The Use of Effective Dose as a Radiological Protection Quantity

Draft document: The Use of Effective Dose as a Radiological Protection Quantity

Submitted by Virginia Tsapaki, International Organization for Medical Physics
Commenting on behalf of the organisation

International Organization for Medical Physics (IOMP) has formed a group of experts to provide feedback on the document.

Group of experts

Maria-Ester Brandan, Mexico

Olivera Ciraj Bjelac, Serbia

Nadia Khelassi Toutaoui, Algeria

Mika Kortesniemi, Finland

Ehsan Samei, USA

Virginia Tsapaki, Greece (Chair)

Comments from Group of experts

All experts agree that the draft report is generally well written and coverage is appropriate for the intended use. This document offers a much needed and somewhat overdue consideration in the use of effective dose (ED) in medical imaging. It will be valuable for scientists, regulators, employers and radiation workers worldwide. It nicely identifies issues that need further guidance and clarification and to the certain extent provides clarification on the use of effective dose. Clarified role of ED in dosimetry, optimization and risk assessment helps multi-professional science and medical community in their practical communication and daily work, and also in their education, training, research and development projects. Experience has shown that ED which has been defined and introduced by ICRP for risk management purposes is widely used in radiological protection and related fields beyond its original purpose, incorrectly in some cases. To expand the publication 103’s recommendations with an important focus in medical exposures, some questions have arisen regarding practical applications, highlighting a clear need for further guidance on specific aspects.

It is made clear in this report that while doses incurred at low levels of exposure may be measured or assessed with reasonable accuracy, the associated risks are increasingly uncertain at lower doses.

Bearing in mind the uncertainties associated with risk projection to low doses, E may be considered as an approximate indicator of possible risk, with the additional consideration of variation in risk with age, sex and population group.

Absorbed dose is the most appropriate quantity for use in setting limits on organ/tissue doses to prevent tissue reactions (deterministic effects).

It is suggested that will be more appropriate for limits for the avoidance of tissue reactions for the hands and feet, lens of the eye, and skin, to be set in terms of absorbed dose (Gy) rather than equivalent dose (Sv)

Having explicitly mentioned the importance of the document all experts agree that the report is unclear on the following items:

It is well recognized that E was designed as a radiation protection quantity, drawn from population based characterization of risk. In practice E is ascribed to an individual, even though the construct is population-based. The application to patients undergoing medical imaging procedures suffers from the same ambiguity and confusion. Should we apply E in medical exposure? Although the term of E is extensively described, the authors not do make clear simple statement on whether or not to use E as all us today in every day clinical routine. The report could benefit a lot from a clear recommendation in the conclusions section.

It is unclear if the current report explicitly encourages or discourages the use of ED in Diagnostic Reference level (DRL) applications. This is particularly needed as previous ICRP reports explicitly stated that ED is NOT a good metric of DRL.

Risk communication is a key necessity of irradiation applications. It would have been relevant if the current report could speak to that.

The report is vague in clarifying its main recommendation.

It would have been much value if the current document could clarify the role and value of organ dose, and cite key recent publications in that regard. It would still add the value of the report if the role of organ doses and practical application of sex and age specific factors for risk assessment could be clarified more.

For medical procedures or other situations in which a single radiosensitive organ receives the majority of the dose, such as the breast in mammography, or the thyroid from therapeutic administration of iodine, mean absorbed doses to the tissues of interest should be used rather than effective dose.

The report will benefit from a consolidated section on what is needed – perhaps through a single section at the end of the document, with math-based formalism to avoid confusion in interpreting the language of the report.

The report will benefit from discussing the uncertainty in the E estimation.

Conversion of application specific dosimetric quantities used in diagnostic and interventional radiology to the effective dose could be more elaborated, with comments on the associated uncertainties

10. The use of effective dose in accidents/incidents with patients in medical exposure could be more elaborated, with recommendation when organ dose are complementary used

11. The last years, a number of sophisticated and rather expensive software are introduced in the global market and installed in numerous hospitals around the world that track all technical data from the imaging modality DICOM report. Some also calculate organ doses and E. All of them refrain from providing scientific data on these calculations. The report could also include a more explanatory and clear recommendation on the use of such software for the benefit of readers and healthcare providers, managers and decision makers related to such investments.

12. Use of ED in nuclear medicine could be more clearly addressed

13. Use of ED in radiotherapy, in the context of non-target organs could also be mentioned.

14. Use of ED in embryo/foetus in patients and in occupational exposure should be mentioned (planned or unplanned exposures in for pregnancy).

15. Use of ED in paediatric patients, should also be mentioned more explicitly.

16. In the section 3.4. (ED), comment specific to medical exposure could be added.

17. Dose coefficients mentioned in the section 3.5 are related to the occupational and public exposure. However, those related to the medical exposure in nuclear medicine could also be mentioned.

18. Section 3.6 and similar, deal with organ dose, however the link to ED could be mentioned as well.

19. Section 3.7 deals with current operational quantities. Possibly, the new joint ICRP/ICRU draft recommendations on operational quantities could be mentioned, as it significantly revises the current concept.

20. The use of effective dose as an approximate indicator of stochastic risks can be reasonably extended beyond medical applications to, for example, consideration of protection options for accidental exposures of workers and members of the public.

21. The most essential part of the text is or should be “summary and conclusions”. All main points must be clearly stated with a sense of completeness in order to pass to the reader the relevant message. The current document needs to be further elaborated to fulfill this objective. The suggestion could be to have simple straightforward sentences in bold in each paragraph dealing with different subject.

Also specific comments below, indicating the page and row of the related text part.

page 8, row 220: text should be clarified as follows: “exposed in the same way, regarding the equivalence of organ/tissue equivalent doses.”
page 9 row 227: please clarify “dose coefficients” already here – as dose coefficients (Sv Bq-1) for intakes of individual radionuclides by workers and members of the public (ref. chapter 3.5) – because the term is used frequently in the following text.
page 9, row 270: consider adding: “population group, and dose distribution heterogeneity.” – to note that if dose in modality A is providing very heterogeneous dose distribution within a specific radiosensitive organ, and modality B does not, they have potentially different detriment although the average organ dose could be the same.
page 11, row 301: correct the name “McCullough”, should be “McCollough”.
page 14, row 467: please, specify what risk is here referred to, e.g. death.
page 15, row 469: please, clarify briefly (one sentence should be enough) the reverse causation.
page 16, row 539: clarify “anatomical site” or “tissue/organ site”.
page 16, row 555: “morbidity and suffering” would be good to clarify further, even briefly.
page 17, row 576: justification to “use of incidence rather than mortality data” would be good to clarify briefly in this paragraph.
page 18, row 620: It would be helpful to explain the column titles a bit more in the Table 2.1 caption or footnote. Thus, the readers do not necessarily have to go to see the Report 103 for that.
page 19, row 660: Uncertainties which are mentioned in the row 649 would be great to clarify in the Table 2.3. along with the wT values. That would give a better perspective to interpret the numbers and understand the magnitude of uncertainty more clearly.
page 25, row 830: correct typo “fndamental”
page 34, row 1203: correct typo “Rannikko”
page 47, row 1789: Recording of organ doses by dose tracking systems would also provide significant data source for the future research – facilitating modality based technical studies, patient specific radiation dose studies and epidemiological risk related studies. This potential should be mentioned.
Lines 185-187. It says: The dosimetric quantities used in radiological protection are absorbed dose (D), with the special name of gray (Gy), and equivalent dose (H) and effective dose (E), both with the special name of sievert (Sv); the SI unit is J kg-1 in each case. The wording gives the impression that gray is the name of D, and sievert that of H and E.
In Table 2.1 column 6 should say "relating to column 2", since column 1 lists the tissues.
In the text "tissues" and "organs" are used indistinctly.
Reference to ESAK in Line 1200 is confusing. It reads that ESAK is a measure of the dose to the skin surface relative to air, while its definition is that of kerma to air measured on the central beam axis at the position of the patient surface.
In Lines 1345 and 1419 the expression man-made radioactive materials is used. It would be more appropriate to replace by radioactive materials of anthropogenic (or human) origin.
Paragraph 64 on page 34 could be revised to address more methodology for effective dose assessment in medical exposures (diagnostic and interventional radiology, nuclear medicine), reference to ICRU Report 74 should be provided, including software tools for effective dose assessment
In many cases, like in paragraph 76 on page 37, the very nice examples are given, however clear recommendations are still missing
Similarly, on page 45, paragraph 102/103 and paragraph 108 on page 46, could be additionally clarified in the context of use of organ vs effective dose

Additionally, IOMP has requested feedback from its National Member Organizations (NMOs) on the subject as well. Representatives of NMOs were asked to provide answers to a structured questionnaire than asking them to provide general comments.

Questions that had to be answered:

Does the report help you in solving your problem?

If yes, what problem does the report solve?

Do you encounter any other problems that ICRP should have attended to in this document?

What are your expectations from ICRP on developing radiological protection quantities?

Responses to questions above from NMOs

The responses showed that NMOs consider the ICRP report to be helpful.

According to NMOs, the report solves the issue of: a) equivalent dose (H) (the term can cause confusion to many people as far as the level of organ/tissue dose that can cause a determination effect) and b) improvement of radiation protection procedures .

NMOs do not encounter any other problem that ICRP should have attended to in this document.

Their expectations include: a) focus on radiation dose levels in Nuclear Medicine medical field and possible deterministic effects and b) underline the importance of ICRP organization on radiation protection.

A detailed report was received by the Netherlands Society of Medical Physics (NVKF).

- Does the report help you in solving your problem?

Yes and no.

This report is an extensive review of existing ICRP publications and scientific literature, it does not present new information but it does provide clarity for those confused. This report complements what has been stated in ICRP publication 103 about dose quantities such as absorbed dose, equivalent dose and, in particular, effective dose. Although in essence in this draft report the same is said about dose quantities as in ICRP publication 103, the draft is completely dedicated to dose quantities and elaborates on the (correct) use of them. Therefor the draft report has an added value for the medical physics community, according to the NVKF (Dutch Society for Medical Physicists).

- If yes, what problem does the report solve?

Examples of incorrect use of effective dose in the medical field are

Risk estimation of individual patients and volunteers, without noticing that effective dose is only an indicator of possible risk, or without considering variations in risk with age, sex or population groups (addressed in the draft report e.g. in lines 299, 323, 452, 521, 1606, 1752, 1767)
Risk projection of populations of patients, without noticing that collective effective dose is not a tool for epidemiological risk assessment (addressed in the draft report e.g. in lines 1228, 1554)
Comparing doses from similar techniques or modalities, where technique or modality specific dose quantities should be used (addressed in the draft report e.g. in line 1723)

To support and encourage the correct use of dose quantities, the report extensively describes the history, concepts, assumptions and uncertainties of the quantities. It also discusses proposed alternatives in literature (addressed in the draft report e.g. in lines 676, 1623).

In addition, a major change is made by proposing that absorbed dose should be used as quantity for limiting organ/tissue doses and therefor equivalent dose should be discontinues for this purpose (lines 190, 195, 454). Equivalent dose than only remains a step to calculate effective dose (line 993).

Finally, risk communication is getting more and more important in the medical field. This draft report addresses this explicitly (from line 1790).

In summery: ICRP takes its central role in the discussion to provide clarity – the use of E is now clarified; equivalent dose is now abandoned and E’s role in risk communication is now on central stage.

- Do you encounter any other problems that ICRP should have attented to in this document?

The ICRP acknowledges the uncertainties associated with risk inference at low doses from medical procedures. It would be helpful to quantify these uncertainties and describe their effect (and in general the absence of effect) on the justification of medical procedures. In general, medical procedures do more good than harm. Even when taking these uncertainties in radiation risk into account.

The report also enters the field of medical research exposure, a field that used to be covered exclusively by ICRP report 62. Differences between the current report and the E associated risks in ICRP 62 cannot be explained by carefully reading the present text. This undermines the present text as it hampers discussions, training and teaching (referring) physicians and (medical) researchers, in research and in clinical settings.

- What are your expectations from ICRP on developing radiological protection quantities?

The radiological quantity effective risk, including its uncertainties, should be introduced.The Netherlands Society of Medical Physics also made a number of detailed comments as per the tables below:

Line number	Type of feedback (editorial / content)	Feedback	Question or proposal for improvement
Main points / page 8 / first bullet / lines 185-187.	content	It’s incorrect to state that the dosimetric quantities have special names.	The units of these quantities have special names.
274	editorial	In considering doses to..	This sentence probably deserves a bullet of its own. Separate point made here
Section (26) / lines 730-736	content	In general the effect of genetic differences might be unknown. In specific cases these effects are known. For example in breast cancer.	Please describe how to incorporate this knowledge in specific cases for the justification and optimization of medical procedures.
930	editorial	..poviding advantage of providing continuity..	Not changing something for providing continuity with earlier work does not seem the best argument. A more intellectual / contentual argument against the Thomas and Edwards (line 920) critique?
1084 + 1119 + 1309	content	Equivalent doses of 500 mSv .. 70 micron	In daily practice it is often difficult to relate the yearly 500 mSv equivalent dose limit to hands of workers (e.g. interventional radiologists) to the stochastic effect/chance of inducing skin cancer. Opportune to add information/ current state of affairs into this ICRP report?
1309	content	Skin dose assessment to improve effective dose estimate seems to challenge the approach as suggested for patients. Different approaches for workers and patients may prove confusing.	In Line 1309 it is suggested to use additional skin dose assessments based on measurements to provide a better estimate of effective dose. This seems to be contradicting with the remark in line 1660 through 1662 (true.. for medical exposures, but still) estimates of organ or tissue dose should be used instead of effective dose.
1360	content	Whether effective dose relates to possibility of later tissue reactions will depend on type of radiation/exposure situation during accident.	Role for effective dose, alone, in context of initial tissue reaction triage? Please clarify, explain in text. Type of radiation and e.g air kerma as an alternative to effective dose for initial characterizations in accident situations?
Section (94) / line 1595.	content	The recorded quantities do not describe the radiation dose received by patients because these are patient (size) dependent.	Replace by: “The emitted dose delivered by the machine in diagnostic …”
Section (95) / lines 1614-1616	content	It is true that the effective dose is used to aid in justification of medical procedures but in the end it is the associated risk that counts.	Please acknowledge the importance of the associated possible risk when justifying a medical procedure.
Section (96) / lines 1627-1629.	content	It might be true that the approach ignores the uncertainties in associated risks, this does not make the approach incorrect or less correct than the effective dose approach. The effective dose (instead of risk) approach has to deal with the same uncertainties and ignores them as well.	Instead of abandoning the effective risk approach, embrace it and incorporate the known uncertainties.
Section (96) / line 1632	content	Where is the evidence presented exactly?	Add a reference.
Section (96) / line 1636	content	When is a difference ‘not large’?	Put the differences in risk estimates into perspective. How are these estimates used and do these need to be accurate?
Section (97) / line 1640	content	One cannot justify a medical procedure without translating the effective dose into a risk. One can optimize a procedure without the translation to risk.	Acknowledge the need to associate a possible risk with a certain effective dose when justifying a medical procedure.
Section (98) / line 1660-1662	content	In general, every medical procedure is limited to one anatomic area. It is stated that organ or tissue dose should be used instead of effective dose.	This statement is not worked out in much detail and raises the following questions: when should organ dose values be used instead of effective dose (justification, optimization or …); why should organ dose values be used? And how should these be used? Please clarify the rationale of this paragraph.
1686	editorial	…are included in many guidelines for…	Please provide references
Section (101)	content	When using effective dose in children, one must take to effects into account: 1) the change of dose distribution in the body for a given exposure level; 2) the change in risk due to higher radiation sensitivity and/or longer life time. It is often not clear whether both effects have been taken into account.	Please address both effects.
Section (107) / lines 1751 – 1752 And Section (108) / lines 1767 - 1771	content	This means that the quantity of importance is effective risk instead of effective dose.	Please acknowledge the usefulness of effective risk.
Section (109) / lines 1773 - 1777	content	It is not correct to suggest the recording of the patient's accumulated dose because the number of patients who receive repeated imaging procedures has risen.	One can suggest considering the information (not the dose) obtained from previously performed procedures when requesting a new procedure.
Section (109) / lines 1777 - 1780	content	One might think that these recorded quantities are of use when justifying a new procedure. This is incorrect: the possible risk of the new procedure does not depend on the dose of previously performed procedures.	It should be noted that for the justification of a new procedure, knowledge on the accumulated radiation exposure is of no use.
1842	editorial	Risk of what exactly? The actual risk communicated through effective dose is unclear in the present text. Risk of cancer vs risk of dying of cancer (cf. table 2.1 line 620)? Relevant because ICRP report 62 does clarify that point, but presents slightly different numbers. ICRP62 is used by Ethical committees: risk of cancer (concept) should preferentially be the same in the current report.	What risk is actually communicated through effective dose – in the way the present report is doing. Risk of cancer or additional risk of dying of cancer. Please clarify throughout chapter 5. ICRP report 62 (p.11 and Table 2) reports ” … be noted that the risk is the total detriment from the exposure; namely the sum of the probability of fatal cancers, the weighted probability of non-fatal cancers and the probability over all succeeding generations of serious hereditary disease resulting from the dose.” ICRP62 is used by Ethical committees: risk of cancer should preferentially be the same in the current report. Differences in risk numbers between the current report and report 62 should be clarified.
Section (117) / line 1880	content	This statement is valid for a particular age and sex. It seems that this is ignored in Section (96), line 1634.	Please rephrase.
Section (118) / line 1890-1893.	content	Here the uncertainties in associated risk are used to prefer effective dose over effective risk. However, on many places in this report (including sections 107 and 108), one suggests using age and sex specific risks.	Please make clearer when to use effective risk instead of effective dose.
2081-2089	editorial	Related to previous point: Relative risks per age-group are different in this report as compared to ICRP 62, this warrants clarification as ICRP 62 is still actively used in ethical review processes.	ICRP report 62 states: “For investigations involving children the detriment per unit dose is 2 to 3 times larger than for adults; for people aged 50 years or over when exposed to the radiation sources it is only about l/5th to l/l0th of that for younger adults. Clearly if those to be exposed are suffering from serious, possibly terminal disease then the likely expressed radiation-induced risk will be even lower.” This report: “With this important caveat, it can be concluded that when considering most x-ray examinations, lifetime risk of cancer incidence per Sv may be around twice as great for the 0-9 years age at exposure group than for the 30-39 years group. For patients in their 60s, the lifetime risks from most examinations are estimated to be about half those for patients in their 30s, falling to less than one-third for patients in their 70s and about one-tenth for those in their 80s. Used appropriately, such information is of value in helping clinicians understand the possible risks associated with examinations and assist in communication with patients. In considering doses to patients having diseases with poor prognoses, life-expectancy will be a consideration in evaluating radiation risks.

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