Comments for Effective Dose Document (Jaiki Lee)
O This particular document is for clarifying usage of the quantity effective dose(ED). Hence it is good enough to directly get into the problems associated with ED with no need of explaining other quantities(D, DT, HT).
O Unfortunately, previous Publications have not provided clear descriptions on meaning(definition) of ED itself or even carry faulty explanations. This draft document dedicated to ED also follow the track. The followings are my brief summary on ED for your consideration in revision of the document.
In early days of radiation dosimetry until mid-1960s it was only feasible to quantify dose to a small tissue volume suspended in air and radiological control was done based on this quantity. It was assumed that this dose is a conservative estimate of the whole-body dose. The primary dosimetric quantity was the absorbed dose. Available data on relative biological effectiveness(RBE) of different types of radiation and of conditions of irradiation were incorporated in the quality factors introduced in Publication 4(ICRP, 1964) in corporation with ICRU. The quality factor Q was used as a weighting factor to the absorbed dose to define a new quantity ‘dose equivalent’ supporting additivity of doses across different qualities of radiation.
By virtue of advances in digital computers and Monte Carlo radiation transport techniques, it became possible in late 1960s to develop computational models of human body(MIRD-type phantoms) and get detailed distribution of dose inside the body from both external and internal exposures. It was evidenced that, even in case of a whole-body exposure in a broad and homogeneous field of penetrating radiation, absorbed doses or equivalent doses to the organs/tissues differ. In parallel, our knowledge on health effects of radiation exposure accumulated rapidly largely via the follow-up studies of the Japanese atomic bomb survivors to give organ/tissue specific risk of stochastic effects.
This achievement was reflected in Commission’s 1977 Recommendations(Publication 26) where a new approach taking into account the variation of organ/tissue dose equivalents and associated risks in control of exposure was attempted. The new concept was that the total of individual organ/tissue risks should be lower than the acceptable risk to a person as a whole:
where T denotes organs/tissues carrying significant risk of stochastic effects, HT is the dose equivalent to T and Hwb,L is the dose equivalent limit to whole-body. Factor w’s were named just ‘weighting factor’ without explanations of their meaning. However since the equation compares risk, w’s should be risk coefficients per unit dose equivalent. Then Commission’s 1978 Stockholm statement caused some conceptual gap by naming the weighted sum of dose equivalent ‘effective dose equivalent’. The summed quantity cannot be a dose because doses to different organs/tissues are not additive conceptually.
The 1990 Recommendations(Publication 60) took somewhat different approaches: firstly, the radiation weighting factor, wR, was introduced to be used instead of the quality factor Q in definition of a dose quantity additive across different qualities of radiation. The latter quantity was named ‘equivalent dose’ which was conceptually corresponding to the dose equivalent but not measurable. Secondly, ‘weighted sum’ of equivalent doses was named ‘effective dose’ and the weighting factors, named ‘tissue weighting factors’, were driven from rounded value of relative contribution of each organ/tissue to total health detriment. Thirdly, the effective dose limits were set by comparing the resulting risk due to a given annual whole-body uniform dose with the annual risk judged to be unacceptable to exceeded. With these changes, it became clear that the effective dose is defined to be the detriment-weighted-mean equivalent dose over the whole-body of the reference person. Here the detriment relates to the stochastic health effects at low dose delivered at low dose rate. Hence the equation is mathematically ‘sum’ but should be interpreted as ‘weighted-averaging’ because doses to different tissues cannot be summed. The averaging does not cover all the organs/tissues in the body but it can be interpreted that these organs/tissues have trivial or negligible values of tissue weighting factor relating stochastic risk so as not to affect the averaging.
Then the effective dose meets the necessity that a single dosimetric quantity appropriately presenting health risk of exposed person, even rough but risk-informed, might be useful for pragmatic radiological protection practices. The concept ‘averaging over whole-body’ is in line with the assumption ‘uniform exposure of the whole-body’ in evaluation of health detriments to set the effective dose limits.
In the 2007 Recommendations, adjustments of the radiation weighting factors and tissue weighting factors were made, new reference phantom models were introduced together with clarification of the procedure to get the sex-averaged equivalent doses. But the conceptual frame of protection quantities remained unchanged.
O Giving up use of equivalent dose in setting limits to prevent tissue reactions, together with the current ICRU position attempting to redefine the operational quantity, can be a major change in the system of radiological protection. We have to keep in mind that additivity of doses across types of radiation is supported by those weighted quantities like dose equivalent, equivalent dose or RBE weighted absorbed dose. Hence this level of change should be introduced via amendment of the basic Recommendations, not by a supplement document. It requires a common approach between ICRP and ICRU. So it is better at this time to focus just on the use of ED in this document. Instead, ICRP should set up ASAP a task group for making revision of the Recommendations. It should be noted that the current Recommendations carry serious conceptual problems in categorizing exposure situations and exposure types(a few appear below).
Page | Line | As is | Should read |
5 |
| (abstract) | May be modified when the main text is fixed. |
8 | 185-198 | 1st thee bullet points | May be deleted to focus on ED. Mind there are some erroneous explanations. |
8 | 199 | Effective dose is calculated as the weighted average of organ/tissue equivalent doses, summing equivalent doses multiplied by tissue weighting factors (wT) which provide a simplified representation of fractional contributions to total stochastic detriment from cancer and hereditary effects. Detriment-adjusted nominal risk coefficients (Sv-1) are calculated | Effective dose is the equivalent dose to the body as a whole, which is defined as an indicator for the total stochastic detriment from cancer and hereditary effects. Hence the effective dose is calculated as the detriment weighted average of organ/tissue equivalent doses over the whole body. Weighting is done by the tissue weighting factors of which values assigned on the basis of detriment-adjusted nominal risk coefficients. The detriment-adjusted nominal risk coefficients (Sv-1) are calculated |
8 | 207 | risk-adjusted measure of total body dose | risk-adjusted measure of exposure of a person |
8 | 216 | ages | age groups |
8 | 217 | definition of E includes the specification | definition of E includes use of reference phantoms. Detailed specification of reference adult male and female phantoms for radiation transport calculations is given in Publication 110(ICRP, 2009). |
8 | 222 | in emergency exposure situations at acute doses in the range | at acute higher doses in the range
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9 | 225 | specific | particular |
9 | 239 | from internal exposures during | from intake of radionuclides during |
9 | 242 | (amend the para) | However, the Commission will review appropriateness of extending these period taking into account the increasing mean lifetime. |
9 | 250 | the use of constraints and reference levels | the use of dose limits, constraints and reference levels |
9 | 252 | pragmatic, equitable and workable system | pragmatic and workable system |
9 | 265 | of unintended exposures or overexposures of patients. | of accidental exposures of patients. |
9 | 268 | possible risk | risk |
11 | 293 | introduced in the 1977 Recommendations | Please provide the history correctly. The 1977 Recommendations(Pub. 26) only introduced to apply the dose equivalent limits when HT’s are significantly inhomogeneous over the whole-body(here HT is dose equivalent to tissue T). No name was given for the sum quantity. In the 1978 Stockholm statement of the Commission, it is named ‘effective dose equivalent’ with notation HE. In 1990 Recommendations, ‘radiation weighting factor’ and ‘equivalent dose’ were introduced to take the roles of the quality factor and the dose equivalent, respectively. The quantity corresponding to the effective dose equivalent is named effective dose. Unfortunately, the needs of E and its meaning have not explained explicitly in these courses. It is better to provide in this document the brief reason of introducing ED.
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11 | 304 | from external sources to provide | from external sources emitting radiation of different types to provide |
11 | 306 | potential stochastic effects of whole-body radiation exposure | risk of stochastic effects in the whole body |
11 | 313 | of effectiveness of radiations | of effectiveness of certain types of radiation |
11 | 315 | The final step is to sum the equivalent doses to individual organs and tissues, multiplying each by a tissue weighting factor that represents its contribution to total detriment from uniform whole-body irradiation. | Doses to different tissues cannot be summed, conceptually. If we consider the tissue weighting factors as risk conversion factors, then becomes the risk to the tissue and this quantity can be summed to get total risk. But in this case, the quantity is not a ‘dose’ having unit of ‘J/kg’ anymore and we cannot call it ‘effective dose’. The final step is to evaluate the detriment weighted average equivalent dose over all the organs and tissues of interest from the view point of radiological protection by applying normalized weighting factors named tissue weighting factors, to present the exposure with a detriment informed single quantity for pragmatic uses in radiological protection. |
11 | 318 | effective dose is a weighted average of organ/tissue doses | effective dose is a detriment-weighted mean equivalent dose to the whole body |
11 | 318 | The intention is that the overall risk should be comparable irrespective of the type and distribution of radiation exposure; E, expressed in Sv, is the well-known quantity that is often referred to simply as “dose”. | The intention is that the doses should be comparable irrespective of the type and distribution of radiation exposure. When the term "dose" with no qualifier is used to present degree of exposure of persons, it often refers to the effective dose. |
11 | 326 | values of effective dose for | values of equivalent dose for |
11 | 327 | low doses (< 100 mGy low-LET radiation) | Often being asked what the time frame is for this expression. Could we clarify it? |
12 | 341 | ICRP | Most of the acronym ICRP appears in the draft should be ‘the Commission’. |
19 | 644 | as the sum of equivalent doses to individual organs and tissues multiplied by their tissue weighting factors, thus making allowance for their contribution to total detriment. Effective dose is a weighted average of equivalent doses to organs and tissues, used as a measure of whole-body dose.
| as a weighted mean equivalent dose over the whole-body. Tissue weighting factors are the normalized weighting factors used in the weighted averaging. Thus the effective dose is a hypothetical equivalent dose to the whole-body. |
19 | 662 |
| May show the total as |
20 | 669 | consider | present |
23 | Table 2.5 | (cases power 100 per Gy) from uniform external exposure | (cases per 100 per Gy) from external exposure
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25 | 830 | fndamental | fundamental |
25 | 834 | Values of the equivalent dose to organs and tissues are weighted using tissue weighting factors that provide a simplified representation of relative detriment and the weighted equivalent doses are then summed to give the effective dose. This quantity is used to sum exposures to radiation from incorporated radionuclides and to external radiation fields. The description below is | The equivalent doses to organs and tissues are averaged over the whole body by weighting corresponding tissue weighting factors to get the effective dose. The description below is |
25 | 839 | Publication 103 (ICRP, 2007a). | Publication 103 (ICRP, 2007a) but some modifications applied. |
25 | 841 | In radiation biology, clinical radiology, and radiological protection, the absorbed | The absorbed |
25 | 843 | any irradiation geometry | any material being exposed |
25 | 859 | of the skeleton. | of the skeleton to get the mean absorbed dose to tissue or organ T, DT. |
26 | 861 | The definition of the protection quantity, equivalent dose, is based on the average absorbed dose (DT,R) due to radiations of type R in the volume of a specified organ or tissue T. The radiation types R are given by the type and energy of radiation either incident on the body or emitted by radionuclides residing within it. | (strike out) It is known biophysically that high LET radiation is more effective to induce damages in biological molecules than low LET radiation. |
26 | 864 | The protection quantity equivalent dose in an organ or tissue (HT) is then defined by
where wR is the radiation weighting factor for radiation type R. The sum is performed over all types of radiations involved. | the differences in biological effectiveness of different types of radiation, and defined by weighting the mean absorbed dose, , by a factor derived from the relative biological effectiveness(RBE) of the type of radiation irradiated. This factor is named radiation weighting factor, wR, and their values are assigned by the Commission. Then the equivalent dose is determined by . |
26 | 869 | sievert(Sv). | sievert(Sv). wR applies for the radiation type entering the body tissues. |
26 | 884 | radiation incident on the body or, for internal radiation sources, emitted from the source. | radiation entering the body tissue. (note: in case of microball containing radionuclides it is not clear what the radiation emitted from the source is.) |
28 | 931 | consideration is the relationship between effective dose and measurements made using operational quantities | (It should be noted that need of the operational quantity concept is under review by ICRU). |
28 | 946 |
| (We may delete whole sections 3.2 and 3.3 and just focus on the effective dose.) |
28 | 949 | is defined as: where wT is the tissue weighting factor for tissue, T and . | is given by: where wT is the tissue weighting factor for tissue, T and . However, the sum over R causes confusion. Since the reason for defining the equivalent dose is to support additivity of doses due to different types of radiation, both equivalent doses and effective doses should be additive across different types of radiation. For absorbed doses, their additivity does not hold for different qualities of radiation. For the purpose of defining the equivalent dose, the Commission allowed addition of mean absorbed doses from different types of the secondary radiation generated inside the body due to a primary radiation entering body tissues. A typical example is neutron exposure: neutrons entered the body may generate heavy charged particles, photons or electrons and these particles should produce absorbed doses to a certain volume of interest separately. These absorbed doses should be summed to apply the radiation weighting factor, which means the equation for E should read:
where r denotes types of the secondary radiation due to the primary radiation R. (Alternatively, we may define the mean absorbed dose to tissue T due to a primary radiation R entering body tissue, DT,R, as the sum of mean absorbed doses to tissue T produced by every types of secondary radiation. Then we may write and . Even, we may modify the definition of mean absorbed dose, DT, to include all the contributions of secondary radiation to get and if it does not cause conflict to the definition of absorbed dose prescribed by ICRU.) |
28 | 951 | The sum is performed over all organs and tissues of the human body for which specific radiation detriment values can be calculated (Table 2.1) and tissue weighting factors can be specified (Table 2.3). | The averaging is performed over the whole human body. (Other tissues for which no values of tissue weighting factor are assigned, are considered having trivial weights) |
28 | 955 | are chosen to represent the contributions of individual organs and tissues to overall radiation detriment from stochastic effects | are chosen to represent simplified and normalized relative detriment from stochastic effects |
28 | 957 | The wT values are rounded and have only four different numerical values (Table 2.3), despite the greater differentiation | The Commission assigns only four different numerical values (Table 2.3) rounded, despite the further differentiation |
29 | 970 | considered and avoided.
| considered.
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29 | 985 | by workers and members of the public | by workers and general population |
30 | 1019 | (Cristy, 1980; | (Fisher and Snyder, 1967; Cristy, 1980; Fisher and Snyder are the pioneers in developing anthropomorphic phantoms. Fisher H. L. J. and Snyder W. S(1967). Distribution of Dose in the Body from a Source of Gamma Rays Distributed Uniformly in an Organ, ORNL-4168, Oak Ridge National Laboratory. |
30 | 1040 | The radiations considered are external beams of monoenergetic photons | The types of radiation considered are monoenergetic photons |
30 | 1043 | ICRP/ICRU recommended values | ICRP/ICRU reference values |
32 | 1128 | operational dose equivalent quantities | operational quantities
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32 | 1131 | taken as a sufficiently 1131 precise assessment of | taken as reasonable estimates |
32 | 1133 | for occupational exposures | for exposures |
32 | 1138 | d = 10 mm and Hp(10) | d = 10 mm or Hp(10) |
32 | 1140 | an effective dose value that is sufficiently precise for protection purposes. | a reasonable estimate of effective dose. |
33 | 1145 | importance of the lens of the eye | importance of eye protection |
33 | 1161 | the operational quantities are | the monitoring quantities are (In this case, it is questionable to call it operational quantity.) |
33 | 1180 | given by: | given as the detriment-weighted mean of committed equivalent doses over the whole body: |
34 | 1217 | account of the group of persons exposed to radiation and the period of exposure. | account of a particular group of persons due to a given source
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34 | 1218 | The specified quantities have been defined as the collective equivalent dose (ST) which relates to a tissue or an organ T, and the collective effective dose (S) (ICRP, 1991b, 2007a). | (stike out) |
35 | 1253 | occupational exposure situation. | occupational exposure. |
35 | 1258 | is a useful tool for operational radiation protection, notably when planning complex work involving multiple workers where it is important to consider collective exposures as well the exposure to the individual workers. | is, together with the distribution of individual doses, an important factor to be considered in optimisation of protection. |
35 | 1264 | the potential increase | the protection cost and the potential increase |
35 | 1271 | However, it is important to note that although effective dose is estimated for a specific individual, it remains a formal protective quantity in the system of radiological protection. | (intention under this is not clear) |
36 | 1291/1293 | sufficiently precise | reasonable |
36 | 1312 | concentrations in air or other media such as surface contamination. | concentrations in air. |
37 | 1341 | potential exposures | consequence of an accident
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37 | 1345 | radionuclides in the workplace and from man-made radionuclides | radionuclides and from wide-spread man-made radionuclides |
37 | 1347 | resulting from an emergency situation | resulting from an accident |
37 | 1348 | The treatment of occupational exposures due to radon isotopes, primarily radon-222, and their decay products is addressed in Publication 126 (ICRP, 2014). | (I have a strong objection to saying that occupational exposure to radon belongs to an existing exposure situation. Whatever the source is in normal situation, doses to worker should be below the dose limits as long as the exposure is not excluded or exempted. Applying the dose limits means that the situation is planned one.) |
37 | 1357 | Firstly, if there is an accident or failure in control in the workplace, workers may be exposed to higher than normal radiation exposures. It is important to quickly assess what such exposures might have been in order to determine if medical intervention is required. | (Wrong concept. Serious exposure accident already happened is not an emergency exposure situation but simply an accident. Prevention or reduction of risk of potential exposure and treatment of accident victims should be separately dealt from exposure situations.) |
38 | 1379 | Paragraph (78) | (This is also a topic of victim treatment, not an issue of emergency exposure situation). |
38 | 1410 | small to be detected. | small to be detected . Therefore, doses are estimated with release source term and environmental pathway models in most cases.
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38 | 1415 | or radiological emergencies | or radiological accidents |
38 | 1416 | from past activities that were subject to regulatory control but not in accordance with current requirements, | from legacies of past activities |
39 | 1419 | that incorporate natural or residual man-made radioactive material | that incorporate natural or residual man-made radionuclides but are not excluded or exempted |
39 | 1428 | operation of a planned exposure situation, | emergency operation at a source, |
39 | 1432 | dispersed in natural or inhabited environments | dispersed in the environment |
40 | 1471 | The full set of six age-groups are the 3 month-old infants, 1 year, 5 years, 10 years, and 15 years old children and adults. | (Now we provide for only 3 age groups) |
40 | 1497 | allow for the contribution of individual organs and tissues to total stochastic detriment while not over-interpreting knowledge of risks of low dose radiation exposure. | allow for averaging the equivalent doses over whole body to roughly present the total detriment with a single quantity.
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41 | 1528 | and for emergencies. | and for accident conditions. |
41 | 1540 | Collective effective dose can be used | Individual dose distribution comprising the collective dose can be used |
41 | 1544 | process for planned, existing or emergency exposure situations.
| process for allexposure situations.
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45 | 1670 | 1) that use of radiation in medicine should do more good than harm, 2) that a given type of procedure is justified for a particular clinical indication as it will improve the diagnosis or treatment of patients; and 3) that a medical examination for an individual patient will do more good than harm, by
| 1)that the proper use of radiation in medicine is accepted as doing more good than harm to society, 2) that a specified procedure with a specified objective is defined and justified, 3) that the application of the procedure to an individual patient should be justified, by |
45 | 1678 | different kinds of examinations | different kinds of procedures |
45 | 1688/1690 | examination/examinations | procedure/procedures |
45 | 1690 | x-ray | external |
45 | 1696 | Patient imaging procedures
| Medical procedures (Generalize beyond imaging) |
45 | 1699 | with different imaging modalities, even when a similar region of the body is being imaged. | with different modalities, even when a similar region of the body is being irradiated. |
45 | 1700 | from machine-produced x-ray and | from external beam and |
45 | 1701 | for use in straightforward comparisons | for use in handy comparisons |
46 | 1716 | regarding an imaging procedure | regarding a medical procedure |
46 | 1721 | radiation dose to a minimum or to | radiation dose to |
46 | 1724 | Modality-specific dose | Modality-specific and directly measurable dose |
46 | 1743-1752 |
| (this paragraph should go together with para. 110(carer) |
46 | 1753-1771 | Reporting of unintended exposures | (unintended exposures are not medical exposures but exposure accidents. Hence it is better place this paragraph at the end of section 5(Medical exposure), with this caveat.) |
47 | 1786 | Assessments of potential exposures and | Assessments of exposure potential and |
47 | 1791 | risk to individuals, it is considered reasonable to use effective dose to a reference person as | risk to specific individuals, it is considered reasonable to use effective dose as |
48 | 1797 | benefits of medical exposures | benefits of medical achievement (exposure itself is not a benefit) |
48 | 1799 | take these potential risks | take these risks (‘risk’ incorporates potential or probability) |
48 | 1800 | or interventional exposures | or interventional procedures |
48 | 1807 | involving potential radiation exposure of the public | involving exposure of the public |
48 | 1812 | optimisation of examinations | optimisation of examinations |
48 | 1819 | effective dose of 10 to 100 mSv | (Need to clarify the time frame) |
48 | 1832 | an unrealistic fear | an undue fear |
48 | 1833 | effective dose to a reference person can | effective dose can |
48 | 1835 | perspective of possible risks from radiation exposure. The potential risk from | perspective of risks from radiation exposure. The risk from |
49 | 1842 | Table 5.2 | (May add another entry 1000s named ‘high’ to cover therapy level and state ‘Effective dose is less useful’.) |
49 | 1853 | Depending on the risk projection models used, there are also differences between populations. | There are also differences between populations. |
50 | 1877 | Fig. 5.1 presents | Figure 5.1 presents |
54 | 1968 | to penetrating low LET radiations. | to low LET radiations. |
54 | 1982 | (para 123) | (Note that ICRU also attempts direct relation of kerma and effective dose without help of concept of operational quantity.) |
55 | 2016 | fetus is regarded as a member of the public for the purposes of dose limitation (ICRP, 2007a). | (I agree with this expression. But I doubt if there is such expression in Pub. 103.) |
56 | 2049 | “critical group” and is an estimate of effective dose to a hypothetical person of specified age receiving a dose that is representative | “critical group” and is representative |
57 | 2091 | consideration of protection options for accidental exposures of workers and members of the public. | consideration of treatment of victims of an accident. (Victims are simply victims, no meaning of classification such as worker, public or patient) |
57 | 2098 | Collective effective dose can be | Collective effective dose, together with distribution of individual doses, can be |
`57 | 2102 | They also have a useful role in comparative studies to consider the effects of adopting different systems of treatment for radioactive wastes or the radiological impact of different sources of exposure. | (Isnt this conflict to the statement that the collective dose may have little meaning for small doses assumed to be in the far future? Geographic information is not good enough to give meaning to the estimated collective dose.) |
57 | 2105 | for the prediction | for the meaningful prediction |
57 | 2107 | of extremely low (μSv or nSv) levels | of extremely low (μSv) levels |
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