Measurement of dose reduction factors for X-rays and its relevance in eye lens monitoring applications

Lead (Pb) goggles used by radiation workers while performing fluoroscopy-guided diagnostic and interventional procedures reduce the doses to eye lenses substantially. In majority of the cases, the dosimeter intended to measure eye lens doses is worn close to the eyes but outside the lead (Pb) goggles. In such situations, additional reduction factors are required to approximate the actual doses which eye lens might have received. However, the value of the dose reduction factor (DRF) for a given energy may vary due to the dependence on the methodology of measurement, that is, whether the dose is estimated free-in-air or on a phantom. Due to this reason, the DRFs quoted by suppliers or manufactures cannot be implemented directly for dose estimation. Free-in-air as well as on phantom studies for the measurement of DRFs for lead (Pb) goggles having equivalent thickness of 0.75 mm were performed using optically stimulated luminescence (OSL)-based dosimeters. Measurements were carried out for photon energies having relevance in interventional cardiology (IC) and radiology (IR), and other facilities where eye lens monitoring might be important. It has been found that the DRFs differ substantially for irradiations done free-in-air and on the phantom. The results showed that for X-ray energies relevant to IC/IR procedures, the DRF values were found in the range of ~60–90 and 7–15 for free-in-air and on phantom measurements, respectively. Similarly, the DRF values for N-80 as well as 241Am photons were found to be ~15 and ~3.50 for free-in-air and on phantom measurements, respectively. The difference in the DRF values for free-in-air and on phantom measurements would arise due to the presence of backscattering associated with the phantom studies.