Comments on the ICRP Draft Document:
Operational Quantities for External Radiation Exposure
On behalf of the Austrian Radiation Protection Association:
Alexander Brandl*, Michael Hajek, Christian Hranitzky, Hannes Stadtmann, Andreas Steurer
alexander.brandl@colostate.edu
Dear Colleagues,
We thank the International Commission on Radiological Protection (ICRP) and the authors of the draft document on Operational Quantities for External Radiation Exposure for the opportunity to review and provide feedback on the current draft. We believe that the current document provides a comprehensive proposal for a new approach to defining operational quantities for the purpose of converting measurements of radiometric and dosimetric quantities to protection quantities. We appreciate the significance of the work and the effort by the authors and research groups involved in preparing the data presented, and commend the authors for their diligence and hard work.
We have identified a few general and some specific thoughts or comments on the draft document which we would like to share with ICRP.
General
We understand that the document in its current form is considered a draft document. Still, we would like to encourage ICRP to conduct a thorough editorial review prior to publication of the document. Language, grammar, and punctuation, and with those the flow and consistency of the document might benefit from such a comprehensive review. The current document appears to be drafted by a group of authors with different writing styles which might be perceived as distracting by some readers. The word “give” or “gives” is used rather extensively in the text; and while it is not necessarily incorrect in the context, other terminology might allow for some stylistic alternatives. For example, tables and figures may “show” or “display” certain data, results may be “provided”, and computations may “result” in certain output. The Oxford comma seems to be applied inconsistently and / or sporadically. And we generally recommend that units associated with a numerical value (magnitude) of a quantity be delineated from that magnitude by a blank. On various occasions, singular and / or plural words appear to be used incorrectly; we will list some of those instances in our more specific comments, which, however, may not be completely exhaustive.
The current document radically changes the previous ICRU concept where operational quantities have exact and physically rigorous definitions (i.e., by using simple geometrical calibration phantoms and a well-defined and measured Q(LET).) ICRP, instead, now propose the use of complex anthropomorphic phantoms and a priori defined radiation weighting and tissue factors (wR and wT) in the definition of those quantities. It is not clear at this time, however, whether these new quantities can be measured in practice (especially by simple, cost-effective dosimeter badges for personal and area monitoring). A possible future change of the weighting factors could lead to further changes in the definition of the operational quantities (conversion coefficients.) From the viewpoint of a manufacturer/supplier of dosimeters, exact, clear and stable definitions are an absolute necessity. Otherwise, a redesign and change of thousands or tens of thousands of dosimeters is neither feasible nor economical.
The change from dose equivalent (Sv) for skin and eyes to absorbed dose (Gy) will require new ICRP dose limits. Or by consequence, if the dose limits for skin and eye were not to change (1 Sv = 1 Gy), the dose limits for all radiation types for which wR>1 implicitly would increase by a corresponding factor. Although this might not be important for considerations of the dose to the local skin and possibly the dose to the lens from neutrons and protons, possible consequences on the dose limits need to be mentioned and discussed in the document.
The new definitions dramatically change the energy and angular responses of Hp and H* dosimeters to incident photons. A factor of >5 for low-energy photons cannot be introduced by changing the dose calculation algorithm or the calibration (at least for some / many dosimeter badge arrangement currently in use.) In that case, a change of all dosimeter badges, including new type testing and accreditation or approval procedures are necessary. We dare questioning whether the high costs incurred in this process are justified, especially if the current dosimeters provide a conservative estimate of the effective dose. A currently perfect dosimeter for Hp(10) will no longer fulfil the requirements of IEC62387 for photon energies below 40 keV. ICRP are encouraged to provide a comprehensive justification for the implementation of these changes, given that they might result in significant costs and efforts by manufacturers and dosimeter services, and appear to be proposed mostly to incorporate the very highest and the lowest radiation energies. Neither one of these inclusions may be of relevance for a large fraction of the individuals routinely monitored for radiation exposure, and who are either employed in the medical field (diagnostic imaging and nuclear medicine, only but a few in accelerator facilities) or in the nuclear industry or in the use and handling of radioactive sources.
Some of the tables and / or figures in the appendices appear to display inconsistent data. Data should be cross-checked and confirmed prior to publication of the document.
Specific
Line 306: the authors state that “[t]here is the possibility of significant sources of uncertainty in the assessment of the protection quantities from operational quantities.” It is not clear whether the authors mean the sources of uncertainty may be significant, or the magnitudes of these uncertainties. We recommend ICRP will clarify.
Line 399: “[t]he distribution of the fluence with respect to energy is given by: […]”
Line 403: “[t]he complete representation of the double differential of the fluence is written […].”
Lines 421-422: the authors provide a final statement relating to the particle radiance, and in the course introduce another quantity (energy radiance) which has not been defined. We contend that this sentence claiming that particle radiance “can be considered as basic in radiometry” (as opposed to the other quantities which are not “basic”?) does not add to the definition, and could be omitted.
Line 471: this sentence provides a reference to Section 3.3.3 which does not exist.
Line 480: for readers familiar with the current set of protection quantities, it might appear strange that a definition of equivalent dose is not included. ICRP might consider providing a more direct explanation for this decision.
Line 492: ICRP have decided to define operational quantities in such a manner that “the conversion coefficient […] relate[s] particle fluence to the maximum value of the effective dose.” While this appears to be a sensible choice for the purpose of radiological protection, it might be prudent for ICRP to include a justification for this decision.
Line 518: please elaborate on and explain what is meant by “the whole-body of the stylized eye model.”
Lines 536 and 571: please provide a reason why the symbols for directional absorbed dose rate in the lens of the eye and directional absorbed dose rate in local skin are in bold type.
Footnotes 1-3: the footnotes, which describe a crucial part of the geometry, the choice of coordinate system, are very difficult to interpret. A thorough revision may allow for easier comprehension by the reader. More specifically, in Footnotes 1 and 2: if \theta is the angle with respect to the z-axis, would its range not be from 0 to \pi, or 0 to 180 degrees, starting by being collinear with the positive z direction? What do the authors mean by “positive \theta pointing to the head;” what is negative \theta then? Footnote 3 is even more confusing, both technically as well as grammatically (run-on sentence.)
Line 582: “[f]or a given \Omega, the maximum value of effective dose is taken for radiation incident from left or right.” Is \Omega not the direction of incidence (Line 580) and defined uniquely? How is radiation then incident from left or right? Maybe schematic drawings of the coordinate systems used might support the text.
Line 640: please define “radiation field phantoms.”
Lines 714-723: the use of “=”-signs in the parentheses is rather confusing; they could be omitted.
Line 723: while H’(3) is divided by \Phi, Hp(3) is not. The latter expression appears to be incorrect.
Lines 1191-1208: this section certainly appears to be correct, but seems to have very little connection to the rest of the document, in particular the second paragraph (Lines 1201-1208.) ICRP are encouraged to elaborate on the significance of this section with respect to the proposed new operational quantities.
Line 1297: please explain “[…] the response above neutrons of energy of 50 MeV […]”
Appendix A, Figure ?: is the coordinate system in the right portion of this figure right-handed? If not, why? Is this schematic consistent with Footnotes 1 and 2 earlier?
Line 1882: “[t]he energy loss of charged particles […] is calculated […]”
Line 1885: “[t]ransport of photons and electrons is simulated […]”
Line 1899: please explain “3-5 GeV c-1.”
Line 1913: “[e]nergy deposition for nuclei other than hydrogen is calculated […]”
Line 1924: “[n}eutrons, protons, electrons and photons are transported […]”
Line 1929: “[…] MCNP6, version 1.0, use pointwise […]”
Line 1933: please explain “[t]he code mix and matches tabulated […]”
Line 1940: “[…] a number of nuclides.”
Line 1956: “[…] contribution to organ dose was shown to be much less than 1%.” Shown by whom? If outside the scope of this document, a reference would be needed.