|Year : 2019 | Volume
| Issue : 3 | Page : 65-67
Occupational intake of radionuclides series of documents
Hemant Kumar Patni
Internal Dosimetry Section, Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India
|Date of Submission||19-Oct-2019|
|Date of Decision||19-Oct-2019|
|Date of Acceptance||19-Oct-2019|
|Date of Web Publication||06-Nov-2019|
Hemant Kumar Patni
Internal Dosimetry Section, Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Patni HK. Occupational intake of radionuclides series of documents. Radiat Prot Environ 2019;42:65-7
The International Commission of Radiological Protection (ICRP) is planning to publish a series of five part documents on occupational intake of radionuclides (OIR). Three parts of OIR documents are already published as ICRP 130, ICRP 134, and ICRP 137. Remaining two will be published later. These documents will replace the ICRP Publication 30 series,,, and ICRP Publications 54, 68, and 78. These updated OIR documents were required due to the following reasons:
- ICRP updated radiation and tissues weighting factors in the ICRP Publication No. 103. These updated weighting factors were required to be incorporated into computations of internal dose coefficients
- ICRP also updated nuclear decay data in the ICRP Publication No. 107. These decay data need to be incorporated for updating computation of retained fractions/excretion rates and internal dose coefficients
- ICRP published reference computational (voxel-based) phantoms in joint ICRP/ICRU Publication No. 110. They are required for updating the specific absorbed fractions, specific effective energy (SEE), and thereby the internal dose coefficients
- ICRP replaced gastrointestinal tract model with new human alimentary tract model in their Publication No. 100, which needs to be used for updating retained fractions/excretion rates and internal dose coefficients
- Recent studies suggested the need to update human respiratory tract model (HRTM) and systemic models of various radionuclides.
OIR Part 1 (ICRP 130) consists of a revised HRTM. Revision in HRTM was required to match with experimental data of accidental inhalation cases, where long-term lung retentions were much higher than values predicted by the ICRP 66 HRTM model. The revised HRTM contains fractional deposition on various parts of the respiratory tract for aerosol sizes varying from 0.0006 to 20 μm. The default sizes of particles inhaled by the reference worker are assumed to be log-normally distributed with an activity median aerodynamic diameter (AMAD) of 5 μm retained as in the ICRP 66 HRTM. The revised HRTM also contains modifications related to particle transport and absorption to blood. The report also provides an updated target region fractional weight of respiratory tract, colon, and lymphatic nodes for dosimetric considerations. The ICRP 130 also introduces a term called S coefficient (instead of using SEE), thus removing the difference in ICRP and committee on medical internal radiation dose methodology for internal dose coefficient estimation. A new concept of dose per unit content is also defined in this document, which combines dose coefficients with retained fractions/excretion rates. Hence, a measured quantity can be directly converted into committed effective dose (CED) using dose per content. This report uses a term bioassay function for collectively referring to retained fractions or excretion rates. Report also contains details on individual and workplace monitoring programs. For retrospective dose assessment and verification, the report lists two alternative approaches: one using bioassay function to estimate intake from measured quantity and then using dose coefficients to estimate CED and another one where dose per content is used to estimate CED directly from measured quantity. Both approaches can be used in retrospective dose assessment, but the latter approach is less error-prone. This report also emphasizes that if under some circumstances, there is a need to change some parameter values in the computation of effective dose (which refers to dose for a reference person), then instead of changing person-specific data, material-specific data should be changed.
The subsequent reports in this series of ICRP documents contain both bioassay functions and dose coefficients at one place. Unlike ICRP 30 series of documents where most elements had retention–function-based systemic model and physiologically based models for only selected elements, this series has physiologically descriptive model for all elements. The advantages of physiologically descriptive model structure include better extrapolation from animal studies data to human biokinetic model development and better extrapolation from an element biokinetic model to its chemical analogs. OIR Part 2 is published as ICRP Publication 134 which provides the above data for 14 individual elements – hydrogen (H), carbon (C), phosphorus (P), sulfur (S), calcium (Ca), iron (Fe), cobalt (Co), zinc (Zn), strontium (Sr), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), and technetium (Tc) – and their radioisotopes. ICRP 137 (OIR Part 3) provides data for the following 14 elements – ruthenium (Ru), antimony (Sb), tellurium (Te), iodine (I), cesium (Cs), barium (Ba), iridium (Ir), lead (Pb), bismuth (Bi), polonium (Po), radon (Rn), radium (Ra), thorium (Th), and uranium (U) – and their radioisotopes. Both of these documents contain a printed report and an electronic annex.
Printed reports contain a list of main radioisotopes, their physical half-lives, and their decay modes. The printed reports also contain reviews of data on inhalation, ingestion, and systemic biokinetics for radionuclides. Texts also contain the parameter values of the reference biokinetic models, information on chemical forms, and monitoring techniques for the radioisotopes most commonly encountered in workplaces. Dosimetric data provided in the printed publications of the OIR series include tables of CED per intake for inhalation and ingestion, tables of CED per content for inhalation, and graphs of retention and excretion data per Bq intake for inhalation. Data are provided for all absorption types and for the most common isotopes of each element due to default particle size at workplace.
The electronic annex that accompanies this series of reports contains CED and committed equivalent dose coefficients per intake, CED per content functions, and reference bioassay functions due to inhalation, ingestion, and injection. Data are presented for almost all radionuclides included in Publication 107 that have half-lives equal to or >10 min and for other selected radionuclides. Data are provided for various physicochemical forms and for aerosols with median sizes ranging from an activity median thermodynamic diameter of 0.001 μm to an AMAD of 20 μm.
In ICRP 134 and 137, it is observed that for most radionuclides, new dose coefficients are slightly lower (within a factor 2) than those published in the Publication 30 series due to the improvement in biokinetic and dosimetric models for inhalation case. For some rare cases (14 C monoxide,14 C dioxide,59 Fe Type F,90 Sr Type S,60 Co Type S,210 Bi Type F,229/230 Th Type S,234/235/238 U Type S,232 Th Type S,214 Pb Type F, and212 Pb Type F) dose coefficients increased due to revision of the biokinetic models and better description of radionuclide retention and distribution in tissues. For ingestion, most of the dose coefficients are slightly lower than the ICRP 30 series values. The dose coefficients for inhalation of radon and progeny are 3 mSv/mJ h m3 (approximately 10 mSv WLM) for mines and the majority of indoor workplaces.
The biokinetic models provided in these reports are much more sophisticated than requiring for radiation protection purposes. Therefore, the ICRP states that the physiologically based biokinetic models provided in these reports can be used for applications other than radiation protection, including in toxicology, pharmacology, and medicine.
OIR Part 4 will have details for lanthanides and actinides, and OIR Part 5 will deal with remaining elements.
The OIR series of documents contain lot of updates related to internal dosimetry. This editorial is written to encourage professionals involved in internal dosimetry to read the OIR documents before they are adopted by national regulators and get well versed with all the new concepts, models and parameters. A few examples for comparison of the revisions are listed below.
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