Operational Quantities for External Radiation Exposure

Draft document: Operational Quantities for External Radiation Exposure

Submitted by Linda Persson, Swedish Radiation Safety Authority
Commenting on behalf of the organisation

The Swedish Radiation Safety Authority, SSM, has reviewed the ICRU and ICRP joint report Operational quantities for external radiation exposure. The comments are grouped into general comments and editorial comments.

General comments

SSM supports the combined effort of ICRP and ICRU to formulate operational quantities that give more accurate estimates of the protection quantities. The proposal is a step toward a simplified system of radiation protection quantities where the fewer new operational quantities also simplifies the usage of the units sievert and gray. This should facilitate a better understanding of, and communication about, radiation protection. However, since the publication only considers external exposures, it should be clarified whether the unit equivalent dose would still be used for organ doses from internal exposure. For example, in emergency exposure situations the thyroid organ dose, especially for children, is an important protection quantity. Many of the comments given below are actually reflecting a general proposal to consider if whether the system of radiation protection quantities could be stretched even further towards a more simplified system of quantities.

The conversion factors for Ambient dose and Personal dose are calculated using the ICRP/ICRU adult reference phantom. It is however not clear if the conversion factors are only valid for adults. A clarification of whether the conversion factors are valid for all individuals, also children, is needed.

The report states that its content is valid below 100 mSv, while ICRP 103 uses the formulation around 100 mSv. The wording should be harmonised, or a clarification included about the slightly different choice of valid dose interval.

Both the ambient dose and the personal dose are defined in terms of maximum effective dose, although with different incident directions and irradiation geometries included. Both quantities aim to give an estimate of the maximum effective dose, but using different instrument types. It is not obvious if there is really a need to separate between the two quantities, neither why the personal dose is defined at a point on the body. An alternative would be to define the personal dose at a point in space (as ambient dose) and consider the body as "a part of the measuring device" that changes the radiation environment due to e.g. scattering. The calibration of such a device would be performed on a phantom to include the scattering effects. Or possibly even better, it could be considered to replace ambient dose and personal dose with a single quantity relating kerma or fluence to maximum effective dose.

The difference between the directional absorbed dose in the lens of the eye, and the personal absorbed dose in the lens of the eye, seems only to be whether all directions are included or not. This is not clearly stated and a clarification of how the two quantities are related could be considered. Further, it could also be considered whether the directional absorbed dose to the lens of the eye is really needed as a quantity of its own, but rather as a step (one incident direction) in the definition of personal absorbed dose to the lens of the eye (all incident directions).

The definitions of absorbed dose to the eye lens and to local skin, are given with reference to ICRU tissue and the eye lens model rather than the ICRP/ICRU reference phantom (ICRP 110). The reason is likely that the ICRP/ICRU reference phantom is a voxel phantom for which calculations of small/thin tissues and volumes cannot be done. However, a new polygon-mesh phantom is presently under development, which opens up the possibility to calculate all conversion factors by using the same phantom. Such an approach would simplify the conceptual framework for the conversion coefficients considerably.

A comment on what reports are superseded and some recommendations on how to handle the transition period would be needed before a recommendation of a new set of quantities is published. For example, how to handle that “skin dose” is reported as equivalent dose in Sv one month and then as absorbed dose to local skin in Gy the next month. This example and other complications need to be discussed further.

Before the report is published a review of the language and syntax in the report would be needed. For example, in the beginning of the report the formulation ‘absorbed dose TO the lens of the eye’ (‘absorbed dose TO local skin’) is used, but later in the report ‘absorbed dose IN the lens of the eye’ (‘absorbed dose IN local skin’) is used.

Editorial comments:

Line	Comment	Suggestion
185	The rule of ICRP is presented but not ICRU	Do the same thing for ICRU
185	The acronym ICRU is not explained.	Write out full name, acronym in brackets for ICRU.
185	Reference is missing for the ICRU report concerning quantities.	Give ICRU report 51 as reference.
209	The acronym ICRU is not explained.	Write out full name, acronym in brackets for ICRU.
218	“of” is missing after study	“.. study of the values …”
239-240	Double use of “is given”	Delete one “is given”
296	Explanation for figure 1 is missing.	Include an explanation in line with e.g. ''The quantities and their relationships described in this document are shown schematically in Figure 1, and are explained in subsequent sections.”
304	A reference for the 100 mSv level is missing.	Insert a reference to ICRP 103
323-324	"incident angles of incidence"	Delete "incident".
379	Reference to ISO 2008 is missing in the list of references (starting on line 2150)	Complete the reference list (starting on line 2150)
471	There is a reference to section 3.3.3 – but there is no section 3.3.3	Delete or correct the reference to 3.3.3.
474	Insert a new section for Absorbed dose to local skin
478	Last sentence is not relevant for this section	Remove the sentence or move it to introduction
379	Unclear sentence, remove “Such data”	Replace “Such data” with "these conversion coefficients"
480	Definition of Absorbed dose to the lens of the eye is missing	Insert a new section for Absorbed dose to the lens of the eye
493	It is not clearly stated how Emax is defined.	Clarify that Emax is given by the maximum value of E in the different irradiation geometries (if this is what is meant).
512	It is not clear if there really is a need to define the directional absorbed dose for the eye lens. The quantity is to our knowledge not in common use in practice.	Consider revising the proposal by excluding directional dose quantities.
529	It is not clear how the incident direction is defined.	Include an explanation (e.g. in spherical coordinates with radius…etc in relation to the reference coordinate system).
529	It is not clear how the incident direction is to be defined in a radiation field with several directions.	Include a clarification.
530	“area monitoring quantity”?	Take away area
531,533	The sentence beginning with "In the particular case of a unidirectional field…" is not clear. It is e.g. not clear what is meant by “…this direction…” or how "Ω₀" is defined and representing.	Rewrite the sentence in a suitable way.
532	It is not clear how a situation with a “unidirectional field” is related or differs from “specified direction of incidence, Ω” described in line 529.	Please, clarify.
535	See comment on line 512	See comment on line 512
542	It is not clear if there really is a need to define the directional absorbed dose in local skin. The quantity is to our knowledge not in common use in practice.	Consider revising the proposal by excluding directional dose quantities.
563	It is not clear how the incident direction is to be defined in a radiation field with several directions.	Include a clarification.
570	See comment on line 535	See comment on line 535
581	The definition of the conversion coefficient should include E_max.	Correct the equation.
583	It is not clear why the maximum value of E is chosen only between radiation incidence from left or right.	Include a clarification.
592	The formulation “…at a point on the head or body…” is a bit imprecise and confusing.	Could ”…at a point on the head or body…” perhaps be replaced with ”point of measurement”?
595	The footnote (2) clarification of the direction of incidence would be valuable also for the directional absorbed dose in the lens of the eye.	Consider to include a similar clarification at line 519.
596	The conversion coefficient d_plens,i(Ep,Ω) seems to be identical to d’_lens,i(Ep,Ω). It is not clear if there really is a need for different notations.	Consider using the same notation for the conversion coefficients to directional and personal absorbed dose to the eye lens.
611	The footnote (3) clarification of the direction of incidence would be valuable also for the directional absorbed dose in local skin.	Consider to include a similar clarification at line 544.
620	It is not clear how to interpret the formulation "…projected onto the upper and lower cylindrical surfaces perpendicular to and at the centre of the pillar;"	Consider a reformulation.
624	See 620	See 620
640	unclear sentence	Delete “phantoms exposed”
689	Coefficients to absorbed dose in the complete lens or in the sensitive cells, are not discussed in detail in the report. These might therefore be considered as ‘alternative conversion coefficients’	Consider including “alternative” before conversion ..
695	The recommendations for interpolation should be included in ANNEX in appropriate locations	Include in annex
1014	A likely misprint using “ H´(0.07)” and “Hp(0.07)”.	Change to “H''(3) and Hp(3)”
1083	Unclear what is meant “complete” in “ … maximum for complete lens …”	Correct or clarify
1086-1087	The last sentence “There is concern in nuclear…” seems a little bit misplaced here.	Remove or move to introduction.
1093	Misprint in "...d''_{local skin slab}(a) and d''_{local skin slab} (a)…" that should read "...d''_{local skin slab} (a) and d_{p local skin slab} (a)…"	Correct accordingly
1185-1186	It is written “In high-energy and complex radiation fields, there are no traceable reference fields to characterize and calibrate instruments.” There is however no indication or guidance how to handle this situation.	Add a comment, guidance or reference on how to act in situations with high-energy and complex radiation fields.
1194	Rephrase to be more general as this is not only valid for radiation monitoring at the fence of facilities.	Rephrase as:” Applications are radiation monitoring in nuclear, medical and other occupations with ambient dosimeters and in contaminated environments by radionuclides released from such facilities.”
1223	Unclear sentence	Insert “applied” i.e. “… in local skin applied”
1269-1270	The sentence starting with “In this were to take place, case, which…” is unclear.	A reformulation is needed.
1272-1298	The text in this section concerns otons and neutrons, and to some extent electrons, but other radiation qualities and energies are not included.	Perhaps some sentences should be included concerning other radiation qualities and energies.
1290	The text does not include the fact that some instruments would need to be modified not only to measure a different quantity, but also to display a different unit (Gy instead of Sv).	A comment could be included that instruments for measuring absorbed dose to the lens of the eye and absorbed dose to local skin need to be modified to display Gy instead of Sv.

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