The way we measure occupational radiation dose is due its first major change since 1985, and the medical sector has more at stake than any other. ICRU Report 95 proposes new operational quantities for external exposure.
I see this from the medical side, as an RPA, RWA and MPE who has spent over 20 years in the NHS and now advises clinics independently. Here is my view of what it means in practice.
What is changing
The dose limits are not changing. What changes is how dosemeters and survey meters calculate the number they report.
Effective dose, the quantity our limits are set in, cannot be measured. We estimate it with operational quantities such as Hp(10), defined in a simple plastic phantom. At the energies typical of diagnostic X-ray scatter, around 20–50 keV, Hp(10) overestimates effective dose by roughly two to four times.
ICRU 95 (with ICRP 147) proposes:
- Whole body: Hp(10) in Sv becomes Hp in Sv, based directly on effective dose in a computational human phantom.
- Area monitoring: H*(10) in Sv becomes H* in Sv.
- Eye lens: Hp(3) in Sv becomes absorbed dose to the lens, in Gy.
- Skin and extremities: Hp(0.07) in Sv becomes absorbed dose to local skin, in Gy.
In short: same exposure, more realistic and usually lower readings at diagnostic energies. Adoption is expected to be phased over 10–15 years, and nothing changes in the UK until a national position is agreed and IRR17 and the guidance are updated.
My view: how it affects medical practice
On balance, I think the change is right for the medical sector. UNSCEAR estimates that around 80% of radiation workers worldwide are exposed mainly to low-energy photons, and most of them work in healthcare. For those staff, the current system has been over-reading for decades. But the benefit is uneven, and some areas will feel the change more than others.
- Interventional radiology and cardiology: whole-body readings should fall noticeably, but eye lens doses will not fall to the same extent. I expect the eye lens, not whole-body dose, to become the main driver for classification and monitoring in these teams. That could mean more eye dosemeters, not fewer.
- General radiography, CT and fluoroscopy: recorded doses for most staff are already low and will fall further. Few practical changes beyond new dosemeters and recalibrated survey meters.
- Nuclear medicine and PET: at 140–511 keV the old and new quantities are closer, so the effect is smaller. Extremity doses from preparing and injecting radiopharmaceuticals will remain the main concern.
- Dental and small private clinics: most staff are unclassified with near-zero doses. The main impact will be any change in dosemeter supply and cost, not in risk.
- Shielding: claims of halving shielding should be treated with caution. UK diagnostic shielding design is largely based on air kerma and dose constraints, so savings depend on updated guidance. Existing rooms will not need altering.
Practical considerations
- Lower readings are not lower risk. If staff see their doses halve overnight, some may relax on aprons, ceiling shields and eyewear. Communication needs to be clear that the exposure has not changed, only the estimate.
- Eye lens protection could be neglected just as it becomes the limiting dose.
- Dose record continuity. Old and new readings will not be directly comparable. Investigation levels, trends and lifetime records will need a clear switchover point.
- Cost falls unevenly. New or recalibrated dosemeters and instruments cost the same per unit for a single-room clinic as for a large trust, but weigh far more heavily on the small user.
- Voice in the consultation. Large organisations will be heard. Small private clinics, dental practices and the independent advisers who support them also need to be.
What medical employers should do now
There is no legal requirement to change anything yet. IRR17 and the current quantities remain in force. Proportionate steps for now:
- Be aware: make sure your RPA and Radiation Protection Supervisors know the change is coming.
- Review eye lens monitoring in IR and cardiology now. It is good practice regardless, and it will matter more under the new system.
- Ask your dosimetry service about their plans and timescales.
- Respond to the UK consultation when the DESNZ survey is circulated, so the medical sector's view is represented, including from smaller providers.
Final thoughts
ICRU 95 brings the science closer to what actually happens in the body, and for most medical staff that is a welcome correction. The real test will be implementation: protecting the eye lens, keeping records consistent, and making sure lower numbers do not lead to weaker practice.
If you would like to discuss what this may mean for your service, please get in touch via www.radorris.com.
Shelan, Radorris — RPA, RWA and MPE
📚 References
International Commission on Radiation Units and Measurements. ICRU Report 95: Operational Quantities for External Radiation Exposure. 2020.
International Commission on Radiological Protection. ICRP Publication 147: Use of Dose Quantities in Radiological Protection. 2021.