestine (SI) is assumed to be the only site of absorption from the gastrointestinal tract to body fluids. The rate constant, λB, for transfer of activity to systemic body fluids can be estimated from f1, the fraction of the stable element reaching body fluids following ingestion.
Transfer constant,
 = 1/residence time
All tabulated values for ingestion
are based on this model

6. New Human Alimentary Tract (HAT) model - ICRP 100
ICRP 60 introduced specific risk estimates and wT for radiation-induced cancer of the oesophagus, stomach and colon
Dose estimates needed for each region
ICRP 30 model:
Did not include the oral cavity or the oesophagus
Treated the colon as two regions - upper and lower large intestine.
The alimentary tract comprises the oral cavity, including the mouth, teeth, salivary glands and pharynx, the oesophagus, the stomach, the small intestine, including duodenum, jejunum and ileum, the large intestine, including ascending, transverse and descending colon, rectum and anal canal.
The revision of the Publication 30 model for the alimentary tract is motivated by a number of developments. First, the 1990 recommendations of ICRP introduced specific risk estimates and tissue weighting factors, wT for radiation-induced cancer of the oesophagus, stomach and colon, requiring dose estimates for each of these regions. The publication 30 model did not include the oral cavity or the oesophagus and treated the colon as two regions - upper and lower large intestine.

7. New HAT model ICRP 100 /2
Considerable data is now available on material transit times through the different regions of the gut using non-invasive techniques
Information has become available on the location of the sensitive cells and retention of radionuclides in different regions
New data includes
Differences between solid and liquid phases
Age and sex related differences
Effect of disease conditions
Since the development of the ICRP Publication 30 model, a considerable body of data has become available on the transit of materials through the different regions of the gut. These data have been obtained using non-invasive, mainly scintigraphic techniques and include studies of differences between solid and liquid phases, age and sex related differences and the effect of disease conditions.

8. New HAT model ICRP 100 /3 Data are being used:
to determine default transit rates for the defined regions of the alimentary tract
for the 6 age groups given in ICRP 56
New information:
For morphometrical and physiological parameters,
On the location of sensitive cells and in different regions of the alimentary tract
These data are being used to determine default transit rates for the defined regions of the alimentary tract for the six age groups given in ICRP Publication 56. Information has become available for morphometrical and physiological parameters and on the location of sensitive cells and in different regions of the alimentary tract. More information has become available concerning absorption, retention and transfer from different parts of the alimentary tract. Extensive age-, sex- and health-dependent information is available that will be included in the new model.

9. Anatomy and physiology of HAT
Primary functions
To move the food
Digestive function
Absorptive function
Excretion function via liver and biliary tract.
Additional functions
Defensive functions to protect the body from colonization by bacteria
Contains microbial population that produces vitamins
These data are being used to determine default transit rates for the defined regions of the alimentary tract for the six age groups given in ICRP Publication 56. Information has become available for morphometrical and physiological parameters and on the location of sensitive cells and in different regions of the alimentary tract. More information has become available concerning absorption, retention and transfer from different parts of the alimentary tract. Extensive age-, sex- and health-dependent information is available that will be included in the new model.

10. Anatomy and physiology of HAT
Overall structure
Detailed structure of different epitelia
Oral cavity, pharynx, oesophagus
Stomach, small and large intestines
Villi and crypts structure in small intestine
These data are being used to determine default transit rates for the defined regions of the alimentary tract for the six age groups given in ICRP Publication 56. Information has become available for morphometrical and physiological parameters and on the location of sensitive cells and in different regions of the alimentary tract. More information has become available concerning absorption, retention and transfer from different parts of the alimentary tract. Extensive age-, sex- and health-dependent information is available that will be included in the new model.

11. Structure of the HAT Model – ICRP 100
Deposition and retention on teeth.
Entry per ingestion, from Respiratory Tract
Deposition in oral mucosa or wall of the Stomach and intestine
Transfer back from the oral mucosa or walls of ST and intestine back in the lumen
Transfer from various secretory organs or blood into the contents of certain segments of HAT.

12. Main differences with previous model /1
Oral cavity not present in the ICRP30 model
In ICRP30 model the division of large intestine is in only 2 regions : ULI and LLI. (in HATM there are 3 regions for the colonic transit)
The ICRP30 model takes into account only decays of the radionuclide occurring during transit. In HATM it has been taken into account also transformations of the radionuclide due to retention in tissues.

13. Main differences with previous model /2
In ICRP30 model absorption of a radionuclide is supposed to occur only in Small intestine. HATM includes pathways to account for absorption from :
Oral mucosa
Stomach,
Specific segment of colon
HATM provides age- and gender-specific transit times for all segments of the tract and for the upper segments (oral cavity, oesophagus and stomach) it provides also material specific transit times.

14. Transit times
Extremely large deviation from the norm can be found from constipation or diarrhoea, unusual diet or pharmaceuticals which can affect the actual transit times.
So the default transit times may not be appropriate for individual specific applications.
Uncertainties and variability in transit times are reported in ICRP 100.
Within a first-order kinetics a transit time of T days corresponds to a transfer coefficients of 1/T per day (d-1)
The review of data has been done for the transit times of all segments of HAT.

15. Transit times and tranfer coefficients for Adult Males
ORGAN
TRANSIT TIMES
TRANSFER COEFFICIENTS
1/T
(d-1)
Mouth
Total diet
12 s
7200
Oesophagus
Fast Slow
90% %
7 s s
Stomach
70 min
20.57
Small Intestine
4 h 6
Right Colon
12 h 2
Left Colon
Recto sigmoid

16. Absorption from content of HAT
Even if the absorption predominantly took place in the small intestine, provision is made for the inclusions of components of absorption from
oral cavity,
stomach or
any segment of the colon.
Absorption from any other segment of the alimentary tract is depicted as transfer from the contents to the wall of that segment, followed by transfer to blood in the portal vein to entry into the general circulation.

17. Absorption from content of HAT / 2
In the planned ICRP reports that will recommend the use of the HATM for a range of elements, information for each element will be given in terms of fractional absorption, replacing the f1 values of Publication 30 (ICRP, 1979) with fA values.
Thus, fA denotes total absorption to blood in the HATM and represents the fraction of the material entering the alimentary tract.
It is given by the sum of the fractions of the material entering the alimentary tract, fi, absorbed in all of the regions of the alimentary tract:

18. Absorption from content of HAT / 3
In the majority of cases, information will only be available on the total absorption of the element and its radioisotopes to blood with no information on regional absorption. As in the Publication 30 model the standard assumption will be that this absorption takes place entirely from the small intestine so fSI=fA.
On the contrary if an element is known to be absorbed from the stomach as well as from the small intestine, values of fST and fSI would be specified, where:

19. Absorption from content of HAT / 4
For the implementation of the HATM in the absence of absorption from retention in the walls, teeth and oral mucosa, the following transfer coefficient li,B applies for the uptake to blood from compartment i of the HATM.
Where fi is the fraction of then intake assumed to be absorbed from compartment i and li,i+1 is the transfer compartment to the next compartment i+1.

20. Absorption from content of HAT / 5
In the most common case with the absorption only from the small intestine to the blood the transfer coefficient is given by lSI,B is given by
Where lSI,RC is the coefficient for transfer from the small intestine to the right colon (6 d-1).

21. Absorption from content of HAT / 6
In the case of an absorption also from the stomach fST, the transfer coefficient for uptake from the stomach is given by lST,B is given by
Where lST,SI is the coefficient for transfer from the stomach to the small intestine (20.57 d-1 for adults and total diet). In this case case the transfer coefficient for uptake from the small intestine ( lSI,B ) is given by:

22. Dosimetry of HAT
Geometric model for the calculation of SEE values for the tubulus part of the HATM

23. Dosimetry of HAT / 2
Geometric model for the calculation of SEE values for the epitelial lining of the small intestine

24. Dosimetry of HAT / 3
Depth of target cells in the different sub-regions of the HATM, in adult male.
The target cells are always the epithelial stem cells.
For some alpha and beta emitters this change in respect to ICRP30 model and substantially reduced dose estimates as the alpha or beta emissions originating in the content of the HAT do not penetrate the depth at which the sensitive cells are thought to reside.

25. Dosimetry of HAT / 4
Comparison in SAF values (g-1) from ICRP 30 and HATM for the lumen of stomach in adult male. (in function of electron energy ).

26. Dosimetry of HAT / 5
Comparison of committed equivalent doses and E(50) for Ru-106 and Pu-239 after ingestion, using HATM and ICRP 30 models.

27. Dosimetry of HAT / 6
For the dose to the organ “colon” the mass weighted mean of the dose coefficients of the 3 sections of the colon i.e. (this implies that the relative risk of radiation effects is not significantly different in these 3 regions)
For the time being no calculation has already been performed with the HATM as the values of fA have not been indicated by ICRP for the different elements.

28. Entry through Wounds and Skin

29. Entry through wounds
Much of the material may be retained at the wound site, however
Soluble material can be transferred to other parts of the body via blood
Insoluble material translocated slowly to regional lymphatic tissue
Gradually dissolves and eventually enters the blood
Some insoluble material can be retained at the wound site or in lymphatic tissue for life
May need to excise contaminated tissues.
Entry through wounds and through intact skin are additional pathways by which radionuclides can enter the body. Although much of the material may be retained at the wound site, soluble material can be transferred to the blood and hence to other parts of the body. Insoluble material will be slowly translocated to regional lymphatic tissue, where it will gradually dissolve and eventually enter the blood.

30. Entry through wounds. Soluble materials
Soluble materials may translocate from the wound site to the blood
Translocation rate depends on solubility
Distribution of the soluble component similar to material entering blood from lungs or GI, however
Some exceptions for radionuclide chemical forms entering blood directly
If the materials are soluble, then they may translocate from the wound site to the blood at a rate which depends on their solubility. The distribution of this soluble component will, in most instances, be similar to that of material entering the blood from the lungs or gastrointestinal tract, but there may be exceptions for some chemical forms of radionuclides which enter the blood directly.

31. Wound model History
In the past ICRP and NCRP both developed a respiratory tract model in parallel
- About 10 years ago they agreed to share tasks to develop biokinetic models
- ICRP: Human Alimentary Tract Model (ICRP 100)
- NCRP: Wound Model
- Both committees had representation from both organisations

32. Announced Biokinetic NCRP Wound Model

33. The SOLUBLE Model
4 types of “Soluble” compounds have been indicated by NCRP :
Avid
Strong
Moderate
Weak
related to the persistent retention in the wound site (chemical behavior)

34. Retention at the wound site for
soluble materials

35. The COLLOID Model
As difference from soluble materials the grouping of insoluble materials in wound are based on the physical properties of the deposited material.
The three categories indicated by NCRP are Colloid, Particle and Fragment.

36. The PARTICLE Model
In this model particles with diameter less than 20 micrometers are considered

37. Characteristics of the Wound Model
- Input material-specific due to its physical and chemical state: soluble, colloids, particles (≤ 20 µm), fragments (> 20 µm)
- Soluble material may become insoluble due to hydrolysis and vice versa
- Release from the wound site to blood (soluble materials) and lymph nodes (particles)
- 4 retention classes for soluble material: weak, moderate, strong and avid due to retention after 1, 16, and 64 d.

38. Values of parameters in NCRP wound model

39. Status of NCRP wound model
- A set of final transfer rates is given for all 7 default categories
- It will be published soon as NCRP report.
- No dosimetric parameters for wound sources.
- ICRP will adopt this model; the revision of ICRP Publication 30/54/68/78 will contain wound information.

40. Entry through intact skin
Several materials can penetrate intact skin
Tritium labeled compounds,
Organic carbon compounds and
Compounds of iodine,
A fraction of these activities enter the blood
Specific models need to be developed to assess doses from such intakes, e.g. behavior of tritiated organic compounds (OBT) after direct absorption is quite different from that after inhalation or ingestion
A number of materials, such as tritium labelled compounds, organic carbon compounds and compounds of iodine, can penetrate intact skin. In these cases, a fraction of the activity will enter the blood. Specific models need to be developed to assess doses from such intakes. For example, the behaviour of tritiated organic compounds following direct absorption through the skin will be significantly different from that after inhalation or ingestion.

41. Entry through intact skin
Both the equivalent dose to the contaminated area and the effective dose need to be considered after skin contamination.
ICRP biokinetic models can only be used for the calculation of the effective dose arising from the soluble component, once the systemic uptake has been determined.
For skin contamination, both the equivalent dose to the area of skin contaminated and the effective dose will need to be considered. The biokinetic models developed by the ICRP can only be used for the calculation of the effective dose arising from the soluble component, once the systemic uptake has been determined.

42. Systemic Activity

43. Uptake
The fraction of an intake entering the systemic circulation is referred to as the uptake
ICRP models for radionuclides in systemic circulation are used to calculate dose coefficients
Following review of data behavior of radionuclides in the body, a number of elemental models have been revised
Revised models were also used to calculate dose coefficients for workers
The fraction of an intake entering the systemic circulation is referred to as the uptake. For the calculation of the dose coefficients in the BSS, the models recommended by the ICRP were used to describe the behaviour of radionuclides that have entered the systemic circulation. As a result of a review of data available on the behaviour of radionuclides in the body, the models recommended for a number of elements in ICRP Publication 30 have been revised, as described in Publications 56, 67, 69 and 71. These revised models were also used in the calculation of the dose coefficients for workers given in the BSS.

44. Revision of systemic models
Models for several elements have been revised, particularly to account for recycling of radionuclides between compartments (so they are more complicated!)
The model are more physiologically oriented, can be applied to calculate bioassay quantities, and evaluate dose to the general population not only to workers.
Previously, a number of radionuclides (e.g. 239Pu) were assumed to be retained on bone surfaces - a conservative assumption
Evidence indicates a fraction of plutonium is buried as a result of bone growth and turnover
A number of the revised systemic models for adults retain the model structure given in ICRP Publication 30, but with minor changes to the distribution of radionuclides between body compartments and the retention functions. In addition, the models for a number of elements have been extensively revised, in particular to take account of recycling of radionuclides between compartments. In ICRP Publication 30, a number of radionuclides (e.g. 239Pu) were assumed to be ‘bone surface seekers’, i.e. to be retained on bone surfaces. This was known to be a conservative assumption, particularly for alpha emitting radionuclides. Evidence from animal studies and human data indicate that a fraction of plutonium becomes buried as a result of bone growth and turnover.

45. Revision of systemic models/2
Another fraction is desorbed and re-enters the blood
Some may be re-deposited in the skeleton and liver or be excreted
In contrast, ‘bone volume seeking’ nuclides, such as 90Sr and 226Ra, have been assumed to instantaneously distribute in bone volume
A further fraction of the plutonium is desorbed from the bone and re-enters the blood. Of this, some may be redeposited in the skeleton and liver or be excreted. In contrast, ‘bone volume seeking’ radionuclides, such as Sr-90 and Ra-226, were assumed in Publication 30 to be instantaneously distributed throughout the bone volume.

46. Revision of systemic models/3
The process is actually progressive
Generic models for plutonium, other actinides, and for the alkaline earth metals have been developed to:
Allow for the known radionuclide behavior
Account for knowledge of bone physiology
The model for alkaline earth metals has also been applied, with some modifications, to lead and to uranium.
In practice, the process is progressive, although it occurs more rapidly than for bone surface seeking radionuclides such as plutonium. To allow for the known behaviour of radionuclides and to take account of present knowledge of the physiology of bone, generic models for plutonium and other actinides (Cm, Am, Np and Th) and for the alkaline earth metals (Ca, Sr, Ba and Ra) have been developed. The model for alkaline earth metals has also been applied, with some modifications, to lead and to uranium.

47. Revision of systemic models: generic model
The ICRP has issued new biokinetic models that have been developed for selected radionuclides since the issue of Publication 30. In the cases of hydrogen, cobalt, ruthenium, caesium, and californium, systemic models are taken to be simple linear chains of compartments similar to the models given in ICRP Publication 30. A generalised model for these elements, addressing intake by inhalation, ingestion, and transfer to systemic body fluids, is illustrated in this slide.
Two generic physiologically-based models have been developed. One is applied for strontium, radium, and uranium; the other for thorium, neptunium, plutonium, americium, and curium. These are briefly described in the following. Special models have also been developed for iron and iodine.

48. Non-recycling generic model

49. Iodine Description (from ICRP 67) Of iodine that reaches the blood :
a fraction equal to 30% is accumulated into the thyroid gland,
a fraction of 70% is excreted directly in urine.
The biological half life in blood is taken as 0.25 d.
Iodide incorporated into thyroid hormones leaves the gland with an half time of 80 d and enters other tissues where it is retained with a half-time of 12 d.
Most iodide (80%) is subsequently released and is available in the circulation for uptake in the gland and urinary excretion.
The remainder (20%) is excreted in faeces in organic form.

50. Iodine
Model :
ULI
LLI

51. Iodine
Age-dependent parameters

52. Caesium Description (from ICRP 67)
Systemic caesium is taken to be distributed uniformly throughout all body tissues
10% of activity is assumed to be retained with a biological half life of 2 days (A)
90% of activity is assumed to be retained with a biological half life of 110 days (A)
For female the half time of compartment B is significantly less than for males.
In some countries there is also evidence of mean biological half time for adult males shorter than 110 d.
Urinary to faecal excretion ratio of 4:1 is recommended.

53. Caesium
Model :

54. Caesium
Age-dependent parameters :

55. Partitioning between urine and faeces

56. Skeleton
Bone formation is made by bone-forming cells (osteoblasts). They synthesise the organic matrix and perform mineralisation. This results in a hard, durable structure (not permanent).
Throughout life there is a continual modification (remodelling) of bone by bone-resorbing cells (osteoclasts).
Two types of bone structures :
CORTICAL BONE (Compact)
TRABECULAR BONE (Spongy, Cancellous)

57. Skeleton Cortical Bone Trabecular Bone Hard, dense bone
Forms the outer walls of bones
The bulk of compact bone is found in shafts of long bones (e.g. femur)
Trabecular Bone
Soft, spongy bone
Forms the interior parts of flat bones and of end long bones
It has much higher porosity than compact bone and soft tissue content (bone marrow).

58. Skeleton
Figure related to the head of human femur (ICRP 70)

59. Skeleton
Figure of bones in humans (ICRP 70)
Skull is about 14-15% (around 1/7) of the mass of all bones.

60. Skeleton
Percentages of cortical and trabecular tissues in bones (ICRP 70)

61. Model for Sr, Ra and U
The alkaline earth element strontium and radium, follow the movement of calcium in the body but exhibit different rates of transfer from that of calcium due to discrimination by biological membranes and bone mineral. Both elements have similar skeletal uptake and distribution at early times after injection, and, within a few months, nearly all the total-body activity is associated with bone mineral. The same general model with suitable modification is used for uranium, because of its similar behaviour.
Activity entering blood (plasma) from the respiratory tract or gastrointestinal tract is retained by bone and soft tissues or excreted in the urine and faeces. All activity leaving the soft tissue compartments is assumed to be returned to plasma. Activity returned to plasma is assumed to be redistributed among tissues and excreta according to the same parameter values as for the original input to plasma.
Bone is divided into cortical and trabecular components, each of which is further divided into bone surface and bone volume. Rapidly exchangeable activity in bone is assumed to reside on bone surface, which is treated as a uniformly mixed compartment that exchanges activity with blood plasma. Bone volume is assumed to consist of two sub-compartments, representing relatively exchangeable activity and relatively non-exchangeable activity. These compartments are denoted by EXCH and NONEXCH, respectively.

62. Model for Sr, Ra and U/2
Skeletal activity first deposits on bone surfaces
Return to plasma or migrates to exchangeable bone volume within a few days
Some activity leaves exchangeable bone volume is assumed to return to bone surfaces
Remainder is assigned to non-exchangeable bone volume
Gradually moves to plasma by bone resorption
Activity entering the skeleton is assumed to deposit initially on bone surfaces but to return to plasma or migrate to exchangeable bone volume within a few days. A portion of activity leaving exchangeable bone volume is assumed to return to bone surfaces and the rest is assigned to non-exchangeable bone volume from which it is gradually removed to plasma by bone resorption.

63. Model for Sr, Ra and U/3
Soft tissue is represented by 3 compartments, ST0, ST1, and ST2
For radium and uranium, the liver is kinetically distinct from other soft tissues
Excretion of U through the kidney and exchange of activity between plasma and kidney tissues is also considered
For all three elements soft tissue is represented by three compartments, ST0, ST1, and ST2. In the cases of radium and uranium the liver is taken to be kinetically distinct from other soft tissues. For uranium, excretion through the kidney and exchange of activity between plasma and kidney tissues is also considered.
The model is intended to provide reasonably accurate predictions of the time-dependent activity on bone surfaces and bone volume and rates of excretion after transfer into systemic body fluids of isotopes of strontium, or radium and uranium into plasma, using a minimal number of compartments and first-order transfer between compartments.

64. Model for Th, Np, Pu, Am and Cm
The skeleton is divided into cortical and trabecular regions, and each of these is subdivided into bone surfaces, bone volume, and bone marrow. Activity entering the skeleton is assigned initially to bone surfaces and is subsequently transferred to bone marrow by bone resorption or to bone volume by bone formation. Activity in bone volume is transferred to bone marrow by bone resorption. Activity is removed from bone marrow to blood over a period of months and is redistributed in the same pattern as the original input to blood.
Blood is treated as a uniformly mixed pool. Compartment ST0 is a soft tissue pool that includes the extracellular fluids and exchanges material with blood over a period of hours or days. Soft tissue compartments ST1 and ST2 are used to represent intermediate-term retention (up to 2 years) and tenacious (many years), respectively, in the ‘massive soft tissues’ (muscle, skin, subcutaneous fat, and all other soft tissues not explicitly included in other compartments of the model).

65. Model for Th, Np, Pu, Am and Cm/2
Th and Pu retention and
excretion data are most
easily reproduced using
a 2 compartment model
Liver 2 represents
retention with t½ > 1 year
Liver 1 loses a portion of its activity to the GI tract over a relatively short period (1 year)
Liver 2 shows greater retention of Pu
GI tract
contents
Blood
Liver 1
Liver 2
Faeces
Depending on the element, the liver is viewed as a single compartment, indicated as Liver 1, or two compartments, with the second compartment indicated as Liver 2. Liver 2 represents relatively tenacious retention (t½ > 1 year) which is defined on a kinetic rather than a biological basis. Data on hepatic retention and faecal excretion of thorium and plutonium are most easily reproduced using a two-compartment liver model, with one compartment losing a portion of its activity to the gastrointestinal tract over a relatively short period (1 year) and the second showing greater retention of plutonium (many years).

66. Model for Th, Np, Pu, Am and Cm/3
Am and Cm  Liver can
be treated as a uniformly
mixed pool, losing activity
to blood and the GI tract
with a Tb of 1 year
Radioactive material enters Liver 1
Part of the material is removed to the GI tract via biliary secretion
The rest goes to blood.
Liver 1
Blood
GI tract
contents
Faeces
On the other hand, data on americium and curium, which may be taken up and/or retained to a lesser extent than plutonium in reticuloendothelial cells, can be reproduced reasonably well if the liver is treated as a uniformly mixed pool that loses activity to blood and the gastrointestinal tract with a biological half-time of 1 year. Material depositing in the liver enters Liver 1, from which part of the material is removed to the gastrointestinal tract contents via biliary secretion, and the rest is removed either to blood (americium) or to Liver 2 (plutonium, neptunium). Material leaving Liver 2 is assigned to blood.

67. Model for Th, Np, Pu, Am and Cm/4
Urine
Uinary
bladder
contents
Kidneys
Other kidney tissue
Urinary path
Blood
Kidneys are assigned two compartments,
One loses activity to urine
Another that returns activity to blood
“Urinary bladder contents” is treated as a separate pool that receives all material destined for urinary excretion
The kidneys are assumed to consist of two compartments, one that loses activity to urine and another that returns activity to blood. The 'urinary bladder contents' is considered as a separate pool that receives all material destined for urinary excretion.

68. Radioactive progeny
A number of radionuclides decay to nuclides that are themselves radioactive
It has been assumed that the decay products would follow the biokinetics of their parents
A few exceptions made for decay products which are isotopes of noble gases or iodine
The revised biokinetic models apply separate systemic biokinetics to the parent and its decay products for intakes of radioisotopes of lead, radium, thorium and uranium.
A number of radionuclides decay to nuclides that are themselves radioactive. The usual assumption in ICRP Publication 30 was that these decay products would follow the biokinetics of their parents, although there were a few exceptions for decay products which are isotopes of noble gases or iodine. In the revised biokinetic models, separate systemic biokinetics have been applied to the parent and its decay products for intakes of radioisotopes of lead, radium, thorium and uranium.

69. Excretion

70. Excretion Urinary bladder and colon are given wT values
Specific information is given on excretion pathways in the urine and faeces in revised biokinetic models for workers.
GI tract model is used to assess doses from systemic activity lost into the faeces.
Secretion of radionuclides from the blood into the upper large intestine is assumed (e.g. for bone-seekers radionuclides)
A urinary bladder model has been adapted for calculating doses to the bladder wall
l = 12 d-1 [ 6 voids / d]
In the biokinetic models described in ICRP Publication 30, no specific information was given on excretion in urine and faeces, although the models were used in Publication 54 for interpreting excretion data. In the Recommendations of the ICRP, however, the urinary bladder and the colon are given explicit wT values, and in the revised biokinetic models for workers given by the ICRP, specific information is given on excretion pathways in the urine and faeces.
For assessing doses from systemic activity lost into the faeces, the model for the gastrointestinal tract is used, assuming secretion of radionuclides from the blood into the upper large intestine. A model for the urinary bladder has been adapted for calculating doses to the bladder wall.

71. References
FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS, INTERNATIONAL ATOMIC ENERGY AGENCY, INTERNATIONAL LABOUR ORGANISATION, OECD NUCLEAR ENERGY AGENCY, PAN AMERICAN HEALTH ORGANIZATION, WORLD HEALTH ORGANIZATION, International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources, Safety Series No. 115, IAEA, Vienna (1996).
INTERNATIONAL ATOMIC ENERGY AGENCY, Occupational Radiation Protection, Safety Guide No. RS-G-1.1, ISBN (1999).
INTERNATIONAL ATOMIC ENERGY AGENCY, Assessment of Occupational Exposure Due to Intakes of Radionuclides, Safety Guide No. RS-G-1.2, ISBN (1999).
INTERNATIONAL ATOMIC ENERGY AGENCY, Indirect Methods for Assessing Intakes of Radionuclides Causing Occupational Exposure, Safety Guide, Safety Reports Series No. 18, ISBN (2002).
INTERNATIONAL ATOMIC ENERGY AGENCY, Intercomparison and Biokinetic Model Validation of Radionuclide Intake Assessment, Results of a Co-ordinated Research Programme, , TECDOC 1071, IAEA, Vienna (1999).
INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Report of the Task Group on Reference Man, ICRP Publication 23, Pergamon Press, Oxford (1975).

72. References
INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Limits for Intakes of Radionuclides by Workers, ICRP Publication 30, Part 1, Annals of the ICRP 2(3/4), Pergamon Press, Oxford (1979).
INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Limits for Intakes of Radionuclides by Workers, ICRP Publication 30, Part 2, Annals of the ICRP 4(3/4), Pergamon Press, Oxford (1980).
INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Limits for Intakes of Radionuclides by Workers, ICRP Publication 30, Part 3 (including addendum to Parts 1 and 2), Annals of the ICRP 6(2/3), Pergamon Press, Oxford (1981).
INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Individual Monitoring for Intakes of Radionuclides by Workers: Design and Interpretation, ICRP Publication 54, Annals of the ICRP 19(1-3), Pergamon Press, Oxford (1988).
INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Age-dependent Doses to Members of the Public from Intake of Radionuclides: Part 1, ICRP Publication 56, Annals of the ICRP, 20(2), Pergamon Press, Oxford (1989).
INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Human Respiratory Tract Model for Radiological Protection, ICRP Publication 66, Annals of the ICRP 24(1-3), Elsevier Science Ltd., Oxford (1994).

73. References
INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Age-dependent Doses to Members of the Public from Intake of Radionuclides: Part 2, Ingestion Dose Coefficients, ICRP Publication 67, Annals of the ICRP 23(3/4), Elsevier Science Ltd., Oxford (1993).
INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Dose Coefficients for Intakes of Radionuclides by Workers, ICRP Publication 68. Annals of the ICRP 24(4), Elsevier Science Ltd., Oxford (1994).
INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Age-dependent Doses to Members of the Public from Intake of Radionuclides: Part 3, Ingestion Dose Coefficients, ICRP Publication 69, Annals of the ICRP 25(1), Elsevier Science Ltd., Oxford (1995).
INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Age-dependent Doses to Members of the Public from Intake of Radionuclides: Part 4, Inhalation Dose Coefficients, ICRP Publication 71, Annals of the ICRP 25(34), Elsevier Science Ltd., Oxford (1995).
INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Age-dependent Doses to Members of the Public from Intake of Radionuclides: Part 5, Compilation of Ingestion and Inhalation Dose Coefficients, ICRP Publication 72, Annals of the ICRP 26 (1), Pergammon Press, Oxford (1996).
INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Individual Monitoring for Internal Exposure of Workers: Replacement of ICRP Publication 54, ICRP Publication 78, Annals of the ICRP 27(3-4), Pergamon Press, Oxford (1997).

74. References
INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Guide for the Practical Application of the ICRP Human Respiratory Tract Model, ICRP Supporting Guidance 3 (in press).
NATIONAL COUNCIL ON RADIATION PROTECTION AND MEASUREMENTS, Deposition, Retention and Dosimetry of Inhaled Radioactive Substances, NCRP Report No.125, NCRP, Bethesda (1997).
NATIONAL COUNCIL ON RADIATION PROTECTION AND MEASUREMENTS, Evaluating the Reliability of Biokinetic and Dosimetric Models and Parameters Used to Assess Individual Doses for Risk Assessment Purposes, NCRP Commentary No.15, NCRP, Bethesda (1998).