Radiation shielding transmission data for modern digital radiography.

BACKGROUND

Radiography is one of the most widely used x-ray imaging modalities. In National Council on Radiation Protection and Measurements (NCRP) Report No. 147, transmission data for radiographic systems were evaluated on those installed before 2000. For x-ray systems (except intraoral dental) manufactured on or after June 10, 2006, the U.S. required minimum half-value layer (HVL) was increased; for example, 2.9 (2.3) mm Al at 80 kV, where the value in parenthesis denotes the earlier requirement before the above date.

PURPOSE

To calculate the transmission of the broad x-ray beam of modern digital radiography (DR) through shielding materials.

METHODS

X-ray beam HVLs on two DR systems (Agfa DR 600, GE Revolution XR/d) were measured in 10 kV increments between 60 and 120 kV, with a calibrated ionization chamber (Radcal model 10 × 5-60) and varying thickness of aluminum 1100 plates. Monte Carlo (Geant4) simulation was performed to calculate the transmission of broad x-ray beams through lead, concrete, gypsum, and steel, with x-ray HVLs matching those of the DR 600 at two beam filtrations (default, 1 mm Al plus 0.1 mm Cu added filtration). The transmission data were fitted to the Archer equation.

RESULTS

HVLs on two DR systems with default beam filtration were consistent (median difference, 2.1%; maximum difference, 5.5%). An additional beam filtration option (1 mm Al plus 0.1 mm Cu) on the DR 600 substantially increased HVLs by 45.2%-61.2%. Transmission fitting parameters were provided for seven tube voltages (60-120 kV) at two beam filtrations.

CONCLUSION

This work presents transmission data for modern DR systems, indicating increased x-ray beam filtration compared to the primary x-ray beam in NCRP Report No. 147. The updated transmission data can enhance structural shielding evaluations at individual tube voltages or with a workload distribution.