Impact of the ICRU/ICRP proposal on operational quantities during interventional procedures: Investigation through spectral measurements

In low-energy photon fields, such as those encountered during fluoroscopy-guided interventions, the current operational quantity for area dosimetry, ambient dose equivalent H*(10), overestimates effective dose by roughly a factor of two. ICRU Report 95 introduces a revised set of operational quantities intended to better align with protection quantities, replacing H*(10) with ambient dose H* for area monitoring. Experimental data validating these changes in realistic clinical environments remain scarce. This study examines the differences between current and newly proposed operational quantities in scattered radiation fields representative of occupational staff exposure during fluoroscopy-guided procedures. Measurements were performed using a Timepix4 hybrid pixel detector operated simultaneously as an X-ray spectrometer and dosimeter. The detector provides energy-resolved photon fluence measurements convertible into operational dose quantities via published fluence-to-dose conversion coefficients. Measurement campaigns were conducted in a urology theatre and an interventional cardiology (IC) theatre under realistic clinical conditions. Photon spectra were recorded at staff positions representative of standard procedures and converted into current and newly proposed quantities relevant to whole-body, skin, and eye lens exposure. The influence of beam angulation and additional shielding was further investigated in the IC theatre.For whole-body exposure, ratios between H* and H*(10) ranged from 0.52 in urology to 0.59 in IC. Quantities relevant to skin and eye lens exposure remained close to unity, with deviations not exceeding 5% and 8%, respectively. Beam angulation and shielding induced only minor variations in these ratios, below 5%.These results provide the first experimental validation of ICRU Report 95 quantities in interventional workplaces. Whole-body dosimetry is most affected by the transition, while skin and eye lens monitoring should remain largely unchanged. Ambient dosimeters calibrated in H*(10) used in low-energy photon fields may be recalibrated using a single procedure-specific calibration factor, whereas calibration procedures for skin and eye lens dosimeters may remain unchanged.