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.
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.