Operational Quantities for External Radiation Exposure

Draft document: Operational Quantities for External Radiation Exposure
Submitted by Miha Furlan, Dosilab AG
Commenting on behalf of the organisation

•    The joint effort of the ICRU and ICRP to improve the concept of operational quantities in radiation exposure by clarification and unification is absolutely appreciated. Weaknesses of the present approach are addressed and pragmatically solved. This is a clear progress in terms of basic principle and conception.

•    The report may be considered as a stimulus for discussion because it evokes significant consequences. One, for which the report lacks a specification, is the metrological feasibility. It is desirable that the proposed operational quantities are also measurable quantities. We have severe doubts, however, that there exists any dosimetric system (at reasonable cost) that can satisfy the response over the entire energy and/or particle range as treated in the report. Development and implementation of new dosimetric systems induced by a possible change in the operational quantities would not only generate huge costs. It is likely to provoke an insecurity in the monitored workers which are suddenly told that their personal doses are now different by a significant factor of up to 5. Changing a widely accepted and trusted concept can cause more harm compared to what we gain from a theoretically more adequate system. The risks of such a transition should not be underestimated.

•    Measurements are by default accompanied by measurement uncertainties. Should the recommendations be adopted and technically realized by monitoring services, the conversion coefficients only make sense if their uncertainties are given as well. This is not just the numerical uncertainty of a simulation but should include modelling parameter uncertainties and potential future corrections, like tissue weighting factors. Otherwise, the new operational quantities might be misunderstood as being exact and fundamental.

•    Even though the proposed new Hp more appropriately reflects the quantity relevant to radiation protection, the conversion factors are lower compared to Hp(10) by a factor 2 to 5 in the x-ray energy range which predominates in the medical sector. Hospitals which are always under pressure to tighten their budget are tempted to cut down on radiation protection effort accordingly. This is certainly not the goal as it undermines optimization and safety.

•    In the light of the above, we are confident that the report on new operational quantities inspires the community to proceed with discussing and improving on radiation protection concepts. We strongly recommend to complement the report by systematically addressing metrological feasibility and implications for practical applications.