The Use of Effective Dose as a Radiological Protection Quantity

General Comments

The draft document is scientifically unsound, poorly written and very confusing to implement.

The document pretends to expand the use of Effective Dose (E) beyond its original purpose, to quantify risk in medical exposures. It states that just by taking account of sex, age, and population group, E can be used as an indicator of risk without giving any order of magnitude for the uncertainties involved. This is problematic as E was defined for radiation protection purposes only, based on the LNT hypothesis and using judgmental factors such as w_R and w_T which are dose and dose rate independent.

The document is written very confusedly, with a lot of repetitions. Sections 2, 3 and 4 are a summary of previous ICRP previous documents with the aim of clarifying certain aspects. Instead, sometimes they confuse them. The sections should be rewritten for greater clarity and focus, replacing many statements by proper bibliographic references. Furthermore, the dosimetry section should be revisited, since some terms are improperly defined.

The real problem of the document is Section 5, which seems to be written by two people of conflicting perspectives. Many sections contain two contradictory messages. The first one insists that E can be used for medical exposures; the second part of the same paragraph provides caveats on when one should use organ or tissue doses instead. One of the caveats clarify that when the radiation field is limited to a specific region, organ/tissue doses are better. The problem here is that in radiation therapy and medical imaging (even using radiopharmaceuticals), only limited portions of the body are irradiated. Thus, one should always use organ doses!

In the past, organ doses were difficult to determine in medical imaging, but with the advent of the DICOM Standard Patient-Radiation Structured Report, the task is simplified significantly. It seems that the ICRP document should address that. Of course, these dose determinations have uncertainties. Their order of magnitude should be given in the document.

To illustrate some of the problems summarized above, I have commented on specific sections below. 

Specific Comments

Line

It says

Comments / Suggested changes

111

It will be more appropriate for limits for the avoidance of tissue reactions for …

The sentence needs English editing. Perhaps it can be changed to: "It will be more appropriate for limits to avoid tissue reactions for…"

118-121 & 267-270

Bearing in mind the uncertainties associated with risk projection to low doses or dose rates, 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. 

This is statement is unscientific. How should one interpret "an approximate indicator of a possible risk"? To start with, E was not introduced as a risk indicator, it was meant as a quantity that could integrate dose contributions from several radiation sources to various areas of the body using judgmental factors and thus, establish dose limits, for protection purposes ONLY. Risks should be based on epidemiological findings. Furthermore, the text does not provide any values for the uncertainties mentioned. Durand et al (2012) assigned a 500% uncertainty when effective dose is used in medical exposures.

11-1590

These sections cover material most of which was previously published by the ICRP. Unfortunately, the text is written in a confused manner with unnecessary repetitions. It should be summarized and refocused.

666-712

2.6. Age- and sex- specific cancer risks 

Why aren't the values of BEIR VII used?

762-825

 The addition of risks from alpha particles is welcome, but what about beta particles? In radionuclide therapy, many beta emitters are used today (Lu-177, Y-89, etc.) ...

945-946

The use of equivalent dose as a distinct protection quantity is not required.

Excellent conclusion. I fully agree.

970-976

The paragraph uses mSv for tissue reactions. It should use mGy. Also, the phenomenon of cataract induction may be mentioned here.

1046-1047

Annexes and a CD provide detailed supporting information 

Where are the Annexes?

1200-1201

(ESAK, Ke), which is a measure of the dose to the skin surface relative to air 

The definition given is wrong. ESAK is the entrance-surface air kerma on the central x-ray beam axis at the point where the x-ray beam enters the patient (ICRU 74, 2005).

(KAP, PKA), which is the product of the air kerma incident on the patient and the area of the X-ray beam at the skin surface 

This statement is not necessarily wrong, but P_KA does not have to be defined at the skin surface, since it does not depend on the distance to the x-ray target. In fact, most measurements are done placing the KAP meter at the end of the collimator.

1212-1213

Such assessments give an indication of the radiation doses to patients that are sufficient for most requirements. 

What requirements? For medical exposures, organ doses are necessary. The dose indices given in paragraph (64) are acceptable for DRLs, they do not represent patient doses.

1230-1232, 1258-1260 and 1537

The concepts re collective dose are repeated, maybe it is enough to put them once.

1560

and consider uncertainties 

Nowhere in the document, it says how large are the uncertainties!

1627-1629

this approach ignores the uncertainties associated with risk inference at low doses based on epidemiological observations of populations exposed to higher doses. 

Certainly, Brenner's effective risk has uncertainties. Are these larger than the ones inherent in effective dose? No uncertainties regarding effective dose are listed in this document

1632-1636

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. 

This "of the cuff" statement is not true (where is the bibliographic reference?). For example, if the radiation field involves the eyes, the eye lens dose can be much higher than the effective dose. Another example was presented in lines 2076-2077.

1660

When imaging is limited predominantly to one anatomic area 

This is usually the case. One does not image the whole body purposely. Even in nuclear medicine, when looking for metastases, the radionuclide concentrates predominantly in one or various organs.

1661

estimates of organ or tissue dose should be used instead of effective dose 

As a consequence, this recommendation should apply to medical imaging in general.

1701-1702

the effective dose is suitable for use in straightforward comparisons of doses from different techniques 

While this statement is true, organ doses can also be compared, as some Cynthia McCollough publications show.

1703-1714

This paragraph (103) is against ICRP principles. The justification of a practice (in this case the choice between a CT or a planar radiograph should be clinically based, not dose-based. Apart from the fact that a radiograph provides a 2-D image, and the CT scan, a 3D image; the chosen exam should follow clinical referral guidelines. Only the radiologist should decide if the CT is necessary from a clinical point of view.

1721-1722

It is inappropriate to invoke the ALARA principle in medical exposures. ICRP 103 and the International BSS have stated very clearly that the dose should be commensurate with the clinical objective of the procedure.

1737-1742

To select kV and/or filtration based solely on dose, without considering the impact on image quality is wrong. Lowering the kV improves image contrast. The study may demand great low contrast resolution.

1747-1750 vs 1750-1752

The first sentence says that effective dose is OK, the second (final) sentence that is not. These contradictions occur often in the document and will confuse the reader!

1761-1762

In situations of unintended exposure, where the dose level is low, a broad assessment in terms of effective dose will usually be sufficient.

That may be true depending on the radiosensitivity of the organ irradiated. Again, the eye lens is a very sensitive organ...

1763-1771

The instructions in this paragraph are totally incomprehensible and impossible to carry out. Individual risk cannot be inferred from effective dose, which is based on a population measure.

1772-1780

Tracking of patient doses 

The paragraph contains a lot of errors. Most dose tracking methods are based on DICOM standards, not "measured dose quantities".

>1780, <7181

Here would be a good place to discuss the use of the Radiation Dose Structured Report (RDSR), especially the new Patient-RDSR. 

1788

effective dose to a reference person 

Paragraph 110 is too superficial. How does one find "the reference person"? Perhaps there should be references to published guidelines

1791-1793

Effective dose and risk communication 

Paragraph (111) uses terms such as "not intended", but "reasonable", to "approximate" risk "in general terms". And then suggests the use of caveats. What are these caveats? As I said above, one should be able to give uncertainties.

1802-1804

Education and training

Clinicians may not understand effective dose, but will understand the potential detriment to organ doses, as they are familiar with the anatomy and physiology of organs and tissues. ICRP 118 should be taught in medical school.

1805-1810

As for cancer, benefit vs risk ratios should be developed and taught. LNT is very easy to explain.

1811-1849

Communication of doses and associated health risks 

I disagree that only effective dose can convey risk. Organ doses can too.

1847

^b Effective doses based on UK for diagnostic procedures and ICRP (2010b) for interventional radiology 

Please, provide the reference

1886-1893

Paragraph (118) compares risks vs age. What about absolute risks? What are the uncertainties of the "doses" inferred by the proposed methodology?

1902-1904 & 1907-1909

Tabulated values are risk coefficients (per Sv), not absolute measures of risks from the various procedures from which the doses delivered are in the mSv range or lower.

Please, clarify the meaning of this sentence and how the table is to be used.

1921-1935

This paragraph is excellent, the best in the whole section of Medical Exposures. But it contradicts what was said in the previous sections and will confuse the reader.

1935-1936

Uncertainties in both dose and risk estimates should be considered.

It would be important to give some figures. Doses can have tolerances of about 35%. What about risk estimates? Durand et al (1212) calculated an uncertainty of 500% for effective dose in medical imaging

1964-1966

Absorbed dose (D) in gray (Gy) should be used to set limits on organ/tissue doses to prevent tissue reactions (deterministic effects) rather than equivalent dose (H) in Sv which relates to cancers and hereditary diseases (stochastic effects).

This is an excellent recommendation, consistent with past usage.

1974-1982

I fully agree with Paragraph (123). Only effective dose should be expressed in mSv to avoid confusions.

2000-2004

it is notable that estimated differences in lifetime risk of cancer incidence between males and females and between age groups, as illustrated in Tables 2.4 and 2.5, are not large in the context of the practical application of the system of protection at low doses and uncertainties associated with estimates of risk at low doses.

Without indicating what these uncertainties are, the sentence is meaningless.

2005-2006

Protection would not be improved by introducing separate considerations for males and females 

That is not universally accepted. NASA uses different dose limits for male and female astronauts.

2031-2033

for doses in excess of 100 mSv (or more precisely, absorbed doses to organs and tissues > 100 mGy) delivered at high dose rate, the DDREF of 2 applied in determining solid cancer risk at low doses will not apply, so that risks may be somewhat greater than might be assumed on the basis of Publication 103 (ICRP, 2007a) nominal risk coefficients.

How much greater will be the risks for doses > 100 mGy delivered at high dose rate? 50%, 100%, several orders of magnitude???

2055-2057

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 uncertain. 

No, it is not made clear at all, as risk uncertainties are never quantified

2062-2066

It is emphasized that use of E as an approximate measure of possible risk is not a substitute for risk analysis using best estimates of organ/tissue doses, appropriate information on the relative effectiveness of different radiation types, and age-, sex- and population-specific risk factors applying to the organs/tissues at risk, with consideration of uncertainties.

This statement seems to contradict the previous one. How can the normal reader of your document decide whether effective dose is sufficient to infer risk, or a risk analysis is to be done? And how will the normal person assess the uncertainties?

2070-2071

(130) E can be used in medical applications to: compare doses from different diagnostic 

No, effective dose is not the parameter to be used for justification of radiological procedures, it can be used as an optimization tool to refine the procedure techniques

2073-2075

for comparisons of doses from the same procedure in different facilities and for setting diagnostic reference levels, measurable dose quantities are preferable.

Fully agree. But it seems to contradict previous statements.

2076-2087

How can this information regarding cancer risk dependence on age be valuable to a patient if neither the absolute values of risks or the uncertainties in the estimations are given?

2090-2096

Again, the paragraph seems to contain contradicting recommendations. Yes, effective dose is OK, but if the irradiation is limited to an organ (which is common in medical imaging), determine organ doses.

2113

consider uncertainties

Something that this document fails to do.

2225-2226

Interim edition

The reference should be changed to the final edition, published in 2014

Add reference

DURAND J, DIXON R, MORIN R. Utilization Strategies for Cumulative Dose Estimates: A Review and Rational Assessment. J Am Coll Radiol 2012;9:480