Patient dosimetry and a novel approach to establishing Diagnostic Reference Levels in dental radiology

Diagnostic Reference Levels provide a method of ensuring that patient doses in medical procedures are kept at acceptable levels. Their application in dentistry can provide an indication of current dose levels and can assist in potentially significant dose reduction in Ireland given the number of patients screened annually. This study involved retrospective analyses of entrance surface dose and dose-width-product measurements obtained in Irish Dental Practices for both Intra-Oral and Panoramic units respectively, followed by comparisons with Monte-Carlo generated computer models of these procedures. Analysis was performed on data from 33 Intra-Oral units for an Adult Mandibular Molar entrance surface dose, 198 readings for a proposed mGy/mAs reference level and 50 Panoramic machines for a dose-width product investigation. The third quartile value of the entrance surface dose for a standard Adult Mandibular Molar Intra-Oral radiograph is (2.40 ± 0.92)mGy, compared to a computer-modelled value of 2.60 mGy. The third quartile mGy/mAs value for Intra-Oral procedures is (1.03 ± 0.38)mGy/mAs, compared to a computer-modelled value of 0.75 mGy/mAs. The third quartile dose width product for an Adult Panoramic radiograph is (59.89 ± 20.97)mGymm, compared to a computer-modeled value of 62.40 mGymm. It is proposed to introduce Diagnostic Reference Levels of 2.4 mGy for an Adult Mandibular Molar Intra-Oral radiograph and 60 mGymm for an Adult Panoramic radiograph. The use of a new reference quantity in Intra-Oral radiology is also suggested. This has a value of 1 mGy/mAs and may be introduced alongside established procedures. These levels can be taken as guides to acceptable doses, but it should be noted that further reductions are practical under ALARA principles.