From an academic point of view the new concept is good, solving a few problems that exist in the current concept of H*(10) and Hp(10). On the other hand, there are severe doubts that the concept can be put into practice for the use in radiation protection. We see the following weaknesses:
1) The new concept cannot be implemented in practice. No dosemeters, currently available, will be able to measure Personal or Ambient Dose while fulfilling the requirements of standards like IEC62387. The change would require development and subsequent production of a completely new set of personal dosemeters.
2) The implementation worldwide will cost an estimated more than 150 Mio Euro, for individual monitoring only. It will ruin many of the smaller individual monitoring services. As such, there is no balance between costs and benefits.
3) In practice, the new concept will downgrade radiation protection and will contradict the ALARA principle
To 1) Practical consequences to individual monitoring of occupational exposed workers
In the draft, the consequences of the new quantities to the design and calibration of actual or future personal dosemeters are only considered for photon energies >70 keV (chapter 7, line 1272-1281). This is the energy range where the changes are quite small. For the field of individual monitoring the effects for X-ray qualities from 10 keV to 70 keV are of biggest importance. In Germany more than 50% of all monitored occupationally radiation exposed individuals work in X-ray fields. Additionally, nearly all personal photon dosemeters in worldwide individual monitoring measure radiation qualities at least between 20 keV and 6 MeV. For this important field of application the draft says only “Modifications of existing instrumentation might be required where this is considered to be necessary….” (line 1286-1289), not going into details about the consequences of the new concept.
Especially in X-ray fields, the effects of the new quantities on dosemeters are dramatic - see figure 4.1, 4.2 and 4.3 of the draft. An energy and angular dependent over estimation of a factor of 2 to 5 has to be corrected by design and dose calculation algorithm for all personal and ambient dosemeters. This is an extremely complicated task in practice. As a technical solution 10 mm – 60 mm thick PTFE filters, depending on energy, have to be added on top of the current dosemeters, which is not practical at all. Consequently, all (!) dosemeters used in x-ray fields will have to be redesigned and manufactured new in order to fulfill performance requirements defined in standards like IEC 62387 for photon energies between 20 keV and 6 MeV and incident angles within +/-60°.
When constructing new dosemeters, one have to take into account the effects of energy dependency, detector sensitivity, filters (especially metal filters) and angular response combined with production tolerances and requirements by standards like IEC62387. For us, an individual monitoring service working in the field of research and development of new dosemeters for radiation protection, it is obvious, that the construction and fabrication of a cheap and user friendly, one or two element detector systems for the measurement of the new Personal or Ambient Dose in individual monitoring is nearly impossible.
We claim that:
Even if there is a practical solution, it is worth to take a look at the results of international intercomparisons in individual monitoring in recent years, like the EURADOS intercomparisons in Europe. This data gives an indication on the expected quality of newly adopted or constructed systems and the period for implementation and optimization in individual monitoring. When the EURADOS intercomparisons started in 2008, about 7% of all measured Hp(10) values where outside the requirements (Figel, 2016), while some system types showed 25% of outliers. Quite a few routinely used dosimetry systems were not able to measure Hp(10) at all, 23 years after the introduction of Hp(10) in 1985 (ICRU 39, 1985). Eight years later, in 2016, the general results looked better, but still systems could be identified that were not able to measure Hp(10) by construction (EURADOS, 2017) - more than 30 years after ICRU 39. The technical task introducing Hp(10) in 1985, adding only 10 mm of tissue equivalent on top of existing dosemeters, was much easier than the changes that are necessary for implementing the new quantities proposed now.
To 2) Economic impact
For an individual monitoring service like “Auswertungsstelle” at Helmholtz Zentrum München, Germany, monitoring approximately 165,000 exposed workers, the new concept means an investment of more than eight million Euro to buy new dosemeters, in addition to development costs. We estimate that the costs to implement the new concept worldwide, including development, will surpass 150 million Euros by far. Smaller monitoring services might not be able to finance the process, especially if they are in public hands.
This amount of cost is in no relation to the minor benefit in occupational exposure of the small number of radiation-exposed workers in high-energy fields, where a simple field correction factor can be used.
To 3) Contradicting ALARA principle
As the current quantities H*(10) and Hp(10) are conservative for X-ray qualities (factor 2-5), shielding thicknesses, tube shielding etc., are also conservative relative to dose measurements using the new Ambient and Personal Dose. If the new quantities are used to estimate shielding thicknesses, the shielding can, and will, be reduced by industry to reduce costs. As a result, the collective dose for radiation exposed workers in X-ray diagnostics will increase compared to the current status. This is against the principle of ALARA and ICRU has to address this issue.
Summary:
From a practical point of view, there is no need to make any changes to the current concept of radiation protection quantities. The current concept is for the majority of occupationally exposed individuals, conservative and follows the ALARA principle. For radiation qualities and the very few work places where the current concept is not conservative, field correction factors are easily applicable. From an academic point of view, the new concept is better but the benefits in practical radiation protection are in absolutely no relation to the estimated cost of more than 150 million Euros and the increased collective dose to workers in X-ray diagnostic fields.
References:
(Figel, 2016): Figel, M., Stadtmann, H., Grimbergen, T. W. M., McWhan, A., Romero, A. M., 2016. EURADOS Intercomparisons on whole-body dosemeters for photons from 2008 to 2014. Radiat. Prot. Dosim. 170, 113-116.
(EURADOS, 2017): http://eurados.org/en/Actions/Intercomparisons : preliminary results presented at the participants meeting which took place at the AM2017 on 28. Feb. 2017 in Karlsruhe.