The American Association of Physicists in Medicine (AAPM) is pleased to submit comments to the International Commission on Radiological Protection (ICRP) on its draft document entitled, “The Use of Effective Dose as a Radiological Protection Quantity.” The AAPM commends ICRP for working to address the need for guidance and clarification for use of the quantity ‘effective dose’ relating to medical exposures.
The AAPM, however, is concerned that the draft report does not provide the needed clarity on how effective dose should, and should not, be used, particularly in the context of medical exposures. The AAPM believes this draft report provides an opportunity to frame radiation risks and benefits in medical exposures in a more logical and balanced way. Accordingly, the AAPM urges the ICRP to focus its attention on the reasonable evaluation of benefit as well as risk, rather than on evaluation of radiogenic risk alone.
Effective dose is internationally accepted and applied as a central radiation protection quantity in a system for radiological protection. The AAPM believes effective dose is thus an important tool for administratively accounting for and controlling the dose from internally deposited radionuclides and external radiation exposure from various sources. We believe, however, that risks associated with medical procedures are best evaluated using appropriate risk values for the individual exposed tissues and for the age and sex distribution of the individuals undergoing the medical procedures. Moreover, AAPM asserts that effective dose should not be used as a quantitative predictor of any stochastic risks from radiation exposure.
We have submitted our specific comments and recommendations. The AAPM hopes that the ICRP will consider AAPM’s comments in the accompanying table and adopt AAPM’S recommendations when crafting the final document.
General
Effective dose is internationally accepted and applied as a central radiation protection quantity in a system for radiological protection. Effective dose is an important tool, attempting to solve the conceptual and practical problem of administratively accounting for and controlling the dose from internally deposited radionuclides and external radiation exposure from various scenarios.
However, as discussed in numerous publications of the United Nations Scientific Committee on the Effects of Atomic Radiation, ICRP, and NCRP, risks associated with medical procedures are best evaluated using appropriate risk values for the individual tissues exposed and for the age and sex distribution of the individuals undergoing the medical procedures. Further, ICRP has repeatedly emphasized that effective dose was not intended, nor should it be, as a quantitative predictor of any stochastic risks from radiation exposure. This is especially true for predicting cancer incidence or mortality from diagnostic imaging procedures where the effective doses are small (<10 mSv) and the population exposed is large! Nevertheless, it has often, inappropriately, been used in medical literature as a surrogate for whole-body dose or “risks” from diagnostic x-ray procedures. In its most egregious form, this dose is used to calculate estimates of cancer incidence and mortality in large populations of past or future patients.
The American Association of Physicist in Medicine (AAPM) is concerned that the draft report does not provide the needed clarity on how Effective Dose should, and should not, be used, particularly in the context of medical exposures, where the benefit side of the risk/benefit ratio is not accounted for in the current formulism for Effective Dose. It is our hope that these issues can be addressed clearly and specifically in the final report.
The AAPM has issued AAPM Policy PP-25-B that specifically addresses some of the important issues associated with the concepts of the draft ICRP document, stating the following “The American Association of Physicists in Medicine (AAPM) supports the position that medical imaging should be appropriate and should use the radiation dose necessary to accomplish the clinical task. At the present time, epidemiological evidence supporting increased cancer incidence or mortality from radiation doses below 100 mSv is inconclusive. As diagnostic imaging doses are typically much lower than 100 mSv, when such exposures are medically appropriate, the anticipated benefits to the patient are highly likely to outweigh any small potential risks. Given the lack of scientific consensus about potential risks from low doses of radiation, predictions of hypothetical cancer incidence and mortality from the use of diagnostic imaging are highly speculative. The AAPM, and other radiation protection organizations, specifically discourages these predictions of hypothetical harm. Such predictions can lead to sensationalistic stories in the public media. This may lead some patients to fear or refuse safe and appropriate medical imaging, to the detriment of the patient. Medical physicists continuously strive to improve medical imaging by optimizing radiation doses while ensuring that the needed level of image quality is obtained, thereby contributing to the widely recognized benefits of medical imaging.”
It is our hope that the final version of this report provides clear statements on these matters and that such statements are in general agreement with AAPM Policy PP-25-B, which received considerable review and revision throughout our organization prior to its adoption. Specifically, we request that the ICRP clearly denounce the use of Effective Dose as a surrogate of risk for doses below 100 mSv, and that the use of Effective Dose to estimate future cancers or cancer deaths be similarly denounced.
The TG-89 Draft on the use of effective dose as a radiological protection quantity inappropriately promotes the use of effective dose as a radiation-risk quantity or indicator.This ICRP publication will therefore effectively propagate and in fact encourage the inappropriate use of effective dose as a metric of individual risk. It is strongly recommended that this document state explicitly that effective dose is inappropriate for risk projections and should not be used for this purpose. Otherwise, it may lead to more, not less, confusion regarding the appropriate use of effective dose, especially when considering language used in the report such as “unintended use” vs. “reasonable estimate” or “appropriate caution” (which is not specified), or “uncertainty” (which is not quantified nor are ranges provided).
The document is rather confusing on the topic of appropriate use of Effective Dose. Effective dose is a radiation protection quantity and much of the document supports that use (and states that other “unintended” uses would be inappropriate). Yet the use of effective dose as an approximate indicator of risk is not clearly presented or supported in this document. In fact, with all of the caveats needed in explaining its potential use as an indicator of risk, one is left wondering if it is even appropriate at all.
This document provides an opportunity to frame radiation risks and benefits in medical imaging in a more logical and more balanced way. Risk-focused analyses (to the exclusion of comparable consideration of benefit) have led to unwarranted concern in many instances about undergoing needed medical examinations that involve ionizing radiation. Thus, the focus on the use of radiation in medicine should not be on radiogenic risk exclusively (as is now typically the case) but on reasonable evaluation of benefit as well as risk. The current ICRP document misses an opportunity to do so.
The number of significant figures used to express effective doses should be limited. For example, expressing effective doses to three significant figures, or a precision of 1 in 1,000, is unjustified.
In several areas of this document, rather than copy and paste the definitions of relevant quantities directly from ICRP Publication 103, the document inappropriately summarizes or edits these definitions in such a way as to appear to change the original intended definitions. It is imperative that the original definitions and equations be utilized. Alternatively, specific justifications for any changes in definitions must be provided.
Paragraph 6 of the document lists “…identified issues including the following…” and paragraph 7 notes “The following section…address the issues enumerated above.” However, each of the issues listed is not addressed in the document, and it is very difficult to follow along the flow of the document to find discussions or recommendations related to the issues. An overall clarification and revised flow of the document is suggested.
Line 119-120
By the use of the wording “…may be considered as an approximate indicator of possible risk…”, it appears that ICRP is inappropriately recommending such use or giving permission for such use. Also see 268.
Line 186
Re: “The dosimetric quantities,” certainly, other quantities are used as well. “The” suggests that these are all there are.
Gray is not the special name for absorbed dose as indicated; rather gray is the special name for the unit of absorbed dose.
Line 187
Similarly, sievert is not the special name for equivalent dose or effective dose; rather sievert is the special name for the unit for each of these quantities.
The SI units are indeed the gray and sievert; it is incorrect to imply otherwise as the sentence does. The BIPM terms gray and sievert “SI derived units,” which are combinations of base units of the SI.
Line 186-187
In light of three previous comments, please consider changing sentence to read something like “The fundamental dosimetric quantities used in radiological protection are absorbed dose (D), with the unit given by the special name of gray (Gy), and equivalent dose (H) and effective dose (E), both with the unit given by the special name of sievert (Sv); both Gy and Sv are derived units in the International System of Units (SI) equal to 1 J kg-1.” Further refinement of this statement is suggested below in comment to line 1942.
Line 196-198
This section encapsulates a very important point, however the title of the document is about “The Use of Effective Dose…” and this point about not using equivalent dose to set limits on organ/tissue doses would not seem to fit. Should the title be expanded?
Line 212 (and several other sections)
The phrase “E requires the assumption…” is not technically accurate. E is predicated (or based on) such an assumption. It doesn’t ‘require’ such an assumption.
Line 221
Why “generally be used at doses below 100 mSv”? There are therapeutic medical exposure scenarios where patients receive a cumulative E of say 100-200 mSv? Would consider rephrasing to something like “Although E will most commonly be used at doses below 100 mSv”.
Line 267
For optimization of medical patient dose, short-term effects are an important consideration and E does not take them into account.
Line 267-270
It should be emphasized that the uncertainties associated with risk projection for low doses or dose rates have been estimated by UNSCEAR, ICRP, NCRP, and others to be at least factors of 3 or more in both directions, even before variations of risk with age (perhaps another factor of 2 or more), sex, and population group, let alone individual genetic factors. Therefore, it would seem rather inappropriate to utilize effective dose as an “approximate indicator of risk”. The uncertainties are much too large to make such a claim.
Line 254-270
Any derivation of or indication of risk estimates based on the effective dose construct are only somewhat related to overall stochastic risks from the exposure to ionizing radiation and do not in any way attempt to account for other pertinent benefits/risks that could be influenced by the use of radiological imaging in medicine. The suggestion of quantification of stochastic radiation-induced risks in medical imaging is often times presented in the absence of any other quantitative information related to the risks or benefits involved in medical decision-making, which seems to have an understated importance in the larger public perception of radiation-induced risks.
Line 275
Should refer to patient populations with limited life expectancy, as well as diseases with intermediate prognoses.
Line 293
The given history of effective dose concept and construct is not consistent with ICRP’s previous documents.
Line 299-300
“…which include its interpretation as a measure of risk to individual patients, contrary to its intended use…”. The introduction by ICRP in this document to allow effective dose as an “approximate indicator of risk” would certainly result in many more folks interpreting as a measure of risk to individual patients, exactly contrary to the original and appropriate use of effective dose as a radiation protection conceptual construct.
Line 321
“It is important to recognize that while E is a risk-related construct for use in radiation protection…” Did ICRP Publication 103 describe E as a risk-related construct?
Line 328
“…associated risks…are uncertain…” The large range of uncertainties should be described in this document, as supported by UNSCEAR, ICRP, and NCRP analyses that have shown minimum ranges of about plus or minus 300% about any nominal estimates. Such large uncertainties are the very reasons that in Publication 103, ICRP does NOT intend effective dose as a risk indicator.
Line 333
Clarify …is dependent on cancer type and this difference may be larger for liver cancer than for leukemia.
Line 363
“However, further clarification and guidance have been sought…” This document does not address, further clarify, or provide guidance in each of the areas noted in the list.
Line 374-375
How is “dose equivalent” a measured quantity, is this referring to operational quantities?
Line 411-417
Citing ICRP 103, distinction is made here between “Tissue reactions (Deterministic effects)” and “Cancers and heritable diseases (Stochastic effects)”. In ICRP 103, the primary terms used are Tissue Reactions and Stochastic Effects. Accordingly, for consistency, consider reversing “Cancers and heritable diseases (Stochastic effects)” to read “Stochastic effects (Cancers and heritable diseases)” so that the primary terminology is in both cases not in parentheses.
Line 428
“…indicated a lower threshold for induction of cataracts…” ICRP Publication 118 shows that the nominal threshold was for opacifications (that might/could lead to cataracts) as there was still not enough information on mechanisms of cataract progression.
Line 466
This section on CVD thresholds appears to draw upon only the literature put together prior to ICRP Publication 118, several more recent reviews have been performed that should be included. See for example NCRP Commentary No. 27.
Line 470
“…the current view is that different mechanisms of damage are likely to predominate at high and low doses…” is this statement saying that such a dichotomy of mechanistic responses is correct, in the view of ICRP, or thatit has been widely demonstrated in the literature?
Line 474
See comment to 411-417 and consider reversing order and parentheses here as well.
Line 494
“Epidemiology provides limited evidence of DDREF for solid cancer in humans…” It should rather be argued that both the Ruhm and Shore papers referenced provide evidence of DDREF from across several studies. Also see Hoel 2018 https//www.ncbi.nlm.nih.gov/pubmed/29400635.
Line 502
For completeness, the addition of the recently published NCRP Commentary No. 27 “Implications of Recent Epidemiologic Studies for the Linear-Nonthreshol and Radiation Protection” should be considered.
Line 505
How is it that the NT dose-response assumption allows for “…the addition of external and internal doses…” ??
Line 516
Why is section 2.4 included at all in this document, the presentation is mostly (but not always) from previous ICRP documents that should simply be referenced (or copied explicitly).
Line 521
The statement “These risk coefficients are not intended for use in estimating risks to specific individuals” is exceedingly important and is part of the reason this document is rather confusing.
Line 552
Was the “…available cancer survival data…” also population and sex averaged?
Line 561
Are the values in Table 2.1 different that previous values utilized by ICRP when setting Publication 103 guidelines? Has new data become available in the last 10 y that would change any of the foundational assumptions?
Line 726
“Particularly in medical applications but also in other applications, there are situations in which there is a requirement for some understanding of risks associated with particular procedures and better information may be required than that conveyed by nominal risk coefficients.” This is the very reason that we should be extremely cautious about suggesting that a nominally determined effective dose construct (which is several steps further down the uncertainty pathway) can be an “approximate indicator of risk” for medical applications (and presumably the unnamed other applications as well).
Line 730
“Genetic” can also indicate heritable effects. This seems to refer to the expression of genes, so this section can benefit from being more specific.
Line 732
This sentence needs clarification “There are good prospects…”.
Line 737
Table 2.4 – at a minimum the title should include “nominal” as well as specific footnote to include a description of the plethora of assumptions made in developing the values.
Line 755
Table 2.5 - at a minimum the title should include “nominal” as well as specific footnote to include a description of the plethora of assumptions made in developing the values.
Line 827
Dosimetry section. Many of these descriptions, equation parameter descriptions, and texts differ from ICRP Publication 103. As an example, paragraph (33) is NOT consistent with ICRP Publication 103 paragraph (106). Much care should be taken not to editorialize or change previous definitions or descriptions of these fundamental quantities. Any imprecision in wording will surely cause significant confusion.
Line 857
This document uses “…is carried out over the volume of a specified organ…” while ICRP Publication 103 (paragraph 110) uses “…mass…” Such inconsistencies in definition are inappropriate, ICRP Publication 103 or ICRU definitions should be held to very specifically.
Line 876-877
The section on RBE needs much work. RBE is the ratio of dose of the low-ET reference radiation to the dose of higher-ET test radiation for the same level of observed effect. ICRP Publication No. 60 defines as “the RBE of one radiation compared with another is the inverse ratio of the absorbed doses producing the same effect.” It is important that it be described as a “ratio of absorbed doses” rather than just “doses”.
Line 937
“…appropriately set in terms of absorbed dose…” should this be in terms of “mean organ/tissue dose”?
Line 948
WTis defined and discussed. Should this section also define and discuss WRand DT,R?
Line 949
The discussion of effective dose here is slightly different than presented in ICRP Publication 103 and a direct excerpt from that document should be used, not an editorialized version.
Line 963
“…and questions have arisen regarding the upper limit…” While the question is noted, the explanation is considered weak, here listed as “In principle there is no reason why effective doses should not be used as a quantity at doses above 100 mSv…”.
Line 976
Clarify this is internal dose.
Line 988
ICRP 128 from 2015 should be included in this list.
Line 1036-1037
Since ICRP is planning on issuing a set of reference phantoms for children of different ages and for pregnant women and fetus, shouldn’t this document be held and updated with those reference models and not just for adults as given in the tables?
Line 1077-1081
Similarly, since ICRP (and ICRU) are still working on significant changes to operational quantities as well as updated dose coefficients, should this document reflect those updates?
Line 1127
Operational quantities section – again, as significant changes are proposed for operational quantities and definitions, it would seem that this document should await those changes.
Line 1197-1213
Paragraph (64) – this whole section is extremely limited in scope and detail. Much of the available and most recent literature is not included. Also “calculated” should be “estimated”.
Line 1206
There are many more such publications and a review of the current literature is needed to be included in this section, otherwise ICRP appears to be acknowledging only these approaches.
Line 1230-1232
“…the computation of cancer deaths based on collective effective doses involving trivial exposures to large populations is not reasonable and should be avoided…” is exceedingly important, as this inappropriate use of effective dose can be found, not uncommonly, in the medical literature and on various web sites. This statement, therefore, warrants a more prominent place in the publication, for example, in the Abstract. Also, consider utilizing one of the proposed terms for dose level from Table 5.2, such as “low levels and below” rather than an undefined “trivial”.
Line 1304
“Clinicians performing interventional procedures would wear two dosimeters…” Is this a specific, generalizable statement? Are all IR docs wearing 2 dosimeters in this manner? What does current ICRP guidance recommend?
Line 1329
Urinalysis is but only one potential method of doing a bioassay. A much more comprehensive set of methods are available, depending on radionuclide, compound, mode of administration, etc. This discussion is much too narrowly focused.
Line 1360
Not clear how E is useful as an initial indicator of tissue reactions. It isn’t and should not be.
Line 1525
Not clear how this is relevant to the use of E.
Line 1567-1569
It seems a bit confusing as to why propose to use “collective dose” in the situation discussed, if it is then going to be split according to dose range, geographical location, time-course, etc. Maybe the committee could reconsider their suggestion and just minimize use of collective dose entirely.
Line 1598
“volume averaged” is incorrect. See IEC 60601-2-44 Edition 3, definition 201.3.212.
Line 1599, 1603
Not all are measure-able. Kerma-area product and dose-length product are not measure-able themselves but rather are calculated from measured quantities.
Line 1616
“Effective dose has provided a useful reference for the improvement…” What is meant that E is a ‘reference’? This needs to be clarified.
Line 1620-1632
These sections give all of the reasons why it is not intended to use E as an approximate indicator of possible risk, but are followed by 1632-1636 that indicates that evidence is presented to counter these rather important and reasoned barriers to such use.
Line 1628
Does it “ignore the uncertainties” or rather simply provide a point estimate without attempting to quantify confidence in this estimate?
Line 1632
The statement, “…evidence is presented in this chapter in support of the use of effective dose as an approximate indicator of possible risk associated with medical procedures, showing that difference between estimates of risk based on effective dose and estimates based on the use of organ doses and age-, sex- and cancer-specific risk estimates are predictable and generally not large,” is problematic. The relevant evidence presented (for example in Figure 5.1) seems to indicate just the opposite, that is, that risk estimates based on organ doses and age-, sex- and cancer-specific risk estimates differ considerably from those based on effective dose. This apparent discrepancy should be addressed, specifically, the data supporting the foregoing statement should be identified and presented more clearly.
Line 1636
“…are predictable and generally not large.” How are they predictable? Not large when compared with what measure? Note that UNSCEAR and others have said that in low dose region the uncertainty associated with risk estimates is in the range of +/-300%!
Line 1637
Clearly indicate how these examples of the limitations/uncertainty inherent in E make it inappropriate to convey absolute risk.
Line 1723
A reference would help support the statement that E is not the best quantity for making comparisons between doses for similar techniques applied in different departments or institutions.
Line 1772-1780
The concept or practice of medical dose tracking may not be appropriate as it will inevitably lead to medical decision-making for individual patients based on their dose history rather than on medical necessity/medical benefit. Decision-making regarding imaging procedures should be based exclusively on the following criteria: 1) Is the medical information being sought essential to the appropriate management of the patient? If Yes, then 2) Can the same information be obtained by alternate, non-radiationbased but comparably non-invasive and non-morbid procedure? If No, then 3) Is the procedure being performed in an optimized way such as to minimize patient dose without compromising information being sought? If Yes, proceed with imaging procedure.
Line 1791
Paragraph (111) is very confusing. “…not intended as a measure of risk to individuals…”, “…considered reasonable…”, “…approximate indicator”, “…for risk communication in general terms…”, “…with appropriate caveats for individual patients…” Presumably the reason appropriate caveats are needed is that the uses identified may not be reasonable.
Line 1825
Paragraph (115) is very general discussion that does not draw upon or reference the latest literature on communicating with patients. Some of that literature suggests comparisons are not at all helpful.
Line 1835
Citation needed “The potential risk from medical exposures is generally lower than for a reference population due to the higher average age of patients and competing disease related risks with reduced life expectancy…”.
Line 1845
“Minimal” sounds like it is less than “extremely low.”
More granularity should be considered for the <0.1 mSv category. There is a big difference between 1 pSv and 0.1 mSv. Perhaps 1 pSv is “negligible” but 0.1 mSv is not. It’s unclear where to draw the line.
Table 5.2 is problematic. ICRP’s assignment of individual procedures to these broad levels, which would miss differences in procedures with typical doses of 2 vs. 10 mSv but create a difference between 9 and 12 mSv, could lead to incorrect perceptions about relative risks of procedures. There are few procedures with doses in the 50-100 mSv range making this wasted space in the dose comparison landscape. Perhaps more granularity in the middle would be useful in terms of grouping imaging tests by dose level and avoiding having such broad categories that the difference between categories is perceived as being of great significance even for tests with similar E. In the table as it reads now, CT of combinations of chest, abdomen, and pelvis are in the 1-10 mSv category whereas CT scans of chest, abdomen, and pelvis are in the 10-100 category. Reference the typical doses for procedures, as in e.g. Mettler F et al, Effective doses in radiology and diagnostic nuclear medicine a catalog. Radiology 2008; 248 254-263 and for cardiac procedures Einstein AJ et al. Patient-centered imaging shared decision making for cardiac imaging procedures with exposure to ionizing radiation. J Am Coll Cardiol 2014; 63 1480-1489.
Line 1897
ICRP should include consideration of benefit and risks, see Zanzonico https//www.ncbi.nlm.nih.gov/pubmed/26808890 as an example reference.
Line 1899-1900
Add “Estimated” to beginning of table’s title, i.e. “Estimated total lifetime risks…” Also indicate that this is based on UK imaging doses. Interestingly, the results shown from 30-50y appear to average about 5%/Sv (the nominal ICRP public risk coefficient) across all examinations. What is being shown here that is relevant and important?
Line 1904-1905
Add “Estimated” to beginning of table’s title, i.e. “Estimated total lifetime risks…” Also, the risk data is shown as derived from Asian population, what about the imaging dose data, is that Asian population or UK?
Line 1914
Add “Estimated” to beginning of figure’s title, i.e. “Estimated total lifetime risk…” Also, why only show the results of the Asian risks?
Line 1942
Here E is characterized as the central radiation protection quantity, whereas in line 830 ,absorbed dose is characterized as the fundamental physical quantity, and in line 186, absorbed dose, equivalent dose, and effective dose are “the dosimetric quantities used in radiation protection”. These differences are subtle and a more coherent approach, introduced at the outset of the document around 186, would benefit readers. Consider something in 186 like “The fundamental dosimetric quantities used in radiological protection across radiation exposure scenarios are absorbed dose (D), which is the fundamental physical quantity, equivalent dose (H), and effective dose (E), the central radiological protection quantity in most settings. The unit for D is given by the special name of gray (Gy), and the unit for H and E is given by the special name of sievert (Sv); both Gy and Sv are derived units in the International System of Units (SI) equal to 1 J kg-1.” Also, given the “demotion” of equivalent dose in this document (see e.g. 1978), perhaps it is no longer “fundamental” and should be removed here.
Line 1963
Here absorbed dose is termed the “primary scientific quantity from which E is characterized” whereas in 830 it is called the fundamental physical quantity. Harmonization of descriptive terminology as above would be beneficial.
Line 2055
Just because E is in widespread use in medical practice as an approximate indicator of risk, does not justify its use. This use is still unintended. Why does this document appear to give widespread support for just such assessments and usage.
Line 2059
“…with additional consideration of variation in risk with age, sex and population group.” Aren’t these just the sort of individual characteristics that would appear to make E not an appropriate indicator of risk, especially in the low dose regions (<100 mSv) where uncertainties are very large?
Line 2060
Sentence reads “In the majority of situations, simple qualitative descriptors of the possible risk associated with effective dose will be sufficient to inform judgements.” In view of concerns expressed above with the arbitrary thresholds and broad ranges in the proposed system of simple qualitative descriptors (Table 5.2), there is doubt that these “simple qualitative descriptors” will indeed be sufficient to inform clinical decisions such as comparisons between different tests or testing strategies. This statement ascribes undue importance to these descriptors.
Line 2068
As above, should also mention comparison between testing strategies and different tests or protocols using the same modality. An example of the latter would be comparing options for a nuclear medicine test which can be performed using different radiopharmaceuticals.
Line 2086
“…understand the possible risks…” How can the possible risks be understood? Perhaps what is meant is theoretical assessment of potential risks under certain narrowly determined set of assumptions.
Line 2090
paragraph (132) this is inconsistent with ICRP Publication 103 paragraph (105) that notes not to use E for high doses.
Line 2105
Need to ensure consistency with ICRP Publication 103, see Executive Summary paragraph (k) as this section differs.