The current value for weighted average primary plus scatter kerma at 1m for intra-oral radiography shielding assessment is based on scatter radiation measurements made with the trunk of a RANDO phantom and an assessment of primary transmission that is unverified. Measurements of primary transmission and scatter radiation during intra-oral radiography were made at 30° intervals through a full 360° rotation using two anthropomorphic head phantoms and similar equipment at three different sites. The results suggest that a scatter factor of 5Gy(Gycm ) and a primary transmission of 0.03% of the entrance surface dose are more appropriate and, therefore, we recommend that the weighted average primary plus scatter kerma used for shielding calculations can be reduced from 1 to 0.5Gy per exposure at 1m. This factor will adequately account for exposures made at 60 and 70kV using a range of intra-oral units.
Worrall, M., McVey, S., & Sutton, D. G. (2012). Proposals for revised factors in intra-oral radiography shielding calculations. Journal of Radiological Protection, 32(3), 243-249. https://doi.org/10.1088/0952-4746/32/3/243